Performance evaluation of band-limited LPC vocoder and band-limited RELP vocoder in adaptive feedback cancellation

Feedback oscillation is one of the major problems faced by the hearing aid users. Adaptive feedback cancellation is used to suppress the feedback by using an adaptive filter to estimate the feedback path. However, this estimate is biased due to presence of high correlation between the original input signal and the loudspeaker input signal. Bias problem produces modeling error and can result in cancellation of the desired signal. Bias reduction can be obtained by using band-limited linear predictive coding based technique (BLPC) and band-limited residual excited linear predictive coding (BRELP) based technique. The paper compares performance of band-limited linear predictive coding based vocoder and band-limited residual excited linear predictive coding based vocoder in sound quality and bias reduction. The BLPC-AFC achieves more reduction in high-frequency correlation than BRELP-AFC. However, BRELP vocoder has a better output sound quality.