Lossy coding exploits psychoacoustic models to make removed information inaudible

Evidence

Lossy audio coding systems: These systems make use of similar techniques to that of lossless coding but, in addition, reduce the data further by quantizing the signal to minimize the number of bits per sample. In order to achieve this with the minimum of perceived distortion, some form of psychoacoustic model is applied to control the amount of quantization that a particular part of the signal suffers. Because this type of coding removes, or loses, information from the audio signal, it is known as a “lossy coding system.” Unlike the lossless systems, these coders do not preserve the input signal; the output signal is not identical to the original input. The output signal is thus distorted but hopefully in a way that does not disturb and is inaudible to the listener. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2581

Because this type of coding removes, or loses, information from the audio signal it is known as a “lossy coding system.” Unlike the lossless systems these coders do not preserve the input signal; the output signal is not identical to the original input. The output signal is thus distorted but hopefully in a way that does not disturb and is inaudible to the listener. Examples of such systems are MPEG 1, MPEG 2, mp3, and MPEG 4, which are used on the Internet, in broadcasting and for DVDs. In the film world DTS, Sony-SDDS and Dolby AC3 are used to fit multiple channels onto standard film stock. The advantage of lossy coding is that it can compress the signal much more than a lossless system. For example, to achieve the 128 k bit data rate stereo audio that is used for mp3 coding of material on many music download sites, the audio signal has to be compressed by a factor of 11.025! — David Howard, Jamie Angus, coustics and Psychoacoustics, 2577

A psychoacoustic quantization stage, which allocates bits to the various components in the audio signal in a manner that has the minimum subjective distortion. Again, in order to do this, it has to send additional side information to the decoder, such as the number of bits allocated to each signal component. This is the only stage that removes information from the signal and is therefore the only lossy stage in the whole process. It is this stage that makes the difference between a lossy and a lossless audio coding system. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2586

Categorization

• DEFINE: Explains the core distinction between lossless and lossy audio coding via their mechanism of operation.
• XREF: Psychoacoustic masking models here directly connect to the reader’s stated interest in sound mechanics producing perceptual phenomena. — connects to: Audio compression exploits masking to discard inaudible signal parts — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 2020; Without pitch, loudness, and timbre summaries, raw partial data would overwhelm consciousness; Speech models built on optimal listening neglect constant signal degradation (+11 more)
• corroborated: 4 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2581; David Howard, Jamie Angus, coustics and Psychoacoustics, 2577; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2586