What is g.722 audio compression?

g.722 is a standard defined by the CCITT for audio compression. It is designed to provide an audio quality described as 'AM Radio' quality. This means a signal bandwidth from 50 Hz to 7 kHz and a signal resolution of 16 bits. The data rate is 64 kbit/s - which happens to be the rate at which data can be transmitted over an ISDN telephone line, or over one channel of an E1 interface. The g.722 coder can also carry digital data along with the audio data, at rates of 8 or 16 kbit/s.

The g.722 coder takes 16 bit bit data at 16 kHz (bandwidth from 50 Hz to 7 kHz) and compresses it by one fourth, to 64 kbit/s. The g.722 decoder has three 'modes':

Mode 1 decompresses the audio signal with no digital data
Mode 2 reserves the LSB of each codeword byte for digital data, leaving 7 bits for the speech: this reduces the speech rate to 56 kbit/s and accommodates digital data at 8 kbit/s
Mode 3 reserves the two LSBs of each codeword byte for digital data: this reduces the speech rate to 48 kbit/s and accommodates digital data at 16 kbit/s