Subjective performance of spectral excitation coding of speech at 2.4 kb/s

This paper presents a low rate speech codec (2.4 kb/s) based on a sinusoidal model applied to the excitation signal. A frame classifier in combination with 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 for all frame classes resulting in more "natural" reconstructed speech. Informal MOS testing indicates that the 2.4 kb/s SEC system achieves MOS scores close to the existing 4 kb/s standards (differences up to 0.2 on the MOS scale) and significantly better than the existing 2.4 kb/s LPC-10 standard (difference of 1.5 on the MOS scale).