Spectral excitation coding of speech at 2.4 kb/s

We present spectral excitation coding (SEC), a speech codec based on a sinusoidal model applied to the excitation signal. A phase dispersion algorithm allows the same model to be used for voiced as well as unvoiced and transitional sounds. The phase dispersion algorithm significantly improves the perceived quality resulting in more natural reconstructed speech. A new technique for variable dimension vector quantization called nonsquare transform vector quantization (NSTVQ) is used for quantization of the harmonic magnitudes. The SEC system at 2.45 kb/s achieved an MOS score 0.8 points higher than the 2.4 kb/s ZPC-10 standard. A preliminary 1.85 kb/s SEC system which uses zero-bit magnitude quantization is also presented. Informal listening tests indicate that the quality of the 1.85 kb/s system exceeds that of the LPC-10 standard