6.6 Conclusions
A parametric extension to mono or stereo audio codecs has been described that provides high-quality multi-channel capabilities at bitrates that are equal to those currently employed for stereo transmission. The subjective listening test revealed superior perceptual quality of MPEG Surround over conventional multi-channel AAC, matrixed surround, and MP3 Surround coders at an overall bit rate of 160 kbps.
Full backward compatibility is guaranteed with legacy receivers by storing parametric side information in the ancillary data part of existing compression schemes. The spatial side information is scalable between 0 and (typically) 32 kbps, although higher rates are supported for applications demanding (near) transparency.
The system described is very flexible in terms of the input and output channels; all common speaker configurations are supported. The flexibility also extends to the downmix domain. MPEG Surround features automated down mixes that can be mono, stereo, or matrixed surround compatible stereo. Even multi-channel 5.1 can be used as a down-mix for configurations with a higher number of audio channels (e.g., 7.1 or 10.2). Furthermore, support is provided for externally provided down-mixes as well. Last but not least, MPEG Surround features an enhanced matrix mode that enables up-conversion of legacy stereo material to high-quality multi-channel content.
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