For the CG 6565 board, the information received is already pulse code modulation (PCM) encoded.
Only 256 possible amplitude measurements can be represented with 8 bits. 256 digital values are not enough to represent the entire amplitude range of the human voice at a usable quality level. However, most of the characteristics of a voice signal that make it understandable to the human ear exist at the lower end of the amplitude range. Therefore, the values are assigned to amplitude values non-linearly, with many values available to represent various amplitudes in the low end of the range, and few values to measure the high end. This compression method is called companding.
Different companding algorithms are used in different geographic regions. A companding method called mu-law is used in the US, Canada, and Japan. Another method, called A-law, is used in the rest of the world.