I'm new to audio (and signal processing in general), and I've been learning about the AAC codec. I've read that it supports 1-48 synchronous channels in a single stream. My question is: what need is there for 48 channels in a single audio stream? I understand that if you have a 7.1 speaker setup you can send a separate channel to each speaker, but what is the need for 48 separate channels?
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$\begingroup$ Only 48?? en.wikipedia.org/wiki/Wave_field_synthesis $\endgroup$ – endolith Oct 23 '13 at 3:57
Since it will most likely not hurt to have the possibility for more streams, this might for one be just to future-proof the system. Nothing would be more stupid than to specify for 8 channels and suddenly 9.1-systems become the next big thing and your codec is not suitable.
Other than that I can imagine bigger scenarios with much more channels such as recording all the voices in an orchestra. But I honestly don't know whether or not AAC is of any importance there.
As I understand it, codecs are used for much more than storing files on a hard drive. They are widely used in broadcasting and other multi-stream audio/video delivery applications where you may want to send more several channels of non-interrelated content.
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$\begingroup$ Telecomms comes to mind, where you might want to process a lot of audio streams simultaneously $\endgroup$ – Paul R Oct 22 '13 at 9:01
If content is going out internationally then you can put translations in the extra channels.