A variable rate hybrid coder based on a synchronized harmonic excitation

A novel synchronization technique is proposed for hybrid coders employing harmonic and waveform coding. A new classification technique based on analysis by synthesis to distinguish between stationary and transitional segments is also proposed. Harmonic excitation is synchronized with the LPC residual by transmitting the location of the pitch pulse closest to the frame boundary and a phase value that represents the shape of the corresponding pitch pulse. A hybrid coder is designed to demonstrate the new techniques, which has three modes: scaled white noise excitation colored by LPC for unvoiced, ACELP for transitions, and harmonic excitation for stationary segments. Subjective listening tests show that the speech quality of the variable rate hybrid coder outperforms the quality of ITU G.723.1 coders, at maximum bit rates lower than those of G.723.1 coders.