Very low complexity interpolative speech coding at 1.2 to 2.4 kbps

The recently-introduced waveform interpolation (WI) coders provide good-quality speech at low rates but may be too complex for commercial use. This paper proposes new approaches to low-complexity WI speech coding at rates of 1.2 and 2.4 kbps. The proposed coders are 4 to 5 times faster than the previously reported ones. At 2.4 kbps, the complexity is about 7.5 and 2.5 MFLOPS for the encoder and decoder, respectively. At 1.2 kbps, the complexity is about 6 and 2.3 MFLOPS for the encoder and decoder, respectively. Informal subjective evaluation shows that, at 2.4 kbps, the quality is close to that of the high-complexity coders. The quality does not significantly degrade at 1.2 kbps and it is considered sufficient for messaging applications.