HDMI audio to Toslink Spdif

rangor gubbins

rangor gubbins

rangor gubbins

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in need of a little advice here.

Question:
What is the best way to convert a video + audio HDMI signal into a video HDMI + audio SPDIF optical signal?

Background:
I have an Onkyo TX-SR506 AV receiver to power my 5.1 speakers. The AV has optical, coaxial, and HDMI inputs for audio BUT the HDMI audio input is just passthrough so does not output sound to the speakers. So I use Toslink SPDIF to input the audio into the AV receiver which works great.
Now i want to upgrade my HTPC and am looking at either a new build, or buying a 'The Little Black Box' in a few months. There's not that many mobos that have a SPDIF output these days, nor does the little black box have a optical output for audio.
So I want to be able to split an HDMI signal so that the video remains HDMI and the audio goes to SPDIF. Any ideas?
 
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hmmm, actually after a bit more research it appears that although not many motherboards have optical out on the backplate they usually have an SPDIF header internally and I just need to buy a SPDIF I/O bracket.

Don't think that will help me for the little black box though.
 
james.miller said:
They pretty much all do. What boards have you been looking at?
Click to expand...

cheers. I realised after i posted that if the boards don't have an optical out on the backplate, you can still add a separate audio bracket connected to S/PDIF internal headers. I have noticed a couple of boards that don't mention having internal spdif headers though, e.g. MSI FM2-A55M-E33 A55 Socket FM2 VGA HDMI
 
Anyone have any thoughts on what would be the better audio decoder:
my Onkyo TX-SR506 (connected to the HTPC via a Toslink cable)
a cheap(ish) motherboard (e.g. Gigabyte GA-H61M-DS2 Socket 1155 VGA 7.1 Channel Audio mATX) (connected to AV via analog RCA)
or a £30 soundcard (e.g. Asus Xonar DG 5.1 Surround Sound Card) (connected to AV via analog RCA)
?

I'm trying to work the best way to output audio from my HTPC to my 5.1 set up. Speakers are some old Missions (can't remember model off the top of my head), and a pair of fairly high quality fronts (also can't remember what they are at the moment).
 
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If you convert to analogue 5.1 in the PC then you'll have the noise from the PCs own power supply in with the signal. This might be academic. You might not be able to hear it well enough to really tell it's there, but that's besides the point. It will be there.

Maintain the signal in it's digital form for as long as possible after it leaves the PC and you'll get around this issue. i.e. decode in the amp.

You'll also benefit from features such as Night Mode which only work when the amp is decoding DD internally.
 
Sounds (no pun intended) like good advice. Thanks.
I'll look for a motherboard that has s/pdif headers on it, and buy a "SPDIF RCA Out Plate Cable Bracket" for about £10.

So you don't think the lossy compression needed for 5.1 over an optical cable is going to deteriorate the sound more than any electrical interference from the HTPC's PSU?
 
The lossy compression for DD/DTS 5.1 is already in the signal. It makes no difference whether you convert to analogue first or let the amp do the decoding. That makes no difference to the "lossy-ness" of the signal. All you can do is add noise to that signal or use DACs that do a particularly bad job.

If we presume for a moment that the DACs in the amp and soundcard are of equal quality then all that's left to differentiate is system noise. It's a fact that a PC is an electrically noisy environment for analogue signals.

In the end and at this level it could be argued that it makes no difference, or that what difference it does make is masked by other aspects of the system performance. In short, it's splitting hairs. But as I said before, that doesn't change the fact that converting to analogue in the PC adds noise to the signal. Converting outboard won't do that.

If you're talking about playing DD-True HD or DTS-MA soundtracks and down converting them then that's something different. I think with those then you have to suck it and see. A good quality 5.1/7.1 sound card might edge it over down conversion for transport via optical. The only thing to consider then that could change things is the source. You really want to try this with the native audio from BD rather than something ripped.
 
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I see, thanks for the info re the compression in DD/DTS.
I've opted for a motherboard with optical out and will use the amp's DAC for decoding.
I think this set up will keep me going for few years until I have a bigger space and more money to spend.
Cheers for the help!
 
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