What is MPEG-2 AAC?
MPEG-2 AAC (Advanced Audio Coding) is the latest MPEG standard on perceptual audio coding. It has been standardized as ISO 13818-7 in 04/1997. It is the consequent extension of existing standards towards optimum coding efficiency. AAC is not backwards compatible towards MPEG Audio Layers-1,2,3 and thus can incorporate the latest research results without any compatibility restrictions. Due to that reason, AAC was called NBC (non backwards compatible) in early development stages.
The MPEG-2 AAC standard is a new, state of the art audio standard that provides very high audio quality at a rate of 64 kb/s/channel for multichannel operation. It provides a capability of up to 48 main audio channels, 16 low frequency effects channels, 16 overdub/multilingual channels, and 16 data streams. Up to 16 programs can be described, each consisting of any number of the audio and data elements. There are three profiles for the AAC standard, called Main Profile, Low Complexity Profile, and Scalable Sampling Rate Profile. The Main profile is intended for use when processing, and especially memory, are not at a premium. The Low Complexity profile is intended for use when cycles and memory use are constrained, and the SSR profile when a scalable decoder is required. The Main and LC profiles have been tested at 320 kb/s for 5-channel audio programmes, and both have demonstrated better quality than competing audio coding algorithms running at 640 kb/s for the 5-channel program.
