Implementations
When used within the MP3 compression process, joint stereo normally employs multiple techniques and can switch between them for each MPEG frame, including simple L/R stereo. With some encoding software it is possible to force the use of joint stereo without ever using L/R stereo. Within the LAME encoder, this is known as forced joint stereo.
Ogg Vorbis stereo files can employ either LR stereo or joint stereo. When using joint stereo, both MS stereo and intensity stereo methods may be used. As opposed to MP3 where MS stereo (when used) is applied before quantization, an Ogg Vorbis encoder applies MS stereo to samples in the frequency domain after quantization, making application of MS stereo a lossless step. After this step, any frequency area can be converted to intensity stereo by removing the corresponding part of the MS signal's S part. Ogg Vorbis' floor function will take care of the required left-right panning.
Read more about this topic: Joint (audio Engineering)