Intelligibility of synthetic speech in the presence of interfering speech

Standard articulation tests are not always sensitive enough to discriminate between speech samples which are of high intelligibility. One can increase the sensitivity of such tests by presenting the test materials in noise. In this way, small differences in intelligibility can be magnified into large differences in articulation scores. We used both a more conventional articulation test and a monosyllabic adaptive speech interference test (MASIT) to evaluate the intelligibility of nine different speech-coding techniques. We found different patterns of responses for the articulation test and MASIT. These differences can be explained by the fact that different speech-coding schemes code different acoustic-phonetic properties of the speech signal. Some of these properties are more liable to masking by interfering noise than others. Our results show that, in the case of synthetic speech, differences in intelligibility are not always magnified by adding interfering noise: they may even disappear.