Realtime implementation of high-quality 32 kbps wideband LD-CELP coder

The Wideband-Audio Low-Delay CELP (LD-CELP) coder produces speech with quality as high as the CCITT 64 kb/s standard (G.722) at half the bitrate. The computational load of the encoder is almost 900% processor time of the 12.5 MIPS DSP32c. This makes a real-time implementation impractical. We investigated the Gain-Shape Vector-Quantization (GSVQ) in order to reduce the computational load of the encoder. This paper describes a real-time implementation of the LD-CELP encoder based on the AT&T SURFboard using two DSP32c operating in parallel. A computational load of 180% processor time has been achieved. The respective decoder requires 42% processor time. The implementation of a full-duplexed coding system requires three 12.5 MIPS Digital-Signal-Processors (DSPs) and has oneway coding delay of less than 1ms. The coder also performs well for non-speech wideband audio signals such as music.