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February 25, 2006, 6:36 pm
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using the optical digital out to my surround sound receiver. I have 5.1
surround set up in my Sound control panel.
None of the audio coming from my PC is in 5.1. The reciever only shows a
stereo signal coming into it.
Anyone know why this doesn't work? Any tests, etc. that I can try?
Re: No 5.1 surround over SPIDF?
Play back a DVD. The DVD will have AC3 encoded sound samples,
which compress a 5.1 audio image into the two available (stereo)
channels on SPDIF. The problem with SPDIF, is it is only stereo
hardware-wise, and the Dolby AC3 compression method makes it
possible to stuff more channels of info, into the two available
channels in the hardware. (When your receiver gets the stereo
feed, it recognizes that AC3 encoding is being used, and you
get 5.1 sound. The receiver should have a light that illuminates
when an AC3 stream is detected.)
AC3 comes from the DVD for free. Dolby Labs collects a licensing
fee, for any tool doing the AC3 compression process (or at least
they are supposed to be paid for the privilege). There are software
encoders, that can take a 5.1 analog signal, and convert to
digital format, suitable for sending down the SPDIF cable. The
software has a delay of 0.5 seconds to do so, and in an A/V
setting, there would be a loss of lip sync.
Thus, the zero effort answer is, you'll only get 5.1 from
a DVD. If you want more than that, there is actually a
hardware card (perhaps from Korea, don't remember) that
can make 5.1 on the fly and send it down SPDIF. Also, the
Nforce2 motherboards, that have an MCP-T Southbridge, can
do AC3 on the fly as well. Some motherboards even have
a software implemented encoder in the audio driver package,
but with the 0.5 second delay problem.