Analogue to digital conversion uses the following steps:

1. Sample (snapshot) the analog signal at high frequency intervals
2. Match the signal to a specific step, identifying a chord
3. Encode the chords determined above, into an 8bit value (binary form)


Most spoken voice falls within the 300-3400Hz frequency, Nyquist theorem determines the number of samples required to quantise voice, the number of samples required is twice the highest frequency.  Nyquest determined the highest frequency for spoken voice is 4000Hz, therefore 8000 samples/sec would be required.  Encoding 8000 samples into 8bit values generates 64Kb/sec.


The G711 codec takes 8000 samples/sec and encodes them into 8bit values, streaming voice at 64kb/sec.


There are two variants of the G711 codec, a-law and u-law (u-law is used in the US, a-law is used elsewhere).    The variation is specific to the quantisation levels used.