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- Onboard optical SPIDF supporting surround?
March 24, 2006, 12:57 pm
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Re: Onboard optical SPIDF supporting surround?
SPDIF is typically stereo (two channel). It is a digital stream.
If a specially encoded digital stream is used, it is possible to
compress and fit 5.1 channel sound into the stereo stream.
That is called AC3 encoding, and that stream can come from a
DVD during playback. The SPDIF receiver has to have a decoder
to convert the 5.1 compressed stream, back into signals for
all the speakers.
There are some real time compressor products, like there was a
PCI sound card from Korea, that could convert 5.1 channels on
the computer continuously to AC3 SPDIF. The card was maybe $100,
but I haven't kept track of whether they are still in business
Some computer sound chips come with a software AC3 encoder, but
there is a 0.5 second delay in the encoder. I doubt you would
be very happy with that.
The Nforce2 MCP-T Southbridge has DSP capability, and had the
ability to make AC3 on the fly, with less latency than the
pure software method. I've never had a chance to experiment
with mine, as my stereo has no SPDIF.
I believe AC3 encoding requires a license from Dolby, and is
one reason there are not more hardware implementations. Even
if the license only added $0.25 to a chip's cost, I doubt it
would be included.
There is more info here: