Conversational speech quality-the dominating parameters in VoIP systems

Abstract

Delay has significant impact on the conversational quality mainly for two reasons: On the one hand the conversation between both subscribers and their interaction is more difficult. On the other hand the delay has a strong influence on the echo perception, longer transmission delay leads to an increased sensitivity in the users echo perception. It is important to evaluate the echo performance of a system in all conversational situations since typically additional artifacts like voice switching and background noise modulation may occur due to echo cancellation processes. Voice switching may be introduced at many stages in a VoIP scenario. Voice switching may lead to speech quality degradation perceived as missing syllables or missing words. Since again the effect is subjectively perceived different in single talk situations as compared to double talk situations both situations have to be taken into account. The transmission of background noise is a very critical parameter for the naturalness of a conversation. Due to clipping caused e.g. by VAD or the use of background noise reduction algorithms, background noise modulation - in combination with comfort noise injection - may degrade the perceived quality significantly. Packet loss may lead to speech quality degradation during single talk and double talk periods. The article describes objective methods which allow the assessment of various speech quality parameters relevant for the conversational quality.