Variable-frequency synthesis: An improved harmonic coding scheme

TLDR: Harmonic Coding is synthesized in the time domain, as a superimposition of "harmonics" whose instantaneous frequency varies continuously along an interpolation curve, within each frame, so that fast pitch variations can be tracked with no difficulty.

Abstract: The Harmonic Coding concept has already shown its potential for efficiently coding speech. Previous implementations have usec a frame rate of one every 16 ms. This was mainly due to the fact that, with longer frames, even a nonstationary spectral model (of low order) cannot reproduce the zones of fast-varying pitch with the desirable quality. However, the high framing rate is a limitation, since it implies that fewer bits will be available for encoding each frame. A solution for this problem has been devised: the signal is synthesized in the time domain, as a superimposition of "harmonics" whose instantaneous frequency varies continuously along an interpolation curve, within each frame. In this way, fast pitch variations can be tracked with no difficulty. Experimental results are presented, confirming these facts. The integration of this synthesis scheme in a speech coder is discussed.