A silence detection algorithm combined with subband coding is described. Information from each subbend is combained to determine whether speech or silence is present. This algorithm has been implemented for both two-band and five-band subband coders, and real-time system have been demonstrated using the DSP microcomputer to encode and decode speech. Results have shown that the silent intervals can be removed with almost no effect on the speech sounds.

An approach to the implementation of a discrete cosine transform (DCT) for application to coding speech is described. The approach is oriented toward single speech channel encoding. In addition, a detailed computer simulation of an adaptive transform coder is described. The purpose of the computer simulation is to determine the internal precision at various points in the implementation required to avoid subjective degradation. Specific recommmendations are made on the required internal precision in the implementation of the discrete cosine transform. A breadboard implementation of the DCT using SSI and MSI TTL logic based on the results of the computer simulation is reported.