Psychophysics and Modern Digital Audio Technology

A.J.M. Houtsma, Institute for Perception Research, Eindhoven NL

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Content Summary

Psychoacoustics plays an important role in digital audio compression by exploiting "reduction of irrelevance": compressing out parts of the signal that are imperceptible to human ears. For example, the MUSICAM system passes uses a set of bandpass filters to confine quantization noise within each subband, and dynamically allocates bits to each subband as follows: If subband energy falls below the psychoacoustic "masking threshold", that part of the signal receives zero bits, otherwise it gets just enough bits to keep the quantization noise in the subband just below the psychoacoustic audible threshold. This technique is used to encode audio into a 353Kbit/sec stream that 75% of psychometric test subjects cannot distinguish from true CD quality.

Relevance to Multimedia

Given the limited effective bandwidth (relative to demands of CD-quality audio) of today's communication systems, techniques for real-time audio compression are acutely relevant if multimedia networks are to become widespread.

Rating

5 out of 5. Real engineering benefits were realized from exploiting psychoacoustic properties of human hearing, without appreciable reduction in perceived sound quality.
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