Enhancement of differentially coded speech signals by means of quantization error correction
Peter J. J. A. Wolters · 2005
A method to increase the Signal-to-Noise Ratio (SNR) of speech codecs is presented. It has been applied to Adaptive Delta Modulation (ADM) according to Jayant's algorithm. Observations indicate that bit streams resulting from these coders and quantization errors are correlated to some extend. Based on this experience a Quantization Error Correction method (QEC) has been developed that improves the SNR of the output signal. With this method the decoder output is updated with a correction signal derived from the received bit sequence. An expression for the optimal correction level is derived. Application of the method by means of computer simulation and hardware implementation gave a 5 to 6 dB increase in SNR. There is no need to transmit additional information and a normal decoder can be used together with additional circuitry.