Error correction scheme for vocoder pitch

A pitch error resilience scheme was developed to reduce speech distortion through narrow band channels with high bit-error-rates. Natural speech pitch changes slowly, so the pitch in the current frame can be compared with the pitch in the previous frame in the decoder. If the variation exceeds some range, the pitch in the current frame will be assumed to be erroneous and corrected. Error propagation due to erroneous pitch restoration can be avoided by delaying the restoration scheme until the next frame if the previous frame was also determined to be erroneous and was restored. Tests show, the modified restoration scheme can reduce the pitch error due to channel errors at least 10% on channels with bit-error-rates above 1%.