Modern psychoacoustic coders use sophisticated models of auditory masking to identify sets of bits for which errors in them are masked by other parts of the audio signal. In a PCM data sequence containing speech sounds, this model is inherent in each bit of the sound. The sound is transformed, via linear-predictive coding, into a representation in which it is easier to identify the various parameters of the model. At the receiving side of the transmission, a synthesis algorithm using the same model is used to reconstruct the sound from the transmitted parameters. SA and other structured-audio compression schemes compress sound by, first, exploiting another type of redundancy in signals we term structural redundancy , and second, by taking a broader and more flexible view of process redundancy.
Structural redundancy is a natural result of the way sound is created in human situations.
The same sounds, or sounds which are very similar, occur over and over again. For example, a performance of a work for solo piano consists of many piano notes. This still holds in a perceptual coding of the sound. The representation has been compressed, since we no longer transmit the perceptually redundant information about very high frequencies or exactly represent the instant directly after a very loud sound. However, with structured coding, we can exploit and remove the structural redundancy from the sound.