Metrics for evaluating noise suppression in hearing aids

Abstract

Noise suppression in audio systems such as hearing aids typically involves modifying the speech envelope. Noisy speech segments having poor signal-to-noise ratios are attenuated while those considered to be primarily speech are left at or near full intensity. Both spectral subtraction and ideal binary mask noise suppression work on this principle. Recent work in the development of speech intelligibility and speech quality metrics indicates that the envelope fidelity, computed as the correlation coefficient between the processed noisy speech envelope and the original noise-free speech envelope, is an important factor in determining noise-suppression benefit. This result implies that the best noise suppression system is one in which the envelope of the processed noisy speech is restored to match as closely as possible that of the original noise-free speech. The potential benefits and limitations of envelope restoration for noisy speech are analyzed using the HASPI intelligibility and HASQI quality metrics, and the performance of existing noise suppression processing is compared to that of envelope restoration for both normal-hearing and hearing-impaired listeners.