By exploiting this characteristic, intensity stereo coding can reduce the data rate of an audio stream with little or no perceived change in apparent quality.
More specifically, the dominance of inter-aural time differences (ITD) for sound localization by humans is only present for lower frequencies.
That leaves inter-aural amplitude differences (IAD) as the dominant location indicator for higher frequencies (the cutoff being ~2 kHz).
[1] This type of coding does not perfectly reconstruct the original audio because of the loss of information which results in the simplification of the stereo image and can produce perceptible compression artifacts.
However, for very low bit rates this type of coding usually yields a gain in perceived quality of the audio.
It is supported by many audio compression formats (including MP3, AAC, Vorbis and Opus) but not always by every encoder.
It is not limited to digital systems and can even be created with passive audio transformers or analog amplifiers.
In Opus CELT, M/S encoding is combined with an angle parameter, so that different weights can be used to maximize de-correlation.
HE-AAC also adds "correlation" information, which replicates ambience by synthesizing some difference between channels.
[6] Binaural cue coding (BCC) is the HE-AAC PS technique extended for many input channels, all downmixing to one.
MPEG Surround is similar to BCC, but allows downmixing to multiple channels, and does not seem to use ITD.
The idea is to merge a given frequency range of multiple sound channels together so that the resulting encoding will preserve the sound information of that range not as a bundle of separate channels but as one homogeneous data stream.
This will destroy the original channel separation permanently, as the information cannot be accurately reconstructed, but will greatly lessen the amount of required storage space.
When used within the MP3 compression process, joint stereo normally employs multiple techniques, and can switch between them for each MPEG frame.
After this step, any frequency area can be converted to intensity stereo by removing the corresponding part of the M/S signal's side channel.