Stephen D. Voran and Andrew A. Catellier

Abstract: The value or harm associated with an increase in speech coding quality depends on the type of the increase as well as the temporal location of the increase in an utterance. For example, some increases in speech coding bandwidth can be perceived as impairments. The higher quality associated with the wider bandwidth can offset the impairment, but only if the increase happens early enough in an utterance. We present a subjective speech-quality experiment that qualifies these relationships at the talk-spurt time-scale for six different combinations of AMR and SILK speech coders. If a quality increase does not include a bandwidth increase, then, on average, it is beneficial only if it occurs in the first 2.8 seconds of a talk-spurt. If a quality increase includes a bandwidth increase, then it is beneficial only if it occurs in the first 1.8 seconds of a talk-spurt.

Keywords: speech coding; speech quality; subjective testing; AMR; SILK; speech bandwidth; time-varying speech quality

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