Psychoacoustics

Psychoacoustics is the study of subjective human perception of sounds. Effectively, it is the study of psychology of acoustical perception.

Psychoacoustics in software

The psychoacoustic model provides for high quality lossy signal compression by describing which parts of a given digital audio signal can be removed (or aggressively compressed) safely -- that is, without significant losses in the quality of the sound. It explains, for example, how a sharp clap of the hands might seem painfully loud in a quiet library, but hardly noticeable after a car backfires on a busy, urban street. It might seem as if this would provide little benefit to the overall compression ratio, but psychoacoustic analysis routinely leads to compressed music files that are 10 to 12 times smaller than high quality original masters with very little discernible loss in quality. Such compression is a feature of nearly all modern audio compression formats. Some of these formats include MP3, Ogg Vorbis, Musicam (used in digital radio -- DAB, or DR --in Europe and elsewhere, based on Eureka 147), and the compression used in MiniDisc, to mention a few common audio compression standards.

Related Topics:
Lossy signal compression - MP3 - Ogg Vorbis - Musicam - DAB - DR - Eureka 147 - MiniDisc

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Psychoacoustics is based heavily on human anatomy, especially the ear's limitations in perceiving sound as outlined previously. To summarize, these limitations are:

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• High frequency limit
• Absolute threshold of hearing
• Absolute threshold of pain
• Temporal masking
• Simultaneous masking

Given that the ear will not be at peak perceptive capacity when dealing with these limitations, a compression algorithm can assign those sounds outside the range of human hearing a lower priority; by carefully shifting bits away from the unimportant components and toward the important ones, the algorithm ensures that the sounds the listener hears most clearly are of the highest quality.

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