Originally Posted by AndrewZander
For example, what determines which data is copied to the CD and which data is not? Is this process 'smart' enough to know what data should and should not be written to the CD?
Monty over on Xiph.org (and intermittent poster at this forum) has made a nice video explaining the quantization (xBit to yBit) part of that.
If that doesn't satiate your curiosity there is a nice article on Wikipedia. Personally I find all the integral equations and talk of entropy a bit intimidating, but it is easily ignored.
The downsampling (or upsampling, essentially the same, just in reverse) is rather simple.
If we take 96kHz to 44.1kHz as an example:
The least common denominator of 96 and 44.1 is 14112. (96x147 = 44.1x320 = 14112)
First step is to multiply the 96kHz stream by 147. Imagine beads on an elastic string, pull the string to 147 times its original length and fill the equal sized spaces between the beads with empty bits, or zeros.
Second step is to apply a low pass filter at half the sampling frequency of the frequency you are sampling down to. (44.1kHz/2 = 22.05kHz)
Third step is to divide the intermediate stream by 320. If you have that long string of beads, it would be like starting at a random place and go along picking every 320th bead, and throwing away every bead in between.
That is downsampling, simplified.
Edited by limpidglitch - 2/8/14 at 5:32pm