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. Though this might seem like it provides little benefit to the overall compression ratio, psychoacoustic profiling routinely leads to compressed music files that are 10 to 12 times smaller than the original with no discernible loss in quality.

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

• High Frequency Limits
• 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.