Please Tell Me What Is Pcm

[MusicBringer]

Please clarify something for me. I know what Atrac is, I use MP3s, I understand the difference between lossless and lossy. What I cannot understand is PCM. What is it?

[streaml1ne]

Please clarify something for me. I know what Atrac is, I use MP3s, I understand the difference between lossless and lossy. What I cannot understand is PCM. What is it?

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This should help: http://en.wikipedia.org/wiki/PCM

[MusicBringer]

Ta

[ROMBUSTERS]

PCM stands for pulse code modification and in easy terms is a digital representation of an analogue sound wave (cosine or sine curve). It transmits the data values in binary. It can have different characteristics (like frequency, bit depth, and bitrate) however CD standard is 44.1Khz, 16-bit, 1141Kbps

[MusicBringer]

PCM stands for pulse code modification and in easy terms is a digital representation of an analogue sound wave (cosine or sine curve). It transmits the data values in binary. It can have different characteristics (like frequency, bit depth, and bitrate) however CD standard is 44.1Khz, 16-bit, 1141Kbps

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That's better

[dex Otaku]

PCM stands for pulse code modification and in easy terms is a digital representation of an analogue sound wave (cosine or sine curve). It transmits the data values in binary. It can have different characteristics (like frequency, bit depth, and bitrate) however CD standard is 44.1Khz, 16-bit, 1141Kbps

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PCM stands for Pulse Code Modulation, and in easy terms uses binary numbers to represent the amplitude of a signal with one number, called a sample, for every pulse of a fixed clock, called the sampling rate.

i.e. an analogue to digital converter measures the ampltude of a signal and converts that measurement to a binary number once for every pulse of the sampling clock.

Amplitude is stored at a set bit-depth, and often also uses a signing bit to signify positive or negative amplitude. With CD, the bit depth is 16 bits, meaning that the amplitude is recorded as a value between 0 and 2^15 along with the sign, giving a range from -32,767 to +32,768, for a total of 2^16 values, or 65,536.

Another way of saying this is that the amplitude is sliced into 65,536 segments, and the system records which one it's currently at.

On a common graph of the analogue signal this would represent the vertical axis - amplitude, or voltage in the case of the electrical signal being converted to digital.

The sampling rate is set by a fixed clock. With CD, this pulses once every 44,100 times per second.

On a common graph of the analogue signal this would represent the horizontal axis, or time.

CD standard uses 16 bits signed, 44,100Hz sampling rate, and 2 channels, resulting in a bitrate of 1,411,200 bits per second.

A simple analogy to this would be for you to write down the temperature on a thermometre once every 5 minutes; you and the thermometre are the converter in this example, your "depth" is the number of decimal places you record to on the temperature scale you use, and your sampling rate is 5 minutes.

[zerodB]

Would an appropriate analogy be to compare audio to pictures - where the bit depth of an audio track is the number of colours available, and bit rate is analogous to the resolution of the image?

[dex Otaku]

Would an appropriate analogy be to compare audio to pictures - where the bit depth of an audio track is the number of colours available, and bit rate is analogous to the resolution of the image?

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This is a close analogy, yes, but not exactly spot-on.

You have to keep in mind that image resolution is totally independent of colour depth, whereas audio bitrate is totally dependent upon bit depth.

In terms of raw audio,

bitrate = (bit depth) * (sampling rate) * (number of channels)

and in terms of raw video,

bitrate = (colour bit depth * number of colour channels) * (framerate) * (image resolution)

Since audio is a stream [time-based] it is not directly analogous to still images, which are not.