Coding schemes based on PWI (Prototype Waveform Interpolation)  can supply good voiced speech quality at low bit rate (4 kbit/s). PWI algorithms generate the excitation signal for the LPC filter by interpolating prototype pitch waveforms taken from the previous and the current frame. Starting from this idea we have developed one algorithm called CB-PC (Critical Band - Prototype Coding) which allows to provide excellent quality, for voiced speech segments, at 3.3 kbit/s. This result has been achieved by means of an efficient coding and quantization of the prototype waveforms based on VQ of the critical band magnitude components as well as of a novel technique for phase coding. The work has been developed in the framework of the RACE/MAVT (Mobile Audio-Visual Terminal) project.
Bibliographic reference. Festa, Michele / Sereno, Daniele (1995): "A speech coding algorithm based on prototypes interpolation with critical bands and phase coding", In EUROSPEECH-1995, 229-232.