Stability and performance analysis of pitch filters in speech coders

This paper analyzes the stability and performance of pitch filters in speech coding when pitch prediction is combined with formant prediction. A computationally simple stability test based on a sufficient condition is formulated for pitch synthesis filters. For typical orders of pitch filters, this sufficient test is very tight. Based on the test, a simple stabilization technique that minimizes the loss in prediction gain of the pitch predictor is employed to generate stable synthesis filters. Finally, it is observed that the quality of decoded speech improves significantly when stable synthesis filters are employed.