[Fwd: 16:9 Aspect Ratio]

[Garrett Wollman]

<<On Fri, 25 Jan 2008 11:48:54 -0500, "Brian Vita" <brian_vita@cssinc.com> said:

> In the cinema world 5.1 stereo (Dolby, DTS or SDDS) is discrete in that each
> channel is recorded on the medium separately.

In the Digital TV world, and also on 5.1-channel DVDs, the audio
system used is Dolby AC3, also known as ATSC A/52.

In digital audio compression, there are several different ways to
represent multichannel sound.  The simplest way is to compress each
channel separately.  This requires the most bandwidth, because it does
not exploit redundancy between the channels.  A step down from that is
to interleave the audio information from each channel and then
compress the result; for some codecs, this is provably equivalent to
the previous case.  Stepping down again, it is possible to determine
the perceived direction of each sound in a group of samples, and
represent this as a vector (amplitude and direction); the direction of
the vector can be quantized.  There are other possibilities; I don't
know which one A/52 actually uses.

-GAWollman