Pure delay effects on speech quality in telecommunications

The effect of transmission delay on speech quality in telecommunications is described, with human factors such as conversational mode and the talker's knowledge of the cause of delay taken into account. Objective quality estimation methods for delay effects are proposed, and these methods are applied in an actual communications network. A talker expects a particular response time from a partner, and delay outside this expectation time window is noticed. Taking this information into account, subjective conversational experimentation is controlled by six kinds of tasks by varying the temporal characteristics. Thus, a subjective assessment of delay effects is obtained by laboratory tests in relation to the detectability threshold, opinion rating, and conversational efficiency. Objective quality measures for each test were defined as a linear combination of temporal parameters that correspond closely to subjective qualities. The subjective quality for delay effects in commercial telephone calls can be estimated by applying the proposed objective measures to commercial calls. Long roundtrip transmission dely in the range of 500 ms gives considerable subscriber difficulties in telecommunications.