On objective assessment of audio quality — A review

Abstract

Measurement of audio quality is of fundamental importance for numerous speech and audio processing applications, where the goal of quality assessment algorithms is to evaluate the quality in agreement with human's subjective feelings of audio quality. This paper includes a brief summary of the development of intrusive and non-intrusive audio quality assessment algorithms and outlines recent advancements, especially some new topics to be investigated presently. Moreover, according to the existing problems in this field, discussion of the future trend and challenges is also given. 1．IntroductionObjective assessment of audio quality brings a lot of convenience when ranking different sound processing equipments before launching them on the market as well as observing audio signals quality in on-line monitoring. The traditional way of audio quality assessment is to collect peoples' opinions on the quality in a wellcontrolled listening test, for example Recommendation ITU-R BS.1116 [1], which has limited applications for too expensive and time-consuming. Therefore, objective audio quality measurement is naturally desired. Early methods, like Signal-to-Noise-Ratio (S/N) or TotalHarmonic-Distortion (THD) are unable to emulate human's judgments especially when the methods are applied to non-linear and non-stationary modern codec [2]. As for these disadvantages, lots of researchers studied perceptual quality assessment and these works have led to several ITU standards. Among these standards, the International Telecommunications Union (ITU) standard for audio quality (BS.1387)[3], also called perceptual evaluation of audio quality (PEAQ) has been the only available standardized method for the purpose of audio quality assessment[4] while ITU-T P.862 (PESQ) [5] corresponding for the purpose of speech quality assessment. Then the research on objective audio quality assessment is based on the classic model of PEAQ through exploiting better psychoacoustic models or improving the cognitive algorithms to increase the accuracy of the evaluation. But the PEAQ has certain limitations, making it unsuitable for many applications. Hence more perfect and practical methods were proposed.According to the evaluation principle, the evaluation methods can be separated into two categories, intrusive and non-intrusive. The present evaluation approach mainly stays on the intrusive evaluation by measuring the "distortion" between the reference signal and degraded signal. Since intrusive methods need mapping the distortion values to the predicted quality metric, it requests both signals are strictly synchronized. However, in some cases, the reference signal may not be available (e.g. wireless communications, voice over IP network, communication systems for real-time monitoring, etc.), the objective quality assessment must be operated without the reference signal. This led to the development of non-intrusive objective audio quality assessment. Presently, no non-intrusive audio quality assessment algorithm has yet been standardized by the ITU althou...