Continuous assessment of time-varying speech quality

This paper addresses the question of whether subjects are able to assess th e perceived time varying quality of speech material continuously. A method is introduced which is characterized by a subjective continuous rating of t he perceived speech quality by moving a slider along a graphical scale. The usability of this method is illustrated with an experiment in which differ ent sequences of sentences were degraded in quality with a Modulated Noise Reference Unit. The modulation depth was varied with time and the subject's task was to assess the perceived quality. The results indicate that subjec ts can monitor speech quality variations very accurately with a delay of ap proximately 1 s. An objective speech quality measure based on an auditory p rocessing model was applied to predict the subjective speech quality result s. The speech quality measure q(C) was modified to allow for time-dependent objective measurement of the speech quality. The averaged subjective respo nse data could be modeled by the scale transformed and low-pass filtered me asure q(C)(t) with a high degree of accuracy. (C) 1999 Acoustical Society o f America. [S0001-4966(99)04810-9].