The Agora Labs G.722 wideband speech codec is a programming library that implements the data
compression algorithms specified in the ITU-T G.722 Recommendation.
This speech codec uses
sub-band adaptive differential pulse code modulation (ADPCM) and provides 7 kHz wideband audio
at data rates from 48 to 64 kbps. This is useful in fixed network VoIP applications where the
required bandwidth is typically not prohibitive. This speech codec offers a significant improvement
in speech quality over older narrowband speech codecs such G.711 without an excessive increase
in implementation complexity.
This speech codec splits the frequency band into two sub-bands, a higher and a lower sub-band,
and then each sub-band is encoded using ADPCM. It has three basic modes of operation corresponding
to the bit rates used for 7 kHz audio coding: 64, 56, and 48 kbps. The latter two modes
allow an auxiliary data channel of 8 and 16 kbps respectively to be provided within the
64 kbps by making use of bits from the lower sub-band.