Toll-quality 16 kb/s CELP speech coding with very low complexity

Abstract

We present a 16 kb/s CELP coder with a complexity as low as 3 MIPS. The main thrust is to reduce the complexity as much as possible while maintaining toll-quality. This low-complexity CELP (LC-CELP) coder has the following features: (1) fast LPC quantization, (2) 3-tap pitch prediction with efficient open-loop pitch search and predictor tap quantization, (3) backward-adaptive excitation gain, and (4) a trained excitation codebook with a small vector dimension and a small codebook size. Most CELP coders require one full DSP or even two DSP chips to implement in real-time. In contrast, 3 to 6 full-duplex LC-CELP coders can fit into a single DSP chip, since each takes only around 3 MIPS to implement. This coder achieved slightly higher mean opinion stores (MOS) than the CCITT 32 kb/s ADPCM. It also exhibits good performance when tandemed with itself or transcoded with other coders.