Adaptive bit-allocation between the pole-zero synthesis filter and excitation in CELP

The authors propose a CELP (code excited linear prediction) coder with a novel adaptive bit allocation between the synthesis filter and excitation by changing the filter type between an all-pole filter and a pole-zero filter. The filter type and bit allocation are determined based on the minimum perceptually weighted error criterion. When an all-pole filter is selected as the synthesis filter, the input speech is coded in the same manner as a conventional CELP coder. When a pole-zero filter is selected, the zero filter´s coefficients are coded in a closed loop. Experimental results reveal that the proposed CELP coder improves segmental signal-to-noise ratio by approximately 1 dB over a conventional CELP coder at 4.3 kb/s