jetgraphics@gmail.com wrote:
>
> Bought a Gigabyte GA-K8VM800M based on the specs claiming 5.1 audio. Of
> course, it cost an extra $20 to get the S/PDIF bracket (getting that
> was a whole 'nother tale of woe). However, when all was properly
> connected, NO 5.1 audio. The digital signal (on COAX) consisted of L &
> R signals only.
>
> Ran the set up utilities, etc, etc.
> Ran the speaker placement test.
> L, R = good.
> Sub, C, Lr, Rr = silence.
>
> Tested the receiver's digital inputs with separate digital source, ran
> THX audio test, also verified 5.1 speaker connection with test tone.
> Good receiver. Good speakers.
>
> No reply from Gigabyte, yet.
All that is missing, is a DVD movie, a software program to play the
movie, and setting it for AC3 passthru. 5.1 only works "for free", with
an AC3 encoded stream. SPDIF is inherently stereo - there are just two
channels. AC3 is a coding scheme, that compresses six channels of
information, into the space of two channels. Your receiver has the
decoder inside it, to take apart the compressed stream, and reconstitute
the original information. A light on the front of the receiver
lights up, when an AC3 stream is detected.
There are software encoders, that can take 5.1 "analog" info, and
compress the data on the fly, to make the necessary AC3. Strictly
speaking, a licensing fee needs to be paid to Dolby Labs, if
some software does that. The encoder has a delay (latency) of 0.5
seconds, which can ruin lip sync.
The Nvidia Nforce2 chipset MCP-T Southbridge, has a group of
DSP blocks, that can make AC3 on the fly as well. The latency
on Nforce2 is much better.
I believe there was also a $100 sound card from a Korean
company, whose main purpose was running SPDIF in 5.1 all
the time. Presumably that had some hardware on the card,
to make the necessary AC3.
But for free, the easiest way to test that it is working,
is to get a DVD movie, a good DVD player application, and
set it up for AC3 passthru. The necessary AC3 is already
recorded on the DVD and you've already "paid for it".
Paul