A high quality voice coder with integrated echo canceller and voice activity detector for VSAT systems

Low bit rate speech coding research has received much attention resulting in newly developed good quality speech coders operating at as low as 4.8 kb/s. Although speech quality at around 8 kb/s is acceptable for a wide variety of applications, at 4.8 kb/s more improvements in quality are necessary to make it acceptable to the majority of applications and users. In addition to the required low bit rate with acceptable speech quality, other facilities such as integrated digital echo cancellation and voice activity detection are now becoming necessary to provide a cost effective and compact solution. The authors describe a pulsed residual excited linear prediction (PRELP) speech coder with integrated echo canceller and a voice activity detector all of which have been implemented on a single DSP32C with 32 kBytes of SRAM. The quality of coded speech has ben improved significantly by a new excitation implementation which also simplifies the encoder/decoder complexity making room for the integration of a 64-tap echo canceller together with a voice activity detector