Instantaneous and Overall Judgements for Time-Varying Speech Quality: Assessments and Relationships

This study investigates the perception of time-varying speech quality in telephony. Two experiments were conducted, in which a method of continuous judgement was used in order to study instantaneous reactions of listeners facing quality fluctuations over time, and their consequences on overall perceived quality. The aim of the first experiment was to validate the method used for various quality evolutions over time. In a second experiment, the relationship between instantaneous and overall judgements was investigated. The results of the first experiment validate the method and show that subjects react with different time constants to large sudden quality degradations (about 10 seconds) or improvements (about 30 seconds). The second experiment demonstrated that the location of a quality degradation or improvement influenced subjects' overall judgements, revealing a recency effect.