Research on objective speech quality measurements

Abstract

This is a thesis dissertation on objective speech quality measures. Two objective measures, Enhanced Modified Bark Spectral Distortion (EMBSD) and Perceptual Evaluation of Speech Quality (PESQ) were included in this study. The scope of the study covers the evaluation of EMBSD and PESQ in predicting subjective results from Mean Opinion Score (MOS) tests; an extension of PESQ to handle wideband speech; and the performance of EMBSD and PESQ on Degradation Mean Opinion Score (DMOS) tests in noise conditions. The following results are reported: (1) EMBSD can predict the quality of various conditions for a given coder, but not across coders. (2) PESQ can predict the quality of various conditions for a given coder as well as across coders. (3) While PESQ is effective in handling time shifts that occur during silence, it does not seem as effective when such shifts occur during speech. (4) A simple extension of PESQ can evaluate wideband speech as well as it evaluates narrowband speech. (5) When clean speech is used as reference, EMBSD predicts DMOS better than when noisy speech is used as reference. (6) PESQ predicts DMOS better when using noisy speech than with using clean speech as reference.