Bass Rolloff For Dummies

[ewakko]

I've searched and read and read and read. But I still don't understand in layman's terms bass rolloff.

I've been recording our live shows with battery module (MM-EBM-1), using the line in. I believe the bass rolloff is set at the lowest? setting 16hz.

I am happy with the recordings, and after amplifing, I noticed that there is alot of lowend and barely and mids or highs. (I observed this while playing my recording in winamp and watching the levels). So I hypothesize that if I increase the bass rolloff, the mids and highs levels will increase.

So I wanted to know if I understand this correctly. Next, can someone explain the bass rolloff settings. I've read people talking about it, but I don't understand what the levels and units mean. Lastly can someone recommend a program that I can view the levels other than winamp. I use Cool Edit pro, but I could only find the decibels and spectrometer view.

Edited March 25, 2005 by ewakko

[A440]

Open your equalizer in Winamp and you'll see sliders that go up and down. Move one, and you'll see the flat line above it change.

That flat line is a frequency-response curve. Ideally, your mics should pick up and your headphones/speakers should play back every frequency as it sounded. (In reality, every mic and speaker has its own idiosyncrasies.) Using the bass roll-off is like pulling down the slider for the bass. It tapers off how much bass goes into the MD below the frequency that you choose.

Frequency, or pitch, is expressed in Hz. The higher the note, the higher the number. Every doubling of Hz is another octave. The bottom note of a piano (A two octaves below the bottom space on the bass clef) is 27.5 Hz, the next A is 55 Hz, etc.

Your ears, and your MD, and I hope your mics, pick up 20-20,000 Hz. So if you're rolling off your bass at 16.5 Hz, you're only limiting sub-sonics, the kind of notes that rumble the floor, and in essence you're probably not rolling off any bass at all. You can try rolling off at a higher frequency. Just remember that each doubling is a whole octave.

Don't go to too high a frequency, though, or you could end up sounding like the samples here:

http://www.giant-squid-audio-lab.com/gs/gs...redbattery1.htm

which have rolled off so much bass they sound like a clock radio, in my opinion.

If the bass isn't overloading your recording, you can also equalize (EQ) the playback rather than limiting the bass as you record. In the equalizer--even Winamp's little equalizer--you can lower the bass and boost the mids or highs as you please. Cool Edit probably has a far more sophisticated equalizer than the one in Winamp, and it's likely you can save your EQ'd versions of the songs.

Another thing to think about is mic placement when you record. Is the mic close to the bass amp? Is the room very bass-y? Even a small room can have lots of different kinds of acoustics in various spots. If you can, walk around and listen in various places in the room (close your eyes) and see if there's a more balanced-sounding place than where you had your mics before.

The spectrometer view should show you the frequency spectrum, from low to high. Decibels measure volume: every 10 decibels doubles the volume.

Don't worry too much about what the levels look like, but what the recording sounds like. Is it loyal to what you heard when you were there? That's the crucial thing.

[ewakko]

ohh.....

I think I understand. I play bass, so I'd rather not roll more off.

I couldn't amplify my songs as much as I'd like because the bass would start clipping. I have two gigs this weekend, and I'll play around with the equalizer before I amplify it so I can hear the vocals better without clipping the bass.

I play in small bars so it's usually very boomy and muddy. I can't ever place the mics anywhere other than the front of the stage, but at least I can catch the vocals on the stage monitors.

[kuba]

Simple bass roll-off is only capacitor in series with the mic and input, which works like a 6dB per octave low-pass. The frequency of roll-off (capacitor value) is calculated against fixed input impedance, which has to match the input impedance of your device providing you want it to work properly.

The higher freq of roll-off you use, the lower bottom end is present in the recording. It won't raise the volume of mid- and high-range.

My two cents.

Correct me if I'm wrong.

The spectrometer view should show you the frequency spectrum, from low to high. Decibels measure volume: every 10 decibels doubles the volume.

Eeh, every 3dB doubles the volume, right?

[bug80]

Eeh, every 3dB doubles the volume, right?

←

6dB

The equation for SPL in acoustics is: SPL = 10*log10(pressure^2) = 20*log10(pressure)

So, an increase of 6 dB means multiplying the pressure with 10^(6/20) = 1.995 which is approx. a factor of 2.

* EDIT * The equation above holds if you're talking about pressure, of course. But this is the quantity used the most. The pressure is what is stored in a PCM wave file, for instance.

Edited March 26, 2005 by bug80

[kuba]

6dB

The equation for SPL in acoustics is: SPL = 10*log10(pressure^2) = 20*log10(pressure)

So, an increase of 6 dB means multiplying the pressure with 10^(6/20) = 1.995 which is approx. a factor of 2.

* EDIT * The equation above holds if you're talking about pressure, of course. But this is the quantity used the most. The pressure is what is stored in a PCM wave file, for instance.

←

Damn. Of course, you're absolutely right, I was too lazy to calculate

[mrsoul]

Isn't Bass Rolloff basically cancelled when you use the Line In on your MD?

It works basically for mic input preamps?

Any clarification is appreciated (dex, A440)...

[kuba]

Isn't Bass Rolloff basically cancelled when you use the Line In on your MD?

It works basically for mic input preamps? 

Any clarification is appreciated (dex, A440)...

←

It isn't canceled. It depends on the input impedance of the device. Line-in has higher input impedance so if the roll-off capacitor values are calculated for the MD mic-in (which is 10kOhms (?)) and you connect the roll-off to the line-in (20kOhms (?)) the roll-off requency halves. If it's calculated for the DAT mic-in (4.7kOhms) and you use it with the DAT line-in (47kOhms) the roll-off frequency is 10 times lower. Hope it's clear.

Edited March 27, 2005 by kuba

[mrsoul]

Thanks for the clarification. Canceled was probably the wrong choice of words.

[Artstar]

Isn't Bass Rolloff basically cancelled when you use the Line In on your MD?

It works basically for mic input preamps?

Input impedance does not have any effect on the actual cut-off frequency of a filter. Fact is, only the filter itself is based on an impedance that bears an effect on the frequency being fed through it.

In the case of the input impedance of the recording device, the last thing we want is for the input to function as a filter as well and so by design, the impedance does not have an effect on the unit's intended frequency response hence the reason why mismatched impedances do not affect frequency response directly.

In theory, the input of an operational amplifier has infinite impedance to prevent loading of the output device feeding it the input signal whilst the output is of zero impedance to ensure maximum power is fed out of it. So it is this operational amplifier and its resistors which contribute to its overall input impedance - not a network of caps and inductors (as caps would be used for DC blocking purposes but nothing more).

What does affect mismatched impedances, however, is the maximum power transfer which affects the entire frequency spectrum as we're now talking about an amplitude related phenomenon.

So irrespective of what the bass roll-off filter's characteristics, whatever properly designed input it is plugged into, the characteristics of the filter remain the same leaving only its overall output power transfer affected.

Edited March 28, 2005 by Artstar

[bigbeefdog]

ohh.....

I think I understand.  I play bass, so I'd rather not roll more off.

I couldn't amplify my songs as much as I'd like because the bass would start clipping.  I have two gigs this weekend, and I'll play around with the equalizer before I amplify it so I can hear the vocals better without clipping the bass.

I play in small bars so it's usually very boomy and muddy.  I can't ever place the mics anywhere other than the front of the stage, but at least I can catch the vocals on the stage monitors.

←

ewakko,

I play bass also, and thought exactly the same as you when I started doing MD recordings of our live stuff. Bass rolloff? Sacrilege! I didn't want to roll MYSELF off!

I soon found out that I *had* to. If I didn't, it was all too easy to brickwall the recording, even with phantom power to the mics and only a 4-string bass. God forbid if I did a thumb slap on either the E or A strings. I'm now using a battery box set to 12 dB/octave below 107 Hz, and the bass lines are still quite strong on the recordings.

Just remember, you're not rolling off to turn yourself down - you're rolling off to prevent the deepest notes from your bass from overpowering the recording equipment.

I put some samples over in the "Live Recording Samples" thread a while back if you're curious; that's my Lakland/Ampeg/Schroeder setup recorded through the mics and battery/rolloff box, and the deepest notes are still there in full bloom.

BBD

[bigbeefdog]

Another thing to think about is mic placement when you record. Is the mic close to the bass amp? Is the room very bass-y? Even a small room can have lots of different kinds of acoustics in various spots.  If you can, walk around and listen in various places in the room (close your eyes) and see if there's a more balanced-sounding place than where you had your mics before.

Surely good advice from an audio perspective, A440.

But frankly, when it comes to recording live gigs, you have to think more along the lines of, "where can I put this minidisc/battery box/mics equipment so that it doesn't get a beer bath from some wasted audience member......."

[bigA]

We need a filter for the guy that walk up and ask if you are taping, during the show.

[Doc Hockey]

Thanks for all the technical info, but really way too much for the novice taper. What frequencies would one want to "roll off" during a rock concert played in a club using binaural mics?

Your typical battery box with bass roll off has the following settings

16Hz

69Hz

95Hz

107Hz

160Hz

195Hz

888Hz

Any suggestions appreciated.

[bigbeefdog]

Thanks for all the technical info, but really way too much for the novice taper. What frequencies would one want to "roll off" during a rock concert played in a club using binaural mics?

Your typical battery box with bass roll off has the following settings

16Hz

69Hz

95Hz

107Hz

160Hz

195Hz

888Hz

Any suggestions appreciated.

←

Depends on a number of factors, not the least of which are the bass player's gear (a 4x10 cab will give a lot less "boom" than a 2x15, for example), the sound man's preferences, mic placement, et al.....

But as I said in another thread, I play bass in clubs (classic rock / blues band) and record our gigs... and I get the best results setting the rolloff to 95 or 107 Hz.

That is, however, with the MD setup within a few feet of my bass rig. YMMV.

[A440]

bigbeefdog is probably getting super-booming bass, which is why he's having to roll off the bottom two octaves of the music. But as he says, mic placement makes a difference.

If you're an audience member it's probably not going to be as overwhelmingly bass-y where you're listening. 16 Hz is below the 20-20,000 Hz your MD is supposed to pick up, so that may or may not make any difference at all. If you do feel there's a lot of bass in the room, I suggest 69 Hz for starters, but use your ears in the particular room. Is the mix weighted extremely strongly toward the bass? Can you feel the air being pushed by the woofer? Then go up to 95 Hz.

Ideally, do a test with the opening band and go higher if you need to.

[Doc Hockey]

bigbeefdog is probably getting super-booming bass, which is why he's having to roll off the bottom two octaves of the music. But as he says, mic placement makes a difference.

If you're an audience member it's probably not going to be as overwhelmingly bass-y where you're listening. 16 Hz is below the 20-20,000 Hz your MD is supposed to pick up, so that may or may not make any difference at all. If you do feel there's a lot of bass in the room, I suggest 69 Hz for starters, but use your ears in the particular room. Is the mix weighted extremely strongly toward the bass? Can you feel the air being pushed by the woofer? Then go up to 95 Hz.

Ideally, do a test with the opening band and go higher if you need to.

←

Thanks for the feedback. Some your suggestions are easier said than done. There is no opening band and from night to night the bass is mixed higher than others. I'll take the 69 Hz as a starting point and go from there.

[insrc]

Input impedance does not have any effect on the actual cut-off frequency of a filter. Fact is, only the filter itself is based on an impedance that bears an effect on the frequency being fed through it.

In the case of the input impedance of the recording device, the last thing we want is for the input to function as a filter as well and so by design, the impedance does not have an effect on the unit's intended frequency response hence the reason why mismatched impedances do not affect frequency response directly.

In theory, the input of an operational amplifier has infinite impedance to prevent loading of the output device feeding it the input signal whilst the output is of zero impedance to ensure maximum power is fed out of it. So it is this operational amplifier and its resistors which contribute to its overall input impedance - not a network of caps and inductors (as caps would be used for DC blocking purposes but nothing more).

What does affect mismatched impedances, however, is the maximum power transfer which affects the entire frequency spectrum as we're now talking about an amplitude related phenomenon.

So irrespective of what the bass roll-off filter's characteristics, whatever properly designed input it is plugged into, the characteristics of the filter remain the same leaving only its overall output power transfer affected.

←

So as I understand Artstar is saying that recorder's impedance should NOT have any effect on bass rolloff setting. This is contrary to all the other posts here. Could someone comment? Perhaps bass rolloff is not really a filter and this theory doesn't work here, and in fact there IS an effect?

So if impedance has an effect, then for MD line-in the bass rolloff settings should be devided by 2, right? This is based on that mic-in has 10 kOhm, and line-in has 20 kOhm. Therefore recommended here 95 or 107 Hz setting is for going mic-in, and for line-in it should be rather 160 or 195 Hz. Correct?

[jeddeth]

which mic battery / bass roll-off unit do you gouys own or recommend buying for bass heavy concert recording on a minidisc?

[The Low Volta]

I have recorded lots of concerts (bass heavy as well) with greenmachines stereo mics and battery box without bass roll-off and I prefer it that way:

- no distortion (the modded mics + b-box can easily handle the spl)

- no info missing (all you hear is in the recording and all necessary editing can be performed afterwards unlike with bass roll-off: you can never restore what you didn't record)

[A440]

Ditto to Low Volta's post. Bass is generally not a problem recording through Line-in. Just get a battery module and if the recording sounds particularly bass-heavy to you afterward, change the EQ on playback--turn down the bass, turn up the treble.

You still have a realistic recording on the disc, not one that has been diminished by bass rolloff.

Here in the USA, my basic setup is these mics:

http://www.soundprofessionals.com/cgi-bin/gold/item/SP-BMC-2

with this battery module:

http://www.microphonemadness.com/products/mmcbmminminc.htm

I like the BMC-2 because they're about as stealthy as you can get: small mics on thin wires. However, there are plenty of other microphone choices--look for 20-20,000 Hz frequency response and the best S/N (signal-to-noise) ratio you can afford.

I recently used my setup at a BIG BOOMING TECHNO SHOW (Ricardo Villalobos, Sven Vath) and I didn't even have to EQ it for a good-sounding playback.

Bass roll-off = bass ripoff.

[62v8]

Having recorded more than a few concerts ....

Method is mic -> MM Elite or Mint BBox where required -> MD or HiMD Line In ...

Here is a rough guide as to bass roll off settings (that have worked for me)

Firstly, most low end cardioid mics do not have any great sub 100Hz response so the BBox setting I use is 16Hz.

Better cardioids (I use a Rode NT4) I put straight into line in.

Can't beat that kick ass kick drum and bottom end that ends up in the recording.

Now if you are getting prominent bass ... and irrespective of whether you are in front of stage, by the desk or in front of the PA ...

I gather that you are using omni directional mics.

Change the BBox settings to 69Hz or whatever is next on the list eg 95Hz.

You will end up with a much nicer balanced sound that would only need a minor tweak if any.

Bass is still there ... just not as prominent.

Experimentation is the only forward until you find that setting that suits.

Hope that helps.

Cheers

GT

[jeddeth]

with this battery module:

http://www.microphonemadness.com/products/mmcbmminminc.htm

thanks for everyone's advice!

I got the battery module and I'm ready to record a show tonight.

2 quick questions:

1. do I still need to use the Radio shack volume attenuator? Should I? If I'm plugging the battery powered mic into the line in then its not necessary and will in fact be a hinderance, correct?

2. what setting do I put the MD at, should I just start using the auto levels and let it fly? Should I go in manually and turn the levels all the way up to 30? Or should I use manula levels and continue stting them between 12 and 17 depending on the decibles of the show, like usual?

thank you guys!

Edited January 26, 2007 by jeddeth

[greenmachine]

An attenuator will be unnecessary when recording via batt module and line-in. The level setting depends on the sensitivity of your mic and the loudness of the show, usually something between 15 (for a high sensitivity mic) 30 (for a low sens mic) should be ok. AGC is approx. the equivalent to a setting of 20, with automatic dynamic correction downwards (which will give pumping artifacts, unsuitable for music). You could try a manual setting of approx. 18-25 and start from there. If your recording will get too quiet, raise the levels the next time, or vice versa. Or, if possible at all, observe the level meter during the show. Peaks should ideally be between the 1st and 2nd mark, better somewhat lower than clipped.

Edited January 26, 2007 by greenmachine