Efficient Coding and Speech Interpolation: Principles and Performance Characterization

The BPA (block priority assignment) system combines the principle of speech interpolation with waveform coding methods for the active speech signal. Coding with variable wordlength permits adapting the demand of the speech sources to the capacity of the channel. The system emphasized in this paper not only varies the bits per source according to the number of active talkers, but also assigns the number of bits to the source that needs it most based on estimates of the SNR over the block. When ADPCM and DSI are combined to give a 4:1 compression ratio over standard PCM (data rate 16 kbits/s) no distortions are audible. The influence of transmission errors and the use of various waveform coders is considered.