This unique digitization scheme is worthy of note and is defined within CCITT standard G.722.
This algorithm is ideally suited for the broadcast industry since it provides high quality speech (0 to 7 KHz), with an optional data channel, that can be transmitted within existing 64 KBPS DS0-oriented networks (and ISDN). Because of it’s better quality, this algorithm is often used in the radio broadcast industry.
In SB-ADPCM, the frequency band is split into two sub-bands (high and low). The two bands are then encoded using ADPCM and combined into an aggregate rate of 64 KBPS. The amount of voice digital bandwidth may be 64, 56, or 48 KBPS.
Note that the latter two rates allow for an auxiliary data port of 8, or 16 KBPS, respectively.