AUDIO ENGINEERING SUBJECTIVE EVALUATION OF HIGH QUALITY AUDIO SYSTEMS

Radio-frequency spectrum restrictions in radio broadcasting, and space limitations in other applications (such as audio storage on high cost media) demand bit-rate reduction. At the Communications Research Centre, we have been evaluating the subjective quality of audio codecs that reduce digital audio bit-rate by factors of 4 or more, depending on the application. The algorithms used to achieve such reductions are based on psychoacoustic models of hearing so that, theoretically, codecs should be able to operate transparently. With the best of these codecs, operating at their higher bit-rates, such transparency is likely to be true for average listeners. However, very subtle differences among these codecs can become magnified, for example, by operating several of these codecs in tandem, or by post-processing applied after bit-rate reduction (typical in broadcasting). Differences among the codecs may