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Microphone Terminology

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This long post is from this link at www. sweetwater.com, which may disappear, and I thought it would be good to have it all here.

http://64.233.161.104/search?q=cache:650GV...lient=firefox-a

· 2:1 Rule of Ambience

· 3:1 Rule of Microphone Placement

· A-B Stereo

· Absolute Phase

· AES42-2001

· Ambience

· Ambisonics

· Anechoic

· Back-Emf

· Backline

· Backplate

· Baffled Stereo

· Bass Management

· Binaural

· Bleed

· Blumlein Microphone (or Blumlein Pair)

· Body Pack

· Boom Operator

· Boundary Microphone

· Brownian Movement/Motion

· Capsule

· Cardioid

· Claw/Drum Claw

· Coincident

· Coloration

· Compression Driver

· Condenser Microphone

· Conductor

· Contact Mic

· Control Room

· COSM

· De-Esser

· Decca Tree

· Decoupling

· Diaphragm

· Din Stereo

· DirectSound

· Diversity Receiver

· Ducker/Ducking

· Dynamic (Microphone)

· EIN

· Electret

· Equivalent Input Noise (EIN)

· Feedback

· Field Effect Transistor (FET)

· Figure 8

· Front Address

· Gain Before Feedback

· Gap

· GoBo

· Gooseneck

· Handling Noise

· Hi-Z

· Hypercardioid

· In Line Mixer

· Inverse Square Law

· Jecklin Disc

· Large Diaphragm

· Lavalier

· Line Input

· Lobar Polar Pattern

· Lobe

· M-S Stereo

· Maximum SPL (Sound Pressure Level)

· Medium Diaphragm

· Mic Amp

· Mic Level

· Microphone

· Minimum Terminating Impedance

· Mix-Minus

· Moving Coil

· Multi-Pattern

· Multipattern

· Near-Coincident Pair

· Neodymium

· NOS

· Off-Axis

· Omnidirectional

· On-Axis

· On-Axis

· Op Amp

· Open Mic

· ORTF

· Pad

· Phantom Power

· Phase Cancellation

· Piezo

· Plate Reverb

· Plosive

· Point-to-Point Wiring

· Polar Pattern

· Polarize

· Pop

· Pop Filter

· Potential Acoustic Gain

· Potting

· Preamp

· Prepolarization

· Pressure Microphone

· Pressure-gradient Microphone

· Proximity Effect

· PZM

· Reverb

· Ribbon Mic

· Ring Out

· Sensitivity

· Shockmount

· Shotgun Microphone

· Shuffler

· Side Address

· Signal Path

· Small Diaphragm

· Sound Card

· Spaced Omni

· Sputter/Sputtering

· Squelch

· STC

· Stereo Bar

· Supercardioid

· Suspension Basket

· Talkback

· Thermal Noise

· Time Alignment

· Transducer

· Transformer

· Trim

· True Diversity

· Unidirectional

· Variable Pattern Mic

· Wind Screen

· Wireless Receiver

· Wireless Transmitter

· Xophonic

· XY Stereo

· Zeppelin

· Zoom Microphone

2:1 Rule of Ambience

To capture an equal amount of room ambience, a cardioid microphone must be placed twice as far from a source as an omnidirectional pattern microphone. Keep this in mind the next time you are trying to capture some of a room's natural sound when recording!

3:1 Rule of Microphone Placement

Yesterday we discussed the 2:1 Rule of Ambience. Today let's go one better with the 3:1 Rule of Mic Placement. When using two microphones to record a source, normally you will get the best results by placing the second mic three times the distance from the first mic that the first mic is from the source. Confusing? An example: If the first mic is 1 foot from a source, the second mic should be placed 3 feet from the second mic. Using the 3:1 Rule will minimize phase problems created by the time delay between mics.This rule originated when engineers were micing multiple sources in the same vicinity. The same principle applies. If you are recording two different sources of sound, their respective microphones should be at least three times further apart than they are close to their respective sources. Keep in mind that rules are meant to be broken; you may prefer the sound created by ignoring the 3:1 Rule - experiment and let your ears be your guide!

A-B Stereo

Sometimes known as Time Difference Stereo, A-B Stereo is a stereo miking technique that employs two spaced omnidirectional microphones to capture a stereo image. The microphone spacing introduces small differences in the time or phase information contained in the audio signals (according to the relative directions of the sound sources). As the human ear can sense these time and phase differences in audio signals and use them for localization, they will act as stereo cues to enable the listener to "capture the space" in the recording, and experience a stereo image of the sound-field. Omnidirectional microphones and A-B Stereo are often the preferred choice when the distance between microphone and the sound source is large. One reason is that true omnidirectional microphones are able to capture the true low frequencies of a sound-source regardless of the distance, while directional microphones are influenced by the proximity effect. Directional microphones will therefore exhibit loss of low frequencies at larger distances. (See Spaced Omni)

Absolute Phase

A positive pressure to a microphone diaphragm will (in most mics) produce a positive voltage at its output. If the correct polarity (see WFTD archive polarity) of the signal is maintained throughout the signal path this should ultimately produce a positive voltage at the speaker terminal, which will (on most speakers) cause the speaker to move forward creating a positive pressure wave in the listening position. This is known as absolute phase (see also WFTD archive phase): The original polarity of the source sound is thus reproduced in phase by the loudspeaker for listening.

AES42-2001

An emerging new AES standard that's an extension of the current AES3 digital audio interface standard. AES42-2001 provides for interfacing digital microphones and includes the ability to transmit and receive a great deal of data along with the digital audio signals. For example, a user of a digital microphone will be able to remotely control parameters such as polar pattern, pre-attenuation, low cut filter, pre-amplification, mute, and polarity in addition to getting feedback about signal levels and the status of the mic.

Ambience

Generally thought of as the character or quality of some environment. In audio we specifically mean the acoustical (sonic) characteristics of a space, including everything from the size of the space to what type of sounds are a normal part of it. For example: a big auditorium may, as part of its sonic character, have a large HVAC (Heating, Ventilation, and Air Conditioning) system that runs, which provides a constant background noise level. Any noise existing or injected into a space will of course be acted upon by the space based on things like size, shape, and the various surfaces that reflect sound. Humans have a great ability to discern a lot about an environment from these aural cues. As an experiment put up a microphone in some different rooms of your house or apartment and make recordings. Listen to them later at an exaggerated volume so you can really hear the ambient noise level as it is being acted upon by the room acoustics. You will most likely be able to identify each room by its sound.

Ambisonics

A British-developed surround sound system designed to reproduce a true three-dimensional sound field. Based on the late Michael Gerzon's (1945-1996; Oxford University) famous theoretical foundations, Ambisonics delivers what the ill-fated quadraphonics of the '70s promised but couldn't accomplish. Requiring two or more transmission channels (encoded inputs) and four or more decoded output loudspeakers, it's not a simple system; nor is the problem of reproducing 3-dimensional sound. Yet with only an encoded stereo input pair and just four decoded reproducing channels, Ambisonics accurately reproduces a complete 360-degree horizontal sound field around the listener. With the addition of more input channels and more reproducing loudspeakers, it can develop a true spherical listening shell. As good as some think it is, a mass market for Ambisonics has never developed due to several factors. First, the actual recording requires a special tetrahedron array of four microphones: three to measure left-right, front-back and up-down sound pressure levels, while the fourth measures the overall pressure level. All these microphones must occupy the same point in space as much as possible. So far, only one manufacturer (first Calrec, bought by AMS, bought by Siemens, sold, now Soundfield Research) is known to make such an array. Next, a professional Ambisonics encoding unit is required to matrix these four mic signals together to form two or more channels before mastering or broadcast begins. And finally, the consumer must have an Ambisonics decoder, in addition to at least four channels of playback equipment.

Anechoic

Literally, without echoes. Anechoic refers to the absence of audio reflections. The closest thing to this situation in nature is the great outdoors, but even here there are reflections from the ground, various objects, etc. It is almost impossible to create a truly anechoic environment, as there is no such thing as a perfect sound absorber. At high frequencies, it is possible to create near-anechoic conditions, but the lower the frequency, the harder this is (Absorption is wavelength dependent. As an example, a 100 Hz wave is about 10 feet long; the absorber must be at least 1/2 a wavelength deep to function properly. It quickly becomes impractical to create a large enough space with enough material in it to absorb low frequencies).It is not desirable to create anechoic or near-anechoic conditions in a recording studio. The total absence of reflections skews perception, and will not result in good recording or mixing decisions. Anechoic chambers are used for testing and spec'ing microphones and loudspeakers, as well as for a variety of other audio measurements.

Back-Emf

Literally,, back-voltage, is a phenomena found in all moving-coil electromagnetic systems, but for audio is most often used with respect to loudspeaker operation. This term describes the action where, after the signal stops, the speaker cone continues moving (due to inertia), causing the voice coil to move through the magnetic field (now acting as a microphone), creating a new voltage that tries to drive the cable back to the power amplifier's output. If the loudspeaker does too much of this, the cone flops around unpleasantly. It is not pleasant-sounding. To stop back-emf, the loudspeaker must "see" zero ohms looking backward (a dead short), or as close to it as possible from the output of the amplifier.

Backline

A general term that includes all necessary band gear including guitar, bass and keyboard amplifiers, drums, microphone stands and cables, sometimes also encompassing keyboard instruments and rarely guitars and basses. It excludes any part of the house or stage monitor sound systems, which serve to amplify the backline gear. Originally a bit of tour jargon, the term is now accepted in touring groups' contract riders and insurance forms. Note that the term refers to the equipment itself and NOT to a specific area of the stage. Backline gear can be offstage, under the stage or in other locations.

Backplate

The part of a condenser microphone that's behind the diaphragm. The diaphragm is stretched over the backplate leaving a very small gap between them. The backplate and the diaphragm together form a sort of variable capacitor, the value of which changes as the diaphragm vibrates sympathetically with sound waves hitting it. This vibration modulates the supplied voltage between the two plates and gives the microphone capsule its output.

Baffled Stereo

When one is confused about how to mix in stereo and just mixes to mono instead. Actually it is really a generic term for a lot of different stereo miking techniques using an acoustic baffle to enhance the channel separation of the stereo signals. When placed between the two microphones in a spaced stereo set-up like ORTF stereo, DIN stereo or NOS stereo, the shadow effect from the baffle will have a positive influence on the attenuation of off-axis sound sources and thereby enhancing the channel separation. Baffles should be made from an acoustic absorbent and non-reflective material to prevent any reflections on the surface of the baffle to cause coloring of the audio.

Bass Management

A circuit or process that takes all the frequencies below 80Hz (according to the Dolby spec) from the main channels in a surround or stereo mix and the LFE signal and mixes them together into the subwoofer. In other words, Bass Management is the act of placing an electronic bass frequency crossover on all the channels, and redirecting those bass frequencies. Stereo or surround rooms, especially with smaller near field monitors placed on the console, can benefit from the correct integration of Bass Management and a subwoofer. With such, the engineer is now able to hear low frequency anomalies caused by room rumble, microphone stand thumping, breath pops, and other undesirable artifacts. Plus, even the least expensive Dolby Digital consumer decoder, found in millions of homes, has bass management built in, allowing the bass from all channels to be fed to a single subwoofer - which means that control rooms with proper Bass Management will be able to make sure that their mixes translate well into consumer systems.

Binaural

A system of recording with a plastic replica of the human head, with microphones placed in the ears, replicating as near as possible human hearing functions regarding phase, directionality etc. This signal information is absent from ordinary microphone pickups. Signals from the two mikes placed in each ear of the dummy head are kept entirely separate all the way to the two drivers of the final listener's stereo headphones. The result is a convincing preservation of the 360° soundfield and localization abilities present where the dummy head was placed.

Bleed

In audio, bleed is the leakage of one audio source's output into another audio source's input. This can happen onstage, such as a drum or cymbal's sound bleeding into a guitar amp mic, or in the studio, such as the output from a singer's headphones leaking into the vocal mic. Some solutions to reduce bleed include: mic selection and placement - using a cardioid or supercardioid mic on a source to reject signals from other directions; use of noise gates to attenuate mic sensitivity so they don't pick up outside noise; and optimizing the gain stage of your mixer and peripherals to achieve an ideal signal-to-noise level.

Blumlein Microphone (or Blumlein Pair)

Named for Alan Blumlein (chief engineer at EMI in London during the 1930's, and a pioneer in stereo audio), a Blumlein pair uses two coincident bi-directional (or figure 8) pattern microphones set up at 90 degrees to each other. This stereo miking technique provides a strong center image, and good room ambience. When using this technique, absolute polarity in the entire audio system is essential, mic distance from the source is critical in balancing ambience with direct sound, and since so much ambience is captured, a good sounding room is critical. (See also WFTD "Coincident")

Body Pack

In the world of wireless performance a body pack is the device a performer wears somewhere on his or her body that houses the electronics that handle sending a signal to a remote receiver or, as in the case of personal monitoring systems, receives a signal from a remote location. Typically body packs hold a battery and some combination of electronics that do the transmitting or receiving, and amplifying. Some wireless systems do not require a body pack as all of these electronics can be housed right inside of a microphone or a small plug that can be connected directly to a guitar or other musical instrument.

Boom Operator

A member of the sound crew skilled in the operation of a long pole with a microphone on it, otherwise known as a boom microphone. Typically found in video and film work, the Boom Operator is responsible for capturing the audio of a given shot with his boom mic, while keeping it out of the shot. Boom operation is both physically grueling and artistically demanding.

Boundary Microphone

A type of microphone that detects sound pressure level (SPL) changes at a boundary of the acoustic space in order to reduce interference between direct and reflected sound. In a boundary microphone, the capsule is fitted flush in a surface that is large and flat compared to the wavelength of sound being captured. This produces a semi-omni-directional pick-up pattern. Boundary Microphone is also referred to as Pressure Zone Microphone (see WFTD PZM).

Brownian Movement/Motion

First demonstrated by Dr. Robert Brown (about 1827), the random, rapid, vibratory movement of tiny particles in a fluid such as water or air caused by collisions between them and molecules of the fluid. Brownian movement is known to be a significant contributor to the self-noise of microphones due to the action of moving particles against the diaphragm.

Capsule

The portion of a microphone that converts acoustic energy to electrical energy. The capsule usually includes shock mounts, acoustic isolators, protective covers and electronic circuitry in addition to the basic transducer. Also called an element. It's basically the 'heart' of any microphone.

Cardioid

A microphone polar (pickup) pattern. Characterized by strong sensitivity to audio from the front of the mic, good sensitivity on the sides (at 90 degrees, 6 dB less than the front), and good rejection of sound from the rear, the cardioid pattern can almost be visualized as a "heart-shaped" pattern (hence its name).The ability to reject sound from the rear makes cardioid patterns very useful in multi-miking situations, and where it is not desirable to capture a large amount of room ambience. Popular in both studio and live use (where rear rejection cuts down on feedback and ambient noise), cardioid mics are used for a very high percentage of microphone applications.Keep in mind that like all non-omnidirectional mics, cardioid mics will exhibit pronounced proximity effect (see WFTD archives, "Proximity Effect").

Claw/Drum Claw

Microphone holders that that clip directly onto drum kits or other percussion instruments such as congas or timbales. Drum Claws allow for easy positioning of mics to avoid having them hit by drummer's sticks and eliminate the need to carry a number of mic stands while keeping the stage clear.

Coincident

In audio terms, coincident is normally used in the context of stereo microphone pairs. The idea is to get the capsules of the two mics as close together as possible to minimize phase problems in the final recording. Often the mics are directional (i.e. cardioid) and are "stacked" one atop the other, commonly at an angle of 90 degrees. Another coincident miking approach is called "MS" or "Mid-Side". Here a bi-directional (figure 8) and cardioid mic are placed close together. By combining the outputs of the two mics in varying amounts, the apparent width of the stereo field can be changed.

Coloration

A subjective term used in the audio industry to describe subtle types of alteration or distortion of sound. When we say some piece of audio has a certain "coloration" to it we mean that it doesn't sound pure, or as it normally would. The sound has been affected in some way. When audio passes through a device we say it "colors" the sound. For example, microphones color the sound, each in their own way. We choose microphones based largely on the type and degree of coloration we prefer. The same is true for literally everything in the audio chain. The subjective differences in sound - the colors - from one device to another provide us with different palette to choose from when creating our audio masterpieces.

Compression Driver

Developed by Bell Laboratories in the early 1930's the compression driver is a special type of dynamic loudspeaker (meaning it works just like a dynamic microphone, but in the opposite direction) designed to fit onto the small end of a horn. The horn acts like an acoustic transformer, with the driver providing a high sound pressure level at throat of the horn, with the mouth of the horn providing a large area of low pressure to radiate the sound efficiently into the air. They work by attaching a voice coil to a diaphragm (much like any tweeter) whose surface radiates sound into the horn through a small opening known as the throat, which is where the compression occurs. There are many sophisticated design variables involved in producing a high quality compression driver.

Condenser Microphone

The condenser microphone is a very simple mechanical system, with almost no moving parts compared to other microphone designs. It is also one of the oldest microphone types, dating back to the early 1900's. It is simply a thin stretched conductive diaphragm held close to a metal disk called a backplate. This arrangement basically produces a capacitor, and is given its electric charge by an external voltage source. This source is often phantom power, but in many cases condenser mics have dedicated power supply units. When sound pressure acts on the diaphragm it vibrates slightly in response to the waveform. This causes the capacitance to vary in a like manner, which causes a variance in its output voltage. This voltage variation is the signal output of the microphone. There are many different types of condenser microphones, but they are all based on these basic principles.

Conductor

The opposite of a resistor. A conductor passes (or conducts) electricity easily. All conductors do have some resistance to current flow, but the idea is that this resistance is relatively low. In electronics a conductor is something specifically put in place for the purpose of conducting electricity down a specific path. This may be to protect other assets, as is the case with something like a lightening rod, or simply to get a signal from point to point in the most efficient manner. In wire terminology conductors are specifically for carrying the desired signal. This may be an audio signal in your studio or an electrical "signal" in your household wiring. A ground wire or shield generally is not counted as a conductor because its purpose is not solely to carry a signal, but rather is for safety and/or rejection of interference. So even though a standard microphone cable has three electrical paths it is really two-conductor cable, or sometimes referred to as "two conductors and a shield." In unbalanced cable this distinction gets blurred because the shield is also used as a conductor.

Contact Mic

A microphone designed to be in physical contact with the object producing sound. A contact mic receives and derives most of its audio signal from mechanical vibrations instead of airborne sound waves. These are sometimes called piezo or transducer mics, but contact mic is the most accepted name. They are also sometimes confused with PZM microphones because they too are generally affixed to some surface, however they still work from air vibrations and are thus shouldn't be considered contact mics.

Control Room

In general this refers to a space - usually an enclosed room, or booth - where the operations of something are handled, the central control point. In radio and television production, this refers to the room that houses the equipment used to bring all the audio and video signals together into a composite signal that's broadcast or recorded. All the different cameras and microphones are fed into video switchers and audio mixers here. Similarly in theater applications, this is generally where all the audio signals are mixed, additional recorded sound effects may be added, and where the lighting is controlled (though these may be in separate control rooms). In theater it is sometimes referred to as a "Bio-Box," which comes from the Greek word "Bios," or Way of Life. In a recording studio, the control room has a similar function. It's where the engineers and producers sit and take care of making sure good signals get recorded as well as controlling, in many cases, what the band hears during a performance. Ideally, control rooms are designed to be carefully regulated in terms of sound isolation and accurate sound reproduction, as this is where the final decisions are made about how a recording will sound. On some audio equipment - typically mixers - there are control room outputs and associated control room level (volume) and mix controls. This pertains to sending signals to the control room speakers, which are usually a specially selected set of very accurate speakers designed to enable producers and engineers to hear a true reference of the audio signals being recorded and mixed. In some cases these speakers are custom designed to properly react with the control room space. In other cases a control room space may be built with a specific set of speakers (and other equipment) in mind.

COSM

Abbreviation for Composite Object Sound Modeling. COSM is a powerful modeling technology that Roland premiered in 1995 with the VG-8 V Guitar System, and continues in the newer VG-88 system. It enables guitarists to emulate a range of classic and modern guitars, amps, cabinets, and microphones, plus it can produce "futuristic" synth-like tones. Today COSM can be found in keyboards, digital recorders, mixers, etc. It can model rotary effects, different speaker colorations, and can even approximate expensive microphones using just an ordinary dynamic mic. Its name comes from "composite object" because its core function revolves around breaking audio producing or reproducing devices down to their component parts and creating a set of instructions to emulate how these various parts interact with each other to produce a new composite that can be dynamically controlled. Of course, that's what all modeling is, but Roland coined this name to call attention to it.

De-Esser

A special type of compressor that is tuned to be sensitive to sibilant sounds, or sounds with high frequencies such as the sound produced by the letter "s", hence the name de-esser. The need for de-essing arises out of a combination of the presence peak many microphones have in their frequency response to accentuate vocal recording combined with close proximity vocal work and possible added high frequency boost from equalizers and tone controls. While these things often make a vocal track have more "air" and high-end clarity, they can also add enough accentuation to certain consonants (especially the "s") that they become too pronounced. The problem can range from being slightly annoying to being bad enough to cause distortion in the signal path. Many years ago broadcast engineers figured out they could tune compressors to be more sensitive to these frequencies, which in effect produces an automatic volume control that can turn down the audio anytime one of the sibilant sounds occur. In fact, any compressor with a sidechain input can be turned into a de-esser by inserting an EQ and boosting the offending frequencies. Even more flexibility comes from using a multi-band compressor. The de-essing action no longer has to lower the overall signal level. It can just lower the level in the specific range of frequencies specified. Some modern de-essers, however, have very sophisticated circuitry and controls that are optimized for achieving results beyond what would be easy with a simple compressor with an EQ in the sidechain.

Decca Tree

A stereo miking technique. A Decca Tree configuration is characterized by having three omnidirectional microphones in a "T" shaped setup. Two of the microphones are positioned about two meters apart. The third microphone is positioned between the first two, but about 1.5 meters forward (closer to the source) of them. This configuration is sometimes used for orchestral recordings and film scoring due to its natural sound with good separation. It is useful in film because the image doesn't usually cause problems with Dolby or other surround processes. In many cases the Neumann M50 (or now, the newer TLM50) is used as the center microphone because of its unique directional characteristics and smooth sound.

Decoupling

The process of isolating one stage of an amplifier from another. Decoupling prevents unwanted oscillations (see WFTD Oscillator) and other noises that may occur due to unwanted feedback through common power supply connections (see WFTD Coupling). It also provides further filtering of the power supply to reduce any lingering AC ripple, producing a cleaner DC supply for the low-level preamp stages. This decoupling is often accomplished by adding a resistor in series with the power supply to a gain stage and a large-value electrolytic capacitor from the supply to ground after the resistor, however, there are a number of other designs employed as well. In acoustics decoupling refers to mechanically isolating masses from one another, particularly masses that are vibrating, such as speaker cabinets. This prevents the undesired transmission sound through additional materials that can result in a compromise in sound quality to he listener or at the microphone.

Diaphragm

In the audio world, diaphragm refers to the component in a microphone that vibrates sympathetically with air disturbances such as sound waves. It is typically a circular shaped very thin piece of mylar or other delicate low mass material that will range from .2 to 2 inches in diameter. When the diaphragm in a microphone vibrates it generates an electrical signal often by either moving an attached coil of wire in and out of a magnetic gap (in the case of moving coil microphones) or by changing the distance between it and another electrically charged plate (as in condenser microphones). These electrical impulses are then present at the output of the mic and ready for amplification as an audio signal.

Din Stereo

A stereo recording technique where two cardioid microphones are spaced 20 cm and angled 90° creating the stereo image. This is remarkably close to an ORTF configuration. The DIN stereo produces a blend of intensity between stereo signals and time delay stereo signals, due to the off-axis attenuation of the cardioid microphones together with the 20 cm spacing. If used at larger distances to the sound source the DIN stereo technique will lose the low frequencies due to the influence of the proximity effect on these types of microphones. The DIN stereo technique is more useful at shorter distances, for example on piano, small ensembles or used for creating stereo on an instrument section in a classical orchestra.

DirectSound

First introduced by Microsoft in Windows 2000, DirectSound is an API that adds an additional software layer between applications and the sound hardware. This layer uses today's high-speed CPUs to mix all waveform sounds before they go to the soundcard. This means that you could have a basic, two-channel soundcard, yet any number of applications could be producing sounds, and you would hear all of them. DirectSound enables the playing of sounds with very low latency and gives applications a high level of control over hardware resources. By using the DirectSound interfaces in music applications, you can do the following:

* Play sounds from files or resources in WAV format.

* Play multiple sounds simultaneously.

* Assign high-priority sounds to hardware-controlled buffers.

* Locate sounds in a customizable 3-D environment.

* Add effects such as echo and chorus, and change effect parameters dynamically.

* Capture WAV sounds from a microphone or other input.

Diversity Receiver

In wireless microphone applications, diversity receivers are often used to improve reception of RF signals. A diversity receiver utilizes two separate, independent antenna systems. The receiver looks at the signal coming in from the each antenna, and determines which one is the stronger. It then switches to that stronger signal. The receiver is constantly comparing to see which antenna is providing the better signal, and can quickly switch from one to the other as signal strength changes.

Ducker/Ducking

A dynamics processor/process that lowers (or "ducks") the level of one audio signal based upon the level of a second audio signal. A typical application is paging over background music: A ducker senses the presence of audio from a paging microphone and triggers a reduction in the output level of the music signal for the duration of the page signal. It restores the original level once the page message is over. Most dynamics processors (usually compressors are used) that give the user access to the detector circuit can be used for ducking. It is simply a matter of routing a copy/split of the second audio signal (the page in the example above) to the detector input such that it will trigger the gain cell to lower the level of the main signal (the music).

Dynamic (Microphone)

A dynamic mic is one in which audio signal is generated by the motion of a conductor within a magnetic field. In most dynamic mics, a very thin, light, diaphragm moves in response to sound pressure. The diaphragm's motion causes a voice coil which is suspended in a magnetic field to move, generating a small electric current. Generally less expensive than condenser mics (although very high quality dynamics can be quite expensive), dynamics feature quite robust construction, can often handle very high SPLs (Sound Pressure Levels), and do not require an external power source to operate. Because of the mechanical nature of their operation, dynamic mics are commonly less sensitive to transients, and may not reproduce quite the high frequency "detail" other types of mics can produce. Dynamic mics are very common in live applications. In the studio, dynamics are often used to record electric guitar and drums.

EIN

Abbreviation for Equivalent Input Noise. EIN is a specification we most commonly encounter when looking at microphones and preamps. Because the output of most microphones is so low the amount of self-noise they produce can be important. Apply a lot of gain and any little bit of noise becomes pronounced. Further, any self-noise of the preamp also becomes pronounced under the high amounts of gain required. There are established theoretical noise floor limits for electronic equipment. All devices operating at a temperature above absolute zero produce their own noise. Even a simple resistor, or any source of resistance in a circuit will produce noise. In fact, a 200 ohm resistor on its own produces 0.26 microvolts of noise. Referenced to standard line level signals this is equal to -129.6 dBu of noise (for more on dBu, see our Summit on dBu versus dBV). When a microphone is connected to a preamp you can think of the microphone as a 'source resistance.' 200 ohms is often considered typical, though mics do vary quite a bit, however the EIN specification is supposed to be measured with a 200 ohm source impedance (for the sake of comparing apples to apples). So you start with .0.26 microvolts of noise, and then add whatever noise the preamp has and you get the real working noise of the system (the system being the mic and the preamp). Preamp manufacturers know they are more or less starting at this theoretical noise limit (-129.6 dBu) so the value they quote is Equivalent Input Noise in their specs. EIN basically takes this 'source noise' into account. Therefore the theoretical lowest EIN spec you could encounter with preamps is -129.6 dBu, which would mean the preamp itself produces no noise at all. If the preamp produces the same amount of noise as the source resistance this value will go up by 3 dB to -126.6 dBu (you may also see dBm). Most mic preamps fall somewhere within this range, however, like most things in specs it is fairly easy for the manufacturer to tinker with the methods to produce better results. Consequently it is not unheard of to see values in the -130 to -135 range. This is usually accomplished by measuring with a lower source impedance, or even a direct short across the input. Resistors of lower impedance will produce less noise, but also offer an unrealistically low source impedance to the preamp, which means the measurements don't have as much 'real world' relevance. Occasionally you will see EIN rated in dBV. Be careful there because the dBV standard gives a result that is 2.2 dB better just because it is referenced to a different voltage to begin with (again, see the dBu versus dBV summit). Clearly this information is pretty technical and not for everyone. For those who don't want to digest it all you can sleep at night knowing that most modern preamps you encounter are of such high quality that they are within a tolerable range in terms of their self-noise. In short, don't lose too much sleep over this unless you are recording very low volume sounds.

Electret

A type of microphone design, similar to condenser. Basically, there is a permanently charged plate in the mic element. As the diaphragm moves in response to sound pressure, it creates a changing capacitance with the plate. The big advantage to using electret (also called back-electret, or occasionally prepolarized condenser) technology is that it does not require an external polarizing voltage (battery or phantom power). In some cases, the microphone includes an impedance changing preamp that requires battery or phantom power, but the electret element itself does not require voltage. Electret mics can lose their charge in high humidity and high temperature environments, so some care should be used in storing and using them. If the electret loses charge, the mic's sensitivity will suffer, resulting in an reduced signal to noise ratio.

Equivalent Input Noise (EIN)

A rating of the overall noise performance of an amplifier (typically a microphone preamplifier). Basically, this is a measure of how much noise a mic preamp will add to a microphone's signal. Measurements are normally made with a 150 Ohm resistor on the preamp to simulate the load a mic would present. The theoretical limit on EIN is -130.0 to -131.8 dBm (the thermal noise generated by the resistor). When comparing this spec, keep in mind that larger negative values are better (i.e. -124 is better than -118). But don't place TOO much weight on this spec, most current EIN specs are infinitesimally small (can you REALLY hear the difference between -120 dBm and -122 dBm??)

Feedback

Literally the return of a portion of the output of a process or system to the input. In our discourse (of audio and video production) we mostly encounter feedback when an open microphone is picking up sound from a nearby loudspeaker that is also being used to amplify sound from the same microphone. This forms what is known as a feedback loop. The sound of the room enters the microphone and is then amplified by the speaker. This amplified sound then becomes part of the sound of the room entering the microphone, which causes it to get amplified by the speaker again. If too much of this "feedback" occurs the signal will "run away" and quickly degrade into an oscillation at some frequency. This sound is the "squeal" we've all come to know and hate and is what we typically call feedback (though technically feedback occurred well before the squeal happened). It is also possible to produce electronic feedback. Routing the output of a mixer or effect unit back to its input is a sure way to do this. In fact, many effects are based on using this phenomenon creatively, the most obvious one being an echo with multiple repeats. Feedback and "feedback loops" are also used in all kinds of electronic circuits to achieve specific results. Old analog oscillators are based on electronic feedback.

Field Effect Transistor (FET)

A particular type of transistor, an FET behaves in a similar fashion to a triode (tube). There are actually several types of FETs, a common one in the pro audio world being the MOSFET (Metal Oxide Field Effect Transistor). FETs have a high input impedance, and respond in a linear fashion. This makes them ideal for condenser microphone preamps, as well as for certain power amplifier designs.

Figure 8

A microphone polar pattern in which the mic is (nearly) equally sensitive to sounds picked up from front and back, but not sensitive to sounds on the sides. This produces a pattern that looks like a figure 8 on paper, where the microphone is at the point of crossover on the 8. The pattern is also known as bi-directional.

Front Address

A microphone term that describes the perpendicular position of the diaphragm in relation to the body of the mic. In general, you sing, speak or play into the "end" of a front address microphone. Typical front address mics include the Shure SM57 and SM58 dynamic mics. Most hand-held vocal microphones have a front-address orientation. A common alternative, often found in the recording studio, is the side address mic, such as the Neumann U87.

Gain Before Feedback

An often not very scientific measure of how loud a sound reinforcement system can be turned up before any open microphone(s) will feed back. The point at which feedback occurs is effected by numerous variables, including atmospheric conditions (temperature, humidity, etc.) so it's not something that anyone considers an objective measure of performance. Instead the phrase is used to state relative differences: "By adjusting the EQ I was able to get 'more' gain before feedback."

Gap

In dynamic transducers such as most loudspeakers and dynamic microphones, the gap is a narrow circular trough in a magnet assembly in which the voice coil resides. The voice coil is attached to the cone of the speaker or mic diaphragm. In the case of a loudspeaker the voice coil becomes energized with electricity from an amplifier, which creates a magnetic field of varying polarity, which causes it to move in and out of the gap, thereby moving the speaker. In the case of a dynamic microphone the action is the opposite: acoustic energy moves the diaphragm, which causes the voice coil to move in and out of the magnetic gap, which generates an electrical signal that can be amplified.

GoBo

Short for "Go-Between." A gobo basically forms a type of barrier: sometimes this can be between a light source and an area to be lighted where you want to keep the light off of part of it, or it can be to form a barrier for sound such that a particular sound source is shielded from a microphone during recording. Gobos are often used in recording studios for just this purpose. Say you have an acoustic guitar and a drum set in the same room. In order to help reduce the amount of drums bleeding into the acoustic guitar mic sound, absorbent panels, or gobos, are place between the drums and the guitar mic.

Gooseneck

A flexible, spiral, metal coupling usually between 8 and 18 inches long that can be used to attach a microphone to a stand. The gooseneck is flexible and allows the microphone to be oriented in almost any direction. Most metal goosenecks squeak when moved so it is generally not possible to move them while the microphone is in use. Recently, however, manufacturers have started using rubber and plastic compounds to build goosenecks that can be move without generating excessive noise in the microphone.

Handling Noise

A specification for quantifying the sensitivity of a microphone to movement and shock. Handling noise is expressed as an equivalent sound pressure level as is a function of the construction of the microphone. This is an often overlooked concern when choosing a microphone as there can be vast differences in handling noise between two otherwise similar mics. Some manufacturers actually employ internal shock mounting devices to reduce handling noise.

Hi-Z

As the letter Z is the commonly agreed upon abbreviation for impedance, then Hi-Z simply refers to “hi-impedance.” This refers to the input or output impedance of a device (in our cases an audio device). Precisely what Hi-Z means, and how it is applied in the audio industry, is not entirely concrete. In general devices with impedances up through 600 ohms are said to be “low impedance,” while devices with impedances of several thousand ohms and up are considered “high impedance.” Typically we only come in to contact with these generic terms on microphones (usually low cost microphones), some direct boxes, and certain types of line inputs (on mixing boards, some tape decks, etc.). A typical guitar, for example, generally needs to be connected to a Hi-Z input. Otherwise the electronics will be “loaded down” and the sound will be significantly altered. A Hi-Z microphone – which we don’t encounter very often in pro audio (we generally use low impedance mics) – definitely needs to be connected to a high impedance input, and even then the cable length can’t be more than 10 or 20 feet before the signal degrades.

Hypercardioid

A polar pattern name typically used to describe microphone pick up characteristics. Hypercardioid patterns are similar to cardioid patterns in that the primary sensitivity is in the front of the microphone. They differ, however, in that the point of least sensitivity is at the 150 - 160 and 200 - 210 degree positions (as opposed to directly behind the microphone in a cardioid pattern). Hypercardioid microphones are thus considered even more directional than cardioid microphones because they have less sensitivity at their sides and only slightly more directly behind. Hypercardioid microphones are frequently used in situations where a lot of isolation is desired between sound sources.

In Line Mixer

An audio mixer configured to be able to monitor multitrack tape returns through the same channels that are used for inputs from microphones, line input sources, etc (see WFTD In Line Monitoring). This is in contrast to a configuration known as a split mixer, which has separate inputs dedicated to tape sends and returns. In line mixers have the advantage of being able to be smaller and less expensive, since each channel does double duty. It can often be accomplished with a couple more knobs and switches on each channel strip. This can potentially be a drawback since resources such as EQ, aux sends, etc, may have to be split between the input signal and the tape return signal, however, in many practical applications this limitation isn’t considered a problem since a resource like EQ will be used on the input source during tracking and overdubs, and then can be devoted to the tape return on mixdown since the mic/line input portion of the channel won’t be active.

Inverse Square Law

Useful when setting up a microphone or speaker, the inverse square law states that, in a free field the intensity of sound drops by 6 dB for each doubling of distance from the source. Now, none of us ever work in a truly free field (no reflective surfaces), but for most applications these numbers are accepted as workable. In real world terms, this means that for each time you double the distance between your sound source and a listener or microphone, the power of the audio drops by 75% - a fairly significant amount! How much is this in terms of volume? Well, it depends on the source you consult, we've seen both 6 dB and 10 dB convincingly listed as doubling or halving the volume (let's just say it's subjective and leave it at that...) - regardless, 6 dB is a very noticeable drop in level! Consider this the next time you place a microphone or speaker: Rather than just cranking up or attenuating the mic preamp or amplifier level for gain control, look at the distance to your source...

Jecklin Disc

Jecklin Disc A specific type of baffled stereo miking technique based on use of high quality omnidirectional microphones. Inventor Jorg Jecklin, the former chief sound engineer of Swiss Radio, was impressed by the spatial qualities of binaural recording but he tried to find ways to overcome the necessity of small-diaphragm cardioid microphone use. So he replaced binaural recording's artificial head with a 12'' disc of about 3/4'' thickness, which had a muffling layer of soft plastic foam on each side. Then he took two free-field equalized omnidirectional mics and attached them to the disc in such a way that the disc was between them. The capsules were above the surface of the disc just in the center, 17 cm apart from each other and each pointing 20 degrees outside. The result was an amazingly well defined stereo image, with true side separation and natural sounding depth. Jecklin began referring to this as an "Optimal Stereo Signal" (OSS). Almost every Swiss studio, and many others in Europe, uses an OSS disc for at least some stereo recording. Experiments with smaller-diameter discs proved unacceptable.

Large Diaphragm

Refers to the size of the diaphragm used in a microphone. Any microphone with a diaphragm larger than (and potentially including) 3/4" is considered to be a Large Diaphragm microphone. In general, Large Diaphragm microphones tend to have a "big" sound that engineers find especially pleasing where a little more character might be advantageous, such as is the case with most vocals. Large diaphragms are generally more sensitive than small diaphragm or medium diaphragm mics because of the increased surface area. A common myth is that large diaphragm mics capture more low frequencies than small diaphragm mics. Sometimes their coloration may make it sound like this is the case, but a properly designed small diaphragm mic is more likely to be accurate throughout a wide range of frequencies, whereas the coloration of a large diaphragm mic can tend to enhance certain desirable characteristics in a sound, which sometimes amounts to more apparent bass or low end.

Lavalier

A lavalier (a.k.a. Lapel Mic) is a small microphone designed to be worn on clothing or to hang around one's neck. They are used in applications where a large hand held microphone would either be too cumbersome or unsightly, or both. They are typically made with an extreme low frequency rolloff to reduce rumble and noise from moving against clothing.

Line Input

On mixing boards this is an input to a channel that is specifically designed for line level signals. Unlike the XLR microphone input, which is designed for low level mic signals, line inputs are usually 1/4 inch connectors, and are quite often unbalanced, though this will vary depending on the mixer. Line level signals are usually much higher than typical mic level signal and do not need as much amplification to be dealt with by the rest of the mixer. As such, on some mixers, the line inputs actually bypass the microphone preamp stage providing for a pure signal path into the board. Regardless of this, however, line inputs are always capable of handling higher level signals and high impedance signals better than the XLR mic input.

Lobar Polar Pattern

A type of polar, or pickup pattern found in many shotgun microphones. A microphone with a lobar polar pattern has the highest possible directivity. Lobar polar pattern is often referred to as: Supercardioid/Lobar, or Hypercardioid/Lobar polar pattern, but both Supercardioid and Hypercardioid patterns are slightly less directional than the lobar pattern. A lobar pick-up pattern is achieved with a shotgun microphone only.

Lobe

In acoustics and wireless communications, a lobe pertains to a pattern of transmission (in wireless systems and speakers) or pickup (microphones) that is not spherical, or omnidirectional. Essentially the lobe is the portion of a directional pattern bounded by one or two cones of nulls where there is little or no pickup or transmission. For example, a microphone with a figure 8 pickup pattern has two lobes in its pattern, one on each side of the mic. A hypercardioid mic also has two lobes, it's just that the front (desired) one is much more pronounced than the rear. A cardioid mic generally has one big lobe. As soon as you concentrate the energy of any transmission in a particular direction you create one or more lobes by definition. Wireless systems that use directional antennas also have this type of lobing, and so do loudspeaker systems. The characteristics of most lobes will vary by the wavelength of the sound or electromagnetic energy being radiated.

M-S Stereo

Abbreviation for Mid-Side, a method of stereo miking and recording. MS recordings capture the relative intensity of different sounds across the stereo soundfield. In order to make an M-S recording one must deploy a cardioid pattern mic facing the sound source(s) and a figure 8 pattern positioned sideways to the source. The figure 8 mic is connected to two channels of the mixer, with one channel having its polarity reversed. Each of the two signals (one of which is polarity reversed) of the figure 8 mic, when combined with the signal from the cardioid mic produces either a left or right "image" that is roughly equivalent to two cardioid mics positioned with a 90 degree angle between them. The only advantage to the MS method is the user can alter the width of the stereo image by varying the relative levels of the two microphones. There are several disadvantages, most of which are a function of having two dissimilar mics reproducing the same signal. Of course they can't occupy the exact same space either, which produces other phase and frequency response anomalies.

Maximum SPL (Sound Pressure Level)

A common specification for microphones, max SPL indicates the highest sound pressure level a mic's electronics can handle before the onset of distortion. Normally, this spec is referenced to 0.5% distortion at 1 kHz. Keep in mind that the presence of an attenuator switch on the mic may allow an increase in the volume level the mic can absorb before distorting.Obviously, this is an important spec for many applications - if the mic is going to spend its life in front of a screaming Marshall stack, or in a kick drum, it must be able to adequately deal with the volumes it will be seeing...

Medium Diaphragm

Refers to the size of the diaphragm used in a microphone. The definition of Medium Diaphragm is a potentially controversial subject. Historically there have been large diaphragm and small diaphragm mics, but more recently the medium size has began to carve out its own category, though not everyone agrees on the precise upper and lower limits. Most professionals and manufacturers agree that any microphone with a diaphragm near 5/8" to 3/4" can be characterized as a Medium Diaphragm microphone. Generally speaking, Medium Diaphragm microphones tend to do a decent job of accurately catching transients and high frequency content (as a small diaphragm would) while delivering a slightly fuller, round and potentially warmer sound (as a large diaphragm might).

Mic Amp

A type of amplifier specifically designed to amplify signals from microphones. Mic amps come in all shapes and sizes. Usually there are several built in to most mixing boards, but there are hundreds of different outboard units as well. Mic amps are often referred to as preamps, or mic preamps. Either way they are designed to work with the relatively low level and potentially fragile signals produced by microphones (see WFTD Mic Level). Since there are so many different types of mics (condenser, moving coil, ribbon, etc.) signal levels and impedances can vary widely. Besides sounding better in general, a good mic amp is better equipped to maintain the integrity of the signal under these widely diverse conditions.

Mic Level

The level (or voltage) of signal generated by a microphone. Typically around 2 millivolts. Compare this with the two normal line levels (1.23 volts and .316 volts), and it becomes apparent just how much amplification is going on in a microphone preamp, and why it is essential that preamps be of as high quality as possible!

Microphone

In honor of Microphone Month... Microphone - The word "microphone" comes from the Greek words "micro", meaning "small", and "phone" meaning "voice". A microphone is a transducer, or instrument whereby sound waves are caused to generate or modulate an electric current usually for the purpose of transmitting or recording sound. In all microphones, sound waves are translated into mechanical vibrations in a thin, flexible diaphragm. These vibrations are then converted by various methods into an electrical signal.

Minimum Terminating Impedance

The lowest impedance at which a piece of gear, usually a microphone, can effectively drive a signal into without degradation in performance. If the unit is connected to something with a lower impedance spec, it will usually have a lower output voltage or greater distortion or both. As it relates to microphones and preamps, this does not necessarily imply a bad, or undesirable resulting sound.

Mix-Minus

A specialized matrix-mixer where there is one output associated with each input that includes all other inputs except the one it is associated with. (The output is the complete mix, minus the one input.) In this manner, the simplest mix-minus designs have an equal number of inputs and outputs (a square matrix). For example, if there were 8-inputs, there would be 8-outputs. Each output would consists of a mix of the seven other inputs, but not its own. Therefore Output 1, for instance, would consist of a mix of Inputs 2-8, while Output 2 would consist of a mix of Inputs 1 & 3-7, Output 3 would consist of a mix of Inputs 1,2 & 4-7, and so on. Primary useage is large conference rooms, where it is desireable to have the loudspeaker closest to each microphone exclude that particular microphone, so as to reduce the chance of feedback.

Moving Coil

A specific type of dynamic (as opposed to condenser) microphone design. Moving coil microphones are among the most commonly used in music and sound production. The ubiquitous SM-58 and SM-57 mics are examples of moving coil design. These mics work on very simple principles. In fact they work just like a speaker in reverse. The diaphragm has a coil of wire attached to its base. This coil is inserted into a magnetic gap. When changes in air pressure cause the diaphragm to vibrate in and out of the magnetic gap it generates an alternating current in the wire that represents the signal.Moving Coil is also one method used in making phonograph cartridges. Moving coil designs were all but replaced by moving magnet designs (same principle, but the magnet moves instead) in the 1970's. Moving coil phonograph cartridges have very low output (requiring a different preamp) and are very expensive compared to their moving magnet counterparts, but there are some sonic advantages to them including lower distortion and better frequency response.

Multi-Pattern

A feature of certain microphones where the polar pattern for the mic is selectable between more than one pattern, either by changing the setting with a selector switch or replacing the capsule of the microphone.

Multipattern

A type of microphone design where the user has access to more than one polar pickup pattern. In some cases as many as a dozen different patterns can be made in a microphone. This is accomplished by using more than one (usually two) elements and combining them in different ways. Mostly two cardioid pattern elements are used. By using different levels and phase relationships between the two, which is accomplished in the electronics of the microphone, it is possible to have them cancel each other in ways that produce pickup patterns ranging from omnidirectional, through figure-8, all the way to very directional supercardioid patterns.

Near-Coincident Pair

A stereo miking technique similar to coincident pair, although in this case the mics are set up with some distance in-between them. Depending on the specific technique (examples of this type are ORTF and NOS) the distance and the angle at which the two microphones are pointing will differ. This technique creates a more defined stereo image, although it may not sum to mono as well.

Neodymium

Pronounced NE - O - Dim - E - Um, and holding atomic number 60 on the periodic table of elements (Symbol = Nd), neodymium is a silvery rare-earth metal element most commonly used for coloring glass. However it is also sometimes used to make magnets. Neodymium magnets are often stronger than magnets made of other materials, and as such come in handy for the audio industry because they enable manufacturers to produce microphones, and/or speaker drivers that are more powerful for a given size. Neodymium based microphones, for example, may have 6 dB (or more) greater output than their non neodymium counterparts.

NOS

Like the ORTF method (WFTD 4/17/97), NOS, which stands for Nederlandshe Omroep Stichting (that's the Netherlands Broadcasting System for all you monoglots) is a stereo miking technique. The NOS method is to place two cardioid microphones 30 cm (11.811023622 inches) apart and angled at 90 degrees from one another. This method produces more ambience than a strict coincident placement of mics, and fewer phase problems than widely spaced pairs of mics. Try the NOS method when recording ensembles or group performances, as well as on acoustic instruments. The center image of the recording will be nice and strong, but with a good amount of subdued room sound blended in as well... (for further information on mic patterns and placement, see inSync TTOTD 3/25)

Off-Axis

Refers to an audio source that is not directly in front of a transducer, especially a microphone. This results in off-axis coloration; a distortion or change in the frequency response of the reproduced audio signal. Often this coloration is put to good use. For example, many engineers intentionally set up mics on guitar amps so that they are slightly off access to control the amount of high frequencies captured. A microphone will generally produce the "truest" results if it is used on-axis (oriented directly in front of the sound source).

Omnidirectional

Literally, from all directions. In audio, microphones are said to be omnidirectional if they can detect sound equally from all directions. Speakers are omnidirectional if they radiate sound in all directions equally; this tends to be the case with subwoofers and low frequency drivers. Low frequencies, in general, tend to be omnidirectional, versus high frequencies which tend to "beam" or be very directional.

On-Axis

In our business this generally refers to an audio source that is directly in front of a listener or a transducer such as a microphone. This is at the 0 degree axis in a polarpattern. A microphone will generally produce the "truest" results if the desired source is on-axis (oriented directly in front of the sound source), although some creative engineers have been known to get desirable sounds by using a microphone's off-axis response. For loudspeakers the meaning is similar - when the listener is directly on axis with a speaker he/she will be exactly in front of it. How a speaker's characteristi

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Part one ended kind of abruptly, so here's the rest.

Off-Axis

Refers to an audio source that is not directly in front of a transducer, especially a microphone. This results in off-axis coloration; a distortion or change in the frequency response of the reproduced audio signal. Often this coloration is put to good use. For example, many engineers intentionally set up mics on guitar amps so that they are slightly off access to control the amount of high frequencies captured. A microphone will generally produce the "truest" results if it is used on-axis (oriented directly in front of the sound source).

Omnidirectional

Literally, from all directions. In audio, microphones are said to be omnidirectional if they can detect sound equally from all directions. Speakers are omnidirectional if they radiate sound in all directions equally; this tends to be the case with subwoofers and low frequency drivers. Low frequencies, in general, tend to be omnidirectional, versus high frequencies which tend to "beam" or be very directional.

On-Axis

In our business this generally refers to an audio source that is directly in front of a listener or a transducer such as a microphone. This is at the 0 degree axis in a polarpattern. A microphone will generally produce the "truest" results if the desired source is on-axis (oriented directly in front of the sound source), although some creative engineers have been known to get desirable sounds by using a microphone's off-axis response. For loudspeakers the meaning is similar - when the listener is directly on axis with a speaker he/she will be exactly in front of it. How a speaker's characteristics change as the listener moves more off axis is an important part of the overall response.

On-Axis

In our business this generally refers to an audio source that is directly in front of a listener or a transducer such as a microphone. This is at the 0 degree axis in a polar pattern. A microphone will generally produce the "truest" results if the desired source is on-axis (oriented directly in front of the sound source), although some creative engineers have been known to get desirable sounds by using a microphone's off-axis response. For loudspeakers the meaning is similar - when the listener is directly on axis with a speaker he/she will be exactly in front of it. How a speaker's characteristics change as the listener moves more off axis is an important part of the overall response.

Op Amp

Short for Operational Amp, a circuit component used in all sorts of equipment. Though they are technically considered amplifiers they are quite often used in circuits that do not obviously "amplify" signals. Examples would be equalizers, crossovers, compressors, mixers, microphones, keyboards, effects and many, many, many more (the list is endless). Op amps acquired their name from early uses in analog computers (computers perform operations, get it?). They can exhibit very high gain and are extremely easy to build into audio circuits. Nowadays they are available in integrated circuit chips, each of which may have many op amps inside. In some cases they are literally a dime a dozen.

Open Mic

A microphone that is turned on and turned up, meaning it is entirely ready to be used, whether for recording or in a sound reinforcement application.

ORTF

A stereo recording method created by the French national broadcast system to simulate the directional perspective of human ears. Similar in approach to the more conventional X-Y configuration, two microphones are placed in front of a sound source. The mics are spaced 17 cm (about 6 3/4") apart, at an angle of 110 degrees. The ORTF method provides good mono compatibility and stereo imaging, but captures little of the room's ambience (this may or may not be a good thing, depending on the room you are recording!) Try this mic setup the next time you are recording a small ensemble, choir, orchestra, or even a solo acoustic instrument, it works quite well. For those who just HAVE to know what the acronym ORTF stands for, the answer is: "Office de Radiodiffusion-Television Francaise"...

Pad

1. An electronic circuit designed to attenuate the output of a device by a given amount. For example, some microphones have so much output that they can overdrive the input stage of many mic preamps. To prevent this, mic designers will include a switchable "pad" on the output stage of the mic, attenuating, or reducing the mic's output by 10 or 20 dB. While many devices have built-in pads, it is also possible to purchase external pads, which plug in to a device's output and reduce its level.

2. A sustainy, "wash" or fill sound, usually used as harmonic background material in a musical arrangement. Arrangers often speak of using a "string pad" during a passage; this would be a section of strings playing long, sustained chords behind the melody. With the advent of samplers and synthesizers, other types of sounds have also become common as pads; just about any sound that can sustain can be used as a pad these days!

Phantom Power

A DC (direct current) voltage, usually 48 volts, applied to pins 2 and 3 referenced to pin 1 of an XLR microphone connector that can be used to power transducers with active electronics. Condenser microphones require a pre amp close to the very high impedance (See WFTD archive "impedance") diaphragm which requires power to operate. Back in the '50's and '60's this power was often provided by a separate power supply that came with the microphone. Later manufacturers began to provide a source for this power at the microphone input to mixers or pre amps. Since the power is carried on the same wires that carry the audio signal, and since most dynamic microphones and other passive devices are not affected by this DC voltage it was known as "phantom" power. The theory was that only devices that needed it would be wired in such a way that they would use it. Nowadays almost all condenser microphones and active direct boxes are able to use phantom power when it is present on a microphone cable. Consequently most mixing board manufacturers include this feature in their products.

Phase Cancellation

Phase describes where in its cycle a periodic waveform is at any given time. The relationship in time of two or more waveforms with the same or harmonically related periods gives us a measurement of their phase difference. Phase cancellation occurs when two signals of the same frequency are out of phase with each other resulting in a net reduction in the overall level of the combined signal. If two identical signals are 100% or 180 degrees out of phase they will completely cancel one another if combined. When similar complex signals (such as the left and right channel of a stereo music program) are combined phase cancellation will cause some frequencies to be cut, while others may end up boosted. Phase and phase difference is a real-world issue in areas such as electrical wiring of audio equipment, signal path, and microphone placement during the recording process. Phase reversal can be a serious compromise of sound quality or a special effect affecting the perceived spaciousness of the sound depending on the context of its occurrence.

Piezo

Short for piezoelectricity or piezoelectric effect. Piezoelectricity is an electric charge that occurs in some substances when they are squeezed or otherwise subjected to mechanical stress. It is also possible to cause these materials to vibrate when a voltage is applied to them. Quartz is one of the better known piezoelectric materials, and is commonly fabricated into small pieces, called "crystals" that are used for frequency standards. A crystal of specific size and shape will vibrate at a predictable and very stable rate when a voltage is applied. This makes them ideal for use in things like watches or clocks for digital audio equipment. Piezoelectric elements have also been used various types of transducers such as phonograph cartridges, microphones and loudspeakers. Piezo microphones can be quite small and still have relatively high output at a low cost; however, their less than ideal frequency response prohibits use in critical applications. Piezo loudspeakers usually come in the form of tweeters, or very high frequency elements. They generally have very low distortion in the 5 kHz and above range, but haven't widely been used in sound reinforcement due in part to their relatively low output levels. It takes dozens of the average piezo tweeter to equal the output of one medium-sized compression driver.

Plate Reverb

A type of synthetic reverberation system. Plate reverbs were one of the first types of artificial reverbs used in recording. They used a steel plate under tension supplied by springs at the corners where the plate was attached to an outer shell. The plate gets vibrated in accordance with a signal from a transducer and the vibration is sensed elsewhere on the plate with a contact microphone of one type or another. Put your ear up to any large metal item and tap on it and you will hear how steel plates were used to create reverb. Plates were initially used a great deal in the early days of studio recording (even though they don't sound that much like natural reverberation) due to their relatively small size and low cost when compared to a reverberation room. While many other types of artificial reverbs appeared on the scene (spring, etc.) the plate reined king until the advent of digital reverbs. While in many cases early digital reverbs sounded even less like natural reverb than plates did, they did offer the function at a much lower price and in a much smaller package. Ultimately digital reverbs prevailed sonically as well, and even began to include plate simulations in their algorithms. Of course there are many engineers who still prefer the sound of a good old plate, just like they like other types of vintage equipment.

Plosive

A phenomenon that occurs when humans speak words that require a complete closure of the oral passage followed by the release of a burst of air. This commonly occurs in everyday speaking. Sounds like the "P" in the word "pit" or the "D" in "dog" will produce a sudden burst of air from the mouth. If you place your hand in front of your mouth and make these sounds you will feel the burst of air. These sudden movements of air can be a real problem for sensitive microphones recording vocals. To a microphone this mammoth air movement will sound like a loud, bassy pop or thumping sound. Pop filters are commonly used in recording sessions to reduce this problem.

Point-to-Point Wiring

A method of connecting electronic components in a microphone, preamp, amplifier or any other piece of equipment in which each component is directly soldered to a tube pin or solder lug or jack. This is essentially the "original" method of making solder connections, which in modern times has largely been replaced by the use of printed circuit boards, on which the wiring has been replaced by conductive traces (usually copper or silver) that run from socket to socket as required for connections. Original forms of point-to-point wiring used no "boards" whatsoever; key components such as vacuum tubes were often mounted in ceramic sockets for stability. A variation on this employed the use of tag boards - simple templates, often made of thin cardboard with a waterproof coating - on which the location of each component was marked or stamped, to speed assembly. Virtually all soldering performed in point-to-point wiring was (and is) done by hand.

Polar Pattern

Depending on their design and construction, microphones respond to sound coming from different directions with varying degrees of sensitivity. A plot or graph of this response is called a polar pattern (sometimes polar response curve). Looking at a mic's polar pattern will tell you how directional it is, how well it will reject sound from certain directions, etc. It is important to note that polar patterns are frequency dependent. Typically, low frequency response will be almost omnidirectional; the polar pattern will be come more directional as frequency rises.

Polarize

Placing a constant (usually DC) voltage across a device or circuit is said to polarize it. For example, condenser microphones require a polarization voltage to charge the capacitive element so they can operate.

Pop

A bassy thump or "explosive" sound heard in a vocal mic (this is called a "plosive"). Pops often occur when the vocalist pronounces words with "p", "t", "b", etc. sounds in them. These consonants can create a puff of air that strikes the microphone diaphragm, creating a thump in the audio signal. In general, windscreens will help with pops to an extent, but a pop filter will be more effective. Be careful that the pop filter you choose is transondent (see WFTD archive), and serves only to break up the plosive's effects.

Pop Filter

A pop filter is used with microphones to shield the diaphragm from sudden bursts of sound which can cause a popping (see WFTD archive "pop") effect. The shield is transondent (see WFTD archive "transondent") and does not interfere with the movement of sound towards the microphone. Pop filters, which usually look like a 6" to 8" circle of mesh material, are commonly seen in recording studios situated between 1" and 8" in front of a microphone.

Potential Acoustic Gain

A measure of the amount of gain before feedback that can be obtained with a sound reinforcement system that's based on the number of open microphones and distances from source(s) to microphones and listener(s), as well as speaker distances from listener(s) and microphones. These parameters are basically plugged into an equation that involves the application of the inverse square law. A typical equation might look like:PAG = 20 log (D1) - 20 log (D2) + 20 log (D3) - 20 log (D4) - 10 log (NOM)where,PAG = Potential Acoustic GainD1 = Distance between microphone and loudspeakerD2 = Distance between the loudspeaker and the furthest listenerD3 = Distance between the source and the furthest listenerD4 = Distance between the source and the microphoneNOM = Number of open microphonesThere are a number of subtleties to the application of this formula (what you see here is somewhat simplified) that are beyond the scope of this writing, but when applied correctly it can yield a pretty accurate estimation of the performance of a system.

Potting

The term "potting" refers to the sealing of pickup coils in a solid material. Potting stabilizes the components of the pickup so that they cannot move relative to each other. This eliminates vibration-induced signals that make a pickup act like a microphone causing unwanted feedback. Potting can also protect the inner coil from corrosion. The best technique for potting also includes "coil immersion." Coil immersion is allowing a solid (wax) to be absorbed into the coil. Wax is used because it works well, is inexpensive, and it makes it possible to work on the pickup later. A correctly potted pickup coil will have the wax absorbed throughout the coil as well as the surrounding parts such as magnets, pole-pieces, and metal covers. This eliminates movement of parts inside the pickup.

Preamp

Short for preamplifier. A type of amplifier specifically designed to amplify very weak signals before they are fed to subsequent gain stages or devices. Preamps are commonly used to bring things like the output of microphones up to a level where more equipment can work with the signal. Similarly, magnetic pickups (as used in guitars and basses), and phonograph cartridges are generally run through a preamp to prepare the signal to be used by other equipment downstream. Preamps are called upon to deliver extremely high amounts of gain while introducing very low amounts of noise and distortion. As such they are a critical component in the audio chain, and in recent years have come under much scrutiny by recording engineers causing many dozens of stand-alone mic preamps to be developed that allege to have superior sonic characteristics.

Prepolarization

A technique of depositing a fixed charge-carrying layer on either the diaphragm or backplate of a condenser microphone, thus eliminating the need for an external polarization voltage. Such microphones are termed "prepolarized condenser microphones" or "electret microphones".

Pressure Microphone

A microphone in which only one side of the diaphragm is exposed to the impinging sound. The diaphragm responds to the pressure variations uniformly and therefore pressure microphones are inherently omnidirectional. Also sometimes called "pressure operative microphone".

Pressure-gradient Microphone

A microphone in which both sides of the diaphragm are exposed to the incident sound. The microphone is therefore responsive to the pressure differential (gradient) between the two sides of the membrane. Sound waves parallel to the plane of the diaphragm produces no pressure differential, and so pressure-gradient microphones have figure-eight directional characteristics. These are also sometimes called "velocity microphones", since the output voltage is proportional to the air particle velocity.

Proximity Effect

An increase in bass or low frequency response when a sound source is close to a microphone. Proximity effect is distortion caused by the use of ports to create directional polar pickup patterns, so omni-directional mics are not affected. Depending on the mic design, proximity effect may easily result in a boost of up to 16 dB, usually focused below 100 Hz. Vocalists tend to like proximity effect since it fattens up their voice, but a constantly varying bass boost can wreak havoc on headroom and carefully set levels! Obviously, if a vocalist is "eating the mic" to get proximity effect, the Inverse Square Law (WFTD 6/12) tells us that the levels the mic sees are increasing dramatically as well - distortion can easily result, from either mic diaphragm breakup or electronic overload. (You may occasionally see proximity effect referred to as "bass tip-up")

PZM

Many of our recent Piano Miking Suggestions recommended use of PZM microphones. PZM (Pressure Zone Microphone), or more correctly boundary mics (PZM is a trademarked term) use a small electret capsule mounted close to a backing plate. The idea is that the mic capsule/plate is mounted to a large flat surface (or boundary). This increases the sensitivity of the mic by 6 dB (due to pressure doubling from reflected soundwaves), and gives it a hemispherical pickup pattern. The practical frequency response of the mic will depend on the size of the flat surface it is mounted to. If the surface is too small, low frequencies will not be reflected resulting in an apparent high frequency (treble) boost.

Reverb

The remainder of sound that exists in a room after the source of the sound has stopped is called reverberation, sometimes mistakenly called echo (which is an entirely different sounding phenomenon). We've all heard it when doing something like clapping our hands (or bouncing a basketball) in a large enclosed space (like a gym). All rooms have some reverberation, even though we may not always notice it as such. The characteristics of the reverberation are a big part of the subjective quality of the sound of any room in which we are located.Our brains learn to derive a great deal of information about our surroundings from the sound of a room and it's reverberation. Consequently it is necessary to have the proper type and amount of reverberation on recordings in order for them to be aesthetically pleasing or to sound natural to us. This can be accomplished with careful microphone placement, but it is often necessary to employ artificially created reverb.To create reverb, a device known as a reverb unit is employed. Reverb units have historically come in many shapes and sizes, and have used many different techniques to create the reverberation. These days most of the reverb units employed throughout the world are digital, where the sound of the reverb is generated by a computer algorithm and mixed with the original signal. We will be discussing other types of reverb units in the future.

Ribbon Mic

A type of velocity microphone. A velocity microphone responds to the velocity of air molecules passing it rather than the Sound Pressure Level, which is what most other microphones respond to. In many cases this functional difference isn't important, but it can certainly be an issue on a windy day. Very old ribbon mics could be destroyed from the air velocity created just by carrying them across a room. A ribbon mic works by loosely suspending a small element (usually a corrugated strip of metal) in a strong magnetic field. This "ribbon" is moved by the action of air molecules and when it moves it cuts across the magnetic lines of flux causing a signal to be generated. Naturally ribbon mics have a figure 8 pick up pattern. You can think of it like a window blind; it is easily moved by wind blowing at it, but usually doesn't move when wind blows across it from left to right. Ribbon mics were the first commercially successful directional microphones.

Ring Out

Refers to a process of tuning a PA or monitoring system involving the intentional initiation of feedback to locate sensitive or hot frequencies. Monitor systems are most prone to feedback at frequencies where the speakers and/or open microphones have peaks in their frequency response. One can quickly find these peaks by turning up the volume on the mics in question until feedback begins. This is usually where equalization is applied to counteract troublesome frequencies - i.e. if it feeds back at 4 kHz then pull 4 kHz down on your EQ a few dB. Four or five rounds of this is usually enough to get rid of the major problems. While this technique is commonly used for stage monitoring systems, it can also prove surprisingly effective for the FOH system as well, particularly in situations where there is a heavy emphasis on vocal reproduction.

Sensitivity

In audio terms, sensitivity is the minimum amount of input signal required to drive a device to its rated output level. Normally, this specification is associated with amplifiers and microphones, but FM tuners, phono cartridges, and most other types of gear have a sensitivity rating as well. In general, higher sensitivity is better (less input signal required for full output), but there are definitely situations where a device can be TOO sensitive (picture a very sensitive microphone in front of a wound-up Marshall guitar amplifier!) resulting in unwanted distortion.

Shockmount

Commonly found in two places in the audio industry, rack cases and microphone stands, shockmounts are systems designed to isolate a device mechanically from its stand or case. In rack cases, the idea is to prevent damage to sensitive gear by isolating it from shipping and transport bumps, drops and similar catastrophes. Often these cases consist of a case-within-a-case, with the inner case isolated with foam or spring arrangements from the outer. Microphone shockmounts are designed to reject vibrations transmitted through the stand or boom to the microphone. Several types are in use, one common design using a system of "rubber-bands" to suspend the mic away from its stand.

Shotgun Microphone

A type of microphone characterized by an extremely directional polar pattern. Shotgun mics may be condenser or dynamic, but are almost always built with a long (8 to 24 inch) tube protruding from the front. This tube has a series of holes or slots along the side, which act as a phase canceling device for sounds coming from the rear of the microphone. Sounds coming from directly in front of the mic enter each of the holes or slots in succession and therefore add in phase by the time they reach the diaphragm. Sounds from the rear enter in reverse order and thus are out of phase when they reach the diaphragm, resulting in little or no output. The longer the tube the more directional the microphone becomes. These properties make them ideal for pinpointing and capturing the audio of something from far away without capturing as much of all the ambient (or surrounding) sound. Shotgun mics are sometimes called Line Microphones.

Shuffler

A simple circuit used for enhancement of space or stereo width in recording. The shuffler, (first described by Blumlein) is the basis for MS microphone decoding to stereo, as well as the circuit used to create FM signals. The shuffler takes the left and right signals of the stereo pair and mixes them into two separate signals, one being the sum of the signals (A+B), the other being the difference (A-B). While they are in this format, we can apply processing to either signal (A+B or A-B), and then convert them back into stereo. A mixing console with polarity invert switches on the channel strips can be used to create a shuffler. The A+B signal is easy to create (it's just the sum of the two); the A-B signal is created by combining the two while the polarity is reversed on B.

Side Address

A microphone term that denotes the parallel position of the diaphragm in relation to the body of the mic. A side address microphone accepts sound from an angle perpendicular to the mic as opposed to a front address mic where you speak into the "end" of the microphone. A good example of a side address microphone is the C414 by AKG. There is generally a front and back side to any side address mic, and in many cases usable sound can also be picked up from the backside.

Signal Path

Simply the route a particular signal takes through a chain of equipment and/or electronic components on the way to its destination. When we think of signal paths in audio we are usually thinking about connecting different pieces of equipment together and routing some signal(s) through them. An example of this would be something like a microphone to mixer to speaker or recorder setup. The signal path has the signal from the microphone pass from the microphone through those (and potentially other) devices on the way to being recorded or amplified (or both). But there is also a signal path inside each piece of equipment. A mixer may be configured to route signals in different ways internally bypassing or utilizing different gain stages along the way to achieve different results. Effects processors often have highly configurable internal signal paths depending upon what they are doing.

Small Diaphragm

Refers to the size of the diaphragm used in a microphone. While there are no final standards regarding a diaphragm size that defines Small Diaphragm, most professionals and manufacturers agree that any diaphragm smaller than 5/8" would be considered a Small Diaphragm. Generally speaking, Small Diaphragm microphones tend to do a good job of capturing high frequency content and transients. They will tend to have a bit more "air" to their sound and often have less coloration than medium diaphragm or large diaphragm microphones. Most of this is due to the reduced mass of the smaller diaphragm, which allows it to more closely follow any air disturbances it is subjected to.

Sound Card

An expansion board that enables a computer to manipulate and output sounds. Sound cards have become commonplace on modern personal computers and are typically associated with the consumer market. Sound cards enable the computer to output sound through speakers connected to the board, to record sound input from a microphone connected to the computer, and manipulate sound stored on a disk. Some sound cards also support MIDI, surround sound and more. In addition, most PC sound cards are Sound Blaster- compatible, which means that they can process commands written for a Sound Blaster card, a standard in consumer PC sound.

Spaced Omni

A method of stereo recording where two omnidirectional microphones are placed several feet apart in front of the sound source. This system was used by Harvey Fletcher in 1933 in the first demonstration of stereophonic reproduction of an orchestra. Because the omni pattern will pick up room ambience as well as the desired sound source, mic placement is critical in balancing room sound with direct sound. And, as with any stereo miking technique, phase must also be considered when placing the mics. Spaced omnis are excellent where a natural, "real" sound is desired.

Sputter/Sputtering

In physics, a process whereby atoms of a solid - usually a metal - are added to or removed from some surface. There are a variety of industrial applications. In audio sputtering is often used to apply a molecular layer of gold to the surface of microphone diaphragms and some electrodes to improve conductivity.

Squelch

A function found on some radio receiving systems such as wireless microphones and guitar units that allow the user to set the receiver to mute or gate itself when the carrier falls below a specified level. The idea is to eliminate the unwanted noise associated with a radio receiver being tuned between stations, or not properly picking up a station/transmitter to which it is tuned. Typically turning the squelch control "up" makes the receiver have more of a tendency to mute, which means the carrier strength has to be higher in order for it to operate. If the squelch is set too high the audio will mute from time to time, however, if it is set too low you run the risk of getting blasts of noise through the system when the signal strength is compromised for one reason or another. The squelch control was an important part of wireless systems for many years, but with modern technology there are more sophisticated and automated methods of handling these things, which have all but eliminated the manual squelch control from systems.

STC

Abbreviation for Sound Transmission Class. This is a number rating that can be used to compare, in a generalized way, the acoustical isolation of different barrier materials or partition constructions. Higher numbers indicate a material will provide more acoustic isolation when used as a barrier. The tests conducted to determine STC involves two test rooms: a ''source'' room and a ''receiver'' room. The source room will contain a full-range test loudspeaker. The receiver room will contain a microphone, which is connected to sound-measuring devices. There is a nominal opening between the two rooms - usually about 9' wide by 8' high, but can vary in accordance with the standard. The first step is to measure the sound transmitted from one room into the other through the opening. The sound is measured in decibels (dB) in 1/3-octave bands from 125 Hz to 4000 Hz. Then the opening is plugged with the material or partition construction. This could be a single layer of barrier, such as plywood or drywall, or a complete wall with as many materials, layers, air gaps, etc. that can fit in the opening. The edges are completely sealed and sound transmission between the rooms is measured again. The sound level from the ''after'' test is subtracted from the sound level ''before'' plugging the opening. The resulting difference is known as the transmission loss or ''TL.'' Next, the TL is plotted on a graph of 1/3-octave band center frequency versus level (in dB). To get the STC, the measured curve is compared to a reference STC curve. Two criteria are used to ''match'' the curves: 1. The reference curve shall not exceed the measured TL by more than 8 dB in any 1/3 octave band, and 2. The sum of all the ''negative discrepancies'' shall not exceed 32. (This actually sounds more complicated than it is. A simple spreadsheet can be used to calculate the STC for any range of TL values.) Once the two above criteria are met, the value of the reference curve at 500 Hz is read as the entire STC of the material or partition type.

Stereo Bar

A device for mounting two microphones on a single mic stand. They generally consist of a bar (sometimes adjustable in length) with a fixture to mount to a mic stand, and then two adjustable fixtures for microphones. Usually used for stereo recording, the stereo bar allows you the option of positioning the two microphones exactly as you wish to optimize the stereo image. Some engineers believe this approach introduces small timing differences into the recording due to the inherent imperfections of positioning the mics by hand, but it is a perfectly acceptable and time honored technique, especially if the microphones face outwards rather than inwards after you attach them to the bar and line them up. The timing differences that can occur stem from the fact that each microphone casts a sound shadow (literally, it physically gets in the way of the pickup pattern of the other) at high frequency, and if they face inwards this is likely to degrade the stereo image (particularly if the mics in question are physically large, such as AKG C414s, or Neuman U87s). If the mics face outwards, the sound shadow will fall on the rear of each microphone, where it is relatively insensitive (assuming the mics are set to cardioid, hypercardioid or supercardioid patterns) and will not cause imaging problems. Some stereo bars have detailed markings to aid the engineer in making fine adjustments to mix spacing and angle. A typical studio application using a stereo bar would be to place mics directly above the drummer, with the microphones angled down towards the drums and outwards at approximately 90 degrees from each other. This gives good separation and minimizes phase problems.

Supercardioid

A polar pattern name used to describe the pickup pattern of some microphones. The supercardioid pattern is very similar to, and often confused with, the hypercardioid pattern. The supercardioid pattern is slightly less directional than the hypercardioid pattern, but the rear lobe of sensitivity is also much smaller in the supercardioid.

Suspension Basket

A device for isolating a microphone from mechanical vibrations. A type of "shockmount." The most common way to shock mount a microphone is with the stand mounted suspension basket, which utilizes elastic bands to isolate a microphone from vibrations that can be induced into the stand through the floor or by something bumping the stand itself. Most mid to high price microphones have specific suspension baskets designed for them, and are available as an accessory.

Talkback

A feature offered on recording consoles, talkback is an in-board intercom system, allowing the engineer and producer in the control room to talk to musicians in the studio. Normally, there is either a built-in microphone for this purpose, or there is a dedicated talkback mic input. This mic/input is routed only to the cue/studio monitor sends, preventing feedback problems with the control room monitors.

Thermal Noise

Also called Johnson noise, is the random white noise found in any conductor or electronic device. It is produced by the thermal agitation of the charges in an electric conductor and is proportional to the absolute temperature of the conductor. It manifests itself in the input circuits of audio equipment such as microphone pre amps, where the signal levels are low. The thermal noise level is the limiting minimum noise any circuit can attain at a given temperature. Modern high-quality microphone pre amps, under proper conditions, have noise specifications that come very close to this theoretical limit.

Time Alignment

In a multiple driver loudspeaker system, it is important that the time delay inherent in each driver and its associated crossover network be the same to preserve accurate transient (see WFTD archive transient) response. In other words, the high frequencies and low frequencies much reach the listener's ear at the same time. A system which meets this criterion is said to be "time aligned." One way to accomplish this is to place the tweeter further away from the listener than the woofer, and this is done in many speaker systems. Another way is to design the crossover network to add a suitable delay to the high frequency signal before it gets to the driver.The phrase "time alignment" is also sometimes used in reference to adding delay to one or more microphones in a situation where more than one mic is being used on an instrument, and the mics are at different distances from the instrument. A good example of this is orchestral recording where several mics are employed at various distances to accurately capture the sound of the orchestra in the hall. The microphones closer to the orchestra are sometimes delayed to be more in "time" with microphones placed out in the hall."Time Alignment" was copyrighted as a trademark by a speaker manufacturer years ago and is no longer widely used as a generic term.

Transducer

For our purposes, a transducer is an electronic component that transforms one type of energy into another. Some examples: A microphone converts sound into electric current. Likewise, a speaker converts electric current into sound. Other common transducers include magnetic guitar pickups, piezo pickups, phonograph cartridges (remember those?) and tape heads. One of the main challenges we all face (whether we know it or not) is overcoming the physical limitations transducers put on our ability to reproduce the extremely wide dynamic range of acoustic sounds... deadly enemies of your gear!

Transformer

A transformer is a device consisting of two or more coils of wire wound on a common core of magnetically permeable material. The number of turns in one coil divided by the number of turns in the other is called the turns ratio. An alternating voltage appearing across one coil will be inducted into the other coil multiplied by the turns ratio. Some transformers are designed to operate at 60 Hz (see WFTD archive "Hertz") and to handle large amounts of current. They are called power transformers, and are found in almost all electronic equipment to change our 110 volt line voltage to one or more voltages more suitable for operating the device. Audio transformers are designed to operate at audible frequencies, and are used to step audio voltages up or down to send signals between devices such as microphones, tape recorders, mixers, and all types of other electronic equipment. Transformers are also sometimes used in audio to provide isolation between two audio circuits. Because the two coils of wire never electrically touch one another a transformer provides a certain amount of isolation that can help prevent ground loops and other problems that can crop up in complex audio systems.

Trim

Found on most mixers, trim controls provide the initial level setting for each channel's input gain. In most cases, trim adjusts gain of the microphone preamp, but it may also apply to line level signals. Optimizing this gain stage will make a tremendous difference in the mixers signal to noise ratio and in gain staging later in the signal chain.

True Diversity

A wireless microphone term. A more advanced form of a diversity receiver, a true diversity system contains a radio receiver that actually has two independent receiver sections, each with its own antenna (rather than a single receiver with one or two antennas), to pick up the transmission from a wireless microphone. The antennas are spaced apart on the unit, and by means of a comparison circuit the unit constantly polls the two receivers to select the one with the strongest signal. The result is an exceptionally stable signal, since the appearance of a dropout in both antennas at the same time is not likely under normal circumstances.

Unidirectional

With reference to microphones, the opposite of omnidirectional (see WFTD archive, "omnidirectional"). A unidirectional microphone is one which is more sensitive to sound from one direction than from others. The level of "unidirectionality" will vary with the mic's particular polar pattern (i.e. cardioid, hypercardioid, etc.). There is no such thing as a perfectly unidirectional microphone, but the more unidirectional a mic is, the better it is able to reject off-axis sound, producing more isolated signals.

Variable Pattern Mic

A microphone in which the polar pattern can be adjusted. The adjustment may be in the form of a switch that switches between two or more common patterns such as omnidirectional, cardioid, supercardioid, hypercardioid, figure-8, and possibly some settings in between, or it can sometimes be a knob that provides a continuous adjustment. In most cases a variable pattern mic is made by placing two condenser diaphragms back to back, and then regulating the way the signals from them are combined inside the mic. Depending upon the exact construction, and the quality (and matching) of components a particular pattern may not always behave in exactly the same fashion as a mic with a fixed pattern. Nevertheless they are very widely used because the flexibility and overall usefulness of having multiple patterns often outweighs any minor discrepancy in the accuracy of the polar pattern. In fact, some of these inconsistencies can work to an engineer’s advantage if he or she understands how to apply them.

Wind Screen

A device placed in front of or around a microphone to shield the mic element from wind. Wind screens are generally made of foam, or a foam-like material - something porous. The idea is for the device to allow sound to pass through without interference, but to limit larger pressure variations such as those caused by wind. Mic elements are necessarily sensitive to extremely small changes in air so they can pick up sound properly. Wind is interpreted by a microphone as a very, very large change in pressure - far beyond what it is designed to handle - thereby causing distortion either due to the element moving in a non-linear fashion and/or because the electronics driven by the output of the element distort. The result is a very unpleasant sound. When operating a microphone in windy conditions it is usually a good idea to employ a wind screen. Many professional microphones have wind screens made specifically for them and their shape, but it is not uncommon to use generic wind screens in some applications.

Wireless Receiver

A wireless system consists of two main components: a transmitter, and a receiver. The responsibility of the wireless receiver is to pick up the radio signal broadcast by the transmitter and change it back into an audio signal. Wireless receivers are available in two different configurations. Single antenna receivers utilize one receiving antenna and one tuner, similar to an FM radio. Diversity receivers, or dual antenna systems, often provide better wireless microphone performance. A diversity receiver utilizes two separate antennas spaced a short distance apart and (usually) two separate tuners. An "intelligent" circuit in the receiver automatically selects the better of the two signals, or in some cases a blend of both. Since one of the antennas will almost certainly be receiving a clean signal at any given moment, the chances of a dropout occurring are reduced. There are actually several distinctions among dual antenna systems (diversity, true diversity, etc.) that are variations on the same theme.

Wireless Transmitter

A wireless system consists of two main components: a transmitter, and a receiver. The transmitter handles the conversion of the audio signal into a radio signal and broadcasts it as a radio wave via an antenna. The antenna may stick out from the bottom of the transmitter or it may be concealed inside. The strength of the radio signal is limited by government regulations. The distance that the signal can effectively travel ranges from 100 feet to over 1,000 feet, depending on conditions and quality of signal. Transmitters are available in two basic types. One type, called a "body-pack" or "belt-pack" transmitter, is a small box about the same size as a pack of playing cards (or smaller in some cases). The transmitter clips to the user's belt or may be worn on the body. For instrument applications, a body-pack transmitter is often clipped to a guitar strap or attached directly to an instrument such as a trumpet or saxophone. In the case of a handheld wireless microphone, the transmitter is built into the handle of the microphone, resulting in a wireless mic that is only slightly larger than a standard wired microphone. Usually, a variety of microphone elements or "heads" are available for handheld wireless microphones. All wireless transmitters require a battery (usually a 9-volt alkaline type) to operate.

Xophonic

An artificial reverberation device made for the home by the Radio Craftsmen in the 1950's. Basically it was a box about the size of a bookshelf loudspeaker that contained a small speaker and about 50 feet of tubing with a microphone at the other end. This produced a time delay of about 50 milliseconds and this reverb was mixed in with the original signal and radiated in the room through a separate amp and speaker. The Xophonic may have been the very first signal processor designed for home use. It was popular for a short time before falling into oblivion with the advent of stereophonic sound reproduction.

XY Stereo

A stereo miking technique that employs two cardioid microphones angled 90 degrees from each other, but positioned at the same point (or as near as their physical size will allow). Theoretically, the two microphone capsules need to be at exactly the same point to avoid any phase problems due to the distance between the capsules. As this is not possible, the best approximation to placing two microphones at the same point is to put one microphone on top of the other with the diaphragms vertically aligned. In this way, sound sources in the horizontal plane will be picked up as if the two microphones are placed at the same point.The stereo image is produced by the off-axis attenuation of the cardioid microphones. While A-B stereo is a difference-in-time-stereo, the XY stereo is a difference-in-level stereo. But as the off-axis attenuation of a typical cardioid microphone is only around 6dB at 90 degrees, the channel separation is limited, and wide stereo images are not possible with this recording method. Therefore, XY stereo is often used where high mono-compatibility is needed - for example, in broadcasting situations where many listeners still receive the audio on mono equipment. Since the sound-sources are mainly picked up off-axis when using the XY stereo setup, high demands are placed on the off-axis response of the microphones used.

Zeppelin

A special type of microphone shock mount and wind screen assembly. It essentially consists of a sort of skeleton/shock mount surrounding a microphone over which some type of foam or muff type material is placed. The purpose is largely the same as a conventional wind screen only these can do an even better job of isolating the mic from the elements while also providing a more natural sound. Typically these are used with shotgun microphones, partly because these mics then to be extremely sensitive to mechanical (handling) noise as well as wind. Furthermore, shotguns are often used in applications where one is already trying to capture a signal that's difficult to get so any extra noise is a real problem. The name comes from the old dirigible as the appearance (and in some respects construction) is similar. They are also referred to as blimps for similar reasons.

Zoom Microphone

A type of microphone system consisting of three cardioid microphone elements and a special phase correction equalization circuit. By varying the position of a control knob, the microphone outputs are combined in such a way that the directivity of the array changes from omnidirectional through cardioid to super-cardioid. These are sometimes used in film (or video) making because the control can be synchronized with the control of a zoom lens on a camera so that the auditory perspective changes with the visual perspective.

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