Performance analysis of DPCM codecs operating on adaptively frequency mapped 7.6 khz speech

The performance results of the adaptive DPCM speech codecs which have been used in conjunction with an Adaptive Frequency Mapping system (AFMAP) are presented. The AFMAP preprocessor operates on a wideband speech (0.3 - 7.6 KHz) and compresses the speech signal into 0.3 - 3.3 KHz telephone channel. This signal is subsequently digitized by DPCM codecs employing simple, but efficient prediction algorithms in order to reproduce wideband speech from AFMAP postprocessor output. The informal listening tests, SNRSEG measures indicate that AFMAP system in tandem with DPCM codecs significantly enhances the recovered speech compared to other bandwidth compression systems. The reproduced AFMAP speech is also preferable to 0.3 - 3.3 KHz telephone speech, digitized by the some codecs at the same transmission bit rates.