Enhanced CVSD--An Embedded speech coder for 64-16 kbps

A data stream from an embedded speech coder has one or more slower data streams included. If part of the high rate data stream is discarded, the slower remaining data can be used to produce a decoded speech signal. Several embedded schemes have been developed for various rate ranges. The system described in this report covers the range from 16 to 64 kbps. At the lowest rate the coder produces a 16 kbps CVSD (continuously variable slope delta modulation) data stream compatible with standard CVSD equipment. At 32, 48 and 64 kbps the coder includes a 2, 4 or 6 bit encoding of the CVSD difference signal at an 8 kHz sample rate. At these higher rates the backbone CVSD decoder output is augmented by the 2, 4 or 6 bit difference to produce an 8 kHz sample output.