Part 1 “MPEG Surround” provides an efficient bridge between stereo and multichannel presentations in low-bitrate applications. The MPEG Surround technology supports very efficient parametric coding of multi-channel audio signals, so as to permit transmission of such signals over channels that typically support only transmission of stereo (or even mono) signals. Moreover, MPEG Surround provides complete backward compatibility with non-multichannel audio systems.
Part 2 “Spatial Audio Object Coding” represents several audio objects by first combining the object signals into a mono or stereo signal, whilst extracting parameters from the individual object signals based on knowledge of human perception of the sound stage. These parameters are coded as a low bitrate side-channel that the decoder uses to render an audio scene from the stereo or mono down-mix, such that the aspects of the output composition can be decided at the time of decoding.
Part 3 “Unified speech and audio coding”, a standard defining a single technology that codes speech, music, and speech mixed with music, and that is consistently as good as the best of the state-of-the-art speech coders such as Adaptive Multi Rate – WideBand plus (AMR-WB+) and the state-of-the-art music coders (HE-AAC V2) in the 24 kbit/s stereo to 12 kbit/s mono operating range.