How Cd's work

[matt_london]

<PRE>I've been doing a bit of research as to how cd's work. One bit I'm still unsure about is the gradations that are taken during a sample. Do they represent a specific frequency of sound or volume or both? Thanks</PRE>

[spaced]

see here: -

http://electronics.howstuffworks.com/cd.htm

[matt_london]

<PRE>Thanks. I checked there but it didn't say whether the gradations were releated to frequency or volume.</PRE>

[tomd]

Referring to this diagram -

They represent both at once - if you picture the sound as an analogue wave, the amplitude (described here as "Displacement") represents the volume of the sound, and the frequency is worked from the number of times the volume passes from a minimum to a maximum in a second, on this diagram, how many times the Wavelength would appear in a second. (Cycles per second, or Hertz.)

A CD is sampled at 16 bits per sample at 44.1kHz, that's 44, 100 cycles per second.
16 bits means that any single sample can
have 2^16 (about 65, 000) different values to represent the volume, and this can be represented for every one of the 44100 samples per second.
This allows audio to be sampled up to a maximum frequency of 22kHz (half the sample rate), which is convieniently the top of our hearing range - hence why 44.1kHz was chosen.

[tomd]

This is the diagram I was referring to, my browser doesn't seem to like going over links:
http://schoolnet.gov.mt/physics/imEnergy/SinWaveLabelled .jpg