MPEG Surround - Description

Description

MPEG Surround uses interchannel differences in level, phase and coherence equivalent to the ILD, ITD and IC parameters. The spatial image is captured by a multichannel audio signal relative to a transmitted downmix signal. These parameters are encoded in a very compact form so as to decode the parameters and the transmitted signal and to synthesize a high quality multichannel representation.

MPEG Surround encoder receives a multichannel audio signal,x1 to xN where the number of input channels is N. The most important aspect of the encoding process is that a downmix signal, xt1 and xt2, which is typically stereo, is derived from the multichannel input signal, and it is this downmix signal that is compressed for transmission over the channel rather than the multichannel signal. The encoder may be able to exploit the downmix process so as to be more advantageous. It not only creates a faithful equivalent of the multichannel signal in the mono or stereo downmix, but also creates the best possible multichannel decoding based on the downmix and encoded spatial cues as well. Alternatively, the downmix could be supplied externally (Artistic Downmix in before Diagram Block). The MPEG Surround encoding process could be ignored by the compression algorithm used for the transmitted channels (Audio Encoder and Audio Decoder in before Diagram Block). It could be any type of high-performance compression algorithms such as MPEG-1 Layer III, MPEG-4 AAC or MPEG-4 High Efficiency AAC, or it could even be PCM.