Low delay, middle bit rate speech coder

Abstract

A digital speech encoder and decoder have particular application to the field of 16 kbps digital communications. In the encoder, a speech signal is processed by a perceptual weighting filter, using a reconstructed speech signal, a reconstructed residual signal, and a set of filter tuning coefficients. A predictive signal, which is generated by a Short Term Predictive (STP) circuit, is subtracted from the signal outputted from the perceptual weighting filter. The difference signal is processed by a coder/decoder circuit to produce a reconstructed error signal, which is added to the predictive signal to form the reconstructed residual signal. A Linear Predictive Coding (LPC) circuit receives the reconstructed residual signal and develops the set of filter tuning coefficients. The set of filter tuning coefficients are outputted to the STP circuit, which also receives the reconstructed residual signal, and thereby generates the predictive signal. The set of filter tuning coefficients are also outputted to the perceptual weighting filter, and to a complementary inverse perceptual weighting filter. The inverse perceptual weighting filter also receives the reconstructed residual signal, in accordance with the set of filter tuning coefficients. The decoder includes identical STP, LPC, and inverse perceptual weighting filter circuits for reconstructing the received signals from the encoder.