Multi-frame coding of LPC parameters at 600-800 bps

Pitch-excited linear predictive coding (LPC) is widely used to code speech at 2400 b/s. The authors describe a method of coding LPC parameters which reduces the required channel bandwidth from 2400 b/s to 600-800 b/s. This method uses a split vector quantizer to code spectral parameters at 18 to 22 b/frame without excessive memory requirements. It also exploits interframe redundancy by block coding the pitch, voicing, and energy parameters, and by selectively interpolating the spectral parameters. When operating at less than 700 b/s, the system achieved as core of 90 for a three-male-speaker DRT (diagnostic rhyme test)