Shaped fixed codebook search for CELP coding at low bit rates

Abstract

This paper presents a new shaped fixed codebook (FCB) search technique for code excited linear predictive (CELP) coding. The state of art CELP coding techniques operate at rates above 4.0 kbps, as it gets harder to build a good FCB contribution with a minimal bit budget. In this paper the shaped FCB search is presented to ease this problem, and achieve a better FCB contribution with a reduced bit budget. The shaped FCB search integrated to a 4 kbps CELP coder is presented and the subjective performance results are reported which show that the coder is significantly better than the IS-127 half rate coder at 4 kbps.