Sensitive Test of Speech Communication Quality

Abstract

Small differences in the quality of various speech samples, all highly intelligible according to articulation tests, were reliably discriminated by a test which determined how easily the speech samples could be heard against a background of interfering speech. The communication quality of a degraded speech was measured by the difference, Q = T − T0, where T and T0 were the intelligibility thresholds for the degraded and high-quality reference speech, respectively. An intelligibility threshold was defined as the value of the signal-to-interference intensity ratio, where the signal speech was 50% intelligible in the presence of interfering speech. Q measures and subjective quality ratings were obtained for speech degraded by low- and high-pass filtering, additive noise, and transmission over a telephone line. The Q measures successfully discriminated differences in speech quality, and they were also monotonically related to the ratings, thereby validating the test for speech quality evaluation. Articulation scores and ratings were not monotonically related, a finding which calls into question the validity of articulation tests for the evaluation of high-quality speech samples.