Impact of phase distortion and phase-insensitive speech enhancement on speech quality perceived by hearing-impaired listeners

Phase is important for speech since it contributes to the quality and intelligibility during speech perception. Many speech enhancement algorithms lack the ability to predict phase for speech reconstruction and apply the noisy phase instead. In this study, we investigated the influence of phase distortion on the speech-quality ratings of both normal-hearing (NH) and hearing-impaired (HI) listeners by applying different degrees of random phase on speech. In one set of conditions, the speech was embedded in babble noise at 4 different signal-to-noise ratios (SNRs) from -5 to 10 dB, while in another set of conditions, the SNR was fixed at 10 dB and the speech and noise mixture was presented in simulated rooms with reverberation times ranged from 100 to 1000 ms. The speech level was kept at 65 dB SPL for NH listeners; while amplification was applied to ensure the audibility for HI listeners. Ideal ratio mask (IRM) was used for speech enhancement. Speech-quality ratings were collected following the MUSHRA procedure and compared to two objective evaluation metrics (i.e., PESQ and HASQI). Results suggest that phase distortion has negative impact on speech quality for both NH and HI listeners and this effect becomes dominant when speech enhancement was applied.