Psychoacoustic model

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 provides little benefit to the overall compression ratio, but psychoacoustic profiling 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 MP3,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.

Psychoacoustics is based heavily on human anatomy, especially the ear's limitations in perceiving sound. Among these limitations are:

• High frequency limit
• Temporal masking
• Spectral 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.