A 4 kbit/s renewal code excited linear prediction speech coder

This paper proposes a new 4 kbit/s speech coder based on CELP structure with 45 ms total codec delay. The coder is mainly featured by the renewal codebook of the excitation signal and the linked split-vector quantizer of line spectrum pair parameters which enable the coder to get high quality speech at low bit rate. In addition, techniques of formant enhancement in the spectral envelop and harmonic recovery in the transient region are also introduced to reduce buzzy and hoarse sounds, respectively. From the intensive listening test with intermediated response system (IRS) speech, we obtained a comparable subjective quality to 32 kbit/s ADPCM (ITU Recommendation G.726) under a nominal speech input level of -26 dB overload