[Chu]

I am currently building a system that is not going to be HTPC system. The guts of it (790GX / 780G) probably will be the guts of a HTPC based system in a year though.

When speccing out my current system, I am at the point of choosing a motherboard. The only real difference that's going to matter in HTPC land is that one features coax out, the other optical out, for audio.

I am wondering:

1. Which is the better standard, from a format/resolution standpoint?

2. Which is probably going to be better supported in a year? On high end equipment? On low end equipment?

3. Related to #1, are the converters between the two messing around with the bitstream in any way?

This information is surprisingly hard to find!

 

[L_and_P21]

go for a sound card or an external dac. that way you can try both to see which one you like better

 

[compuryan]

The general consensus from everything I've read and been told is that coaxial is superior to optical. It will give fewer errors by its construction, but many claim not to hear a difference in quality. Cables used for coax connections will also be a little more rugged than optical cables, which is a plus.

 

[obobskivich]

most motherboards that offer one, offer both (at least that I've seen) so you could always test both options

I'm gonna x2 compuryan, everything I've read is that coaxial is "better" because of less errors and less conversion (it has to go from photons to electrons on either side), however for longer distances, optical is "better" for latency


as far as support goes, both are pretty commonly supported, although cheaper equipment usually has coaxial before it has optical (because it requires less electronics to support), but with better equipment both are equally common

personally I've never noted much of a difference, although I prefer that optical lets me have much longer cables with no adverse effects (thats my only preference to optical)

and a mini hijack: L & P, you're what? the 5th utahn head-fi member? sup.
/minihijack

 

[ericj]

Quote:

Originally Posted by obobskivich /img/forum/go_quote.gif I'm gonna x2 compuryan, everything I've read is that coaxial is "better" because of less errors and less conversion (it has to go from photons to electrons on either side), however for longer distances, optical is "better" for latency

The speed of photons through high-refractive-index plastic and glass fibers and the speed of electrons through copper are both, for distances of less than a few miles, essentially 'light speed'.

And as you said, more gear is required for the optical conversion, which you'd think would introduce additional latency.

Can't say what the signal loss per meter would be. I have no idea. I've been using a ~20ft coaxial link for a couple years now, generally without issues.

One of the characteristics of the LEDs used for optical data links is that their on/off is VERY sharp, much faster than the rise and fall time on most electrical links. So there's that.

One consideration is that home theater gear is ungrounded for the express purpose of avoiding the easiest possible route for a ground loop. Chances are, your HTPC requires a grounded mains socket. And chances are, the motherboard coaxial digital isn't transformer-coupled.

This means that there is a potential for a ground loop through the coaxial digital. You can fix that by adding an isolation transformer, but that's a hassle, and a bit of DIY typically.

It's not, however, guaranteed. For years i ran a HTPC with coaxial digital on the motherboard without any ground loop issues. Don't know why - that's just how it worked out. But I've had a ground loop issue with other motherboards.

From a format/resolution standpoint, they are precisely the same.

Edit: On yeah, the one issue i have with my long coaxial link is that if a power cord runs parallel with it for too long, and i switch on or off the fluorescent lights in that room, sometimes it makes the usb sound card it's attached to reboot itself. Which is super-annoying. Transformer coupling the SPDIF at the USB end helped a lot - I don't know if the sony HT receiver it's attached to is also transformer coupled or not.

 

[milkweg]

meh...coax has less jitter but it is a negligible difference. I can't hear a difference between coax and optical so wouldn't sweat it if I was you. Use whichever is the most convenient for you.

 

[ericj]

Most of the jitter criticism about optical comes from research done in 1992.

I think optical transmitters and receivers might have evolved slightly in the last 16 years.

 

[Chu]

Thanks for the replies. I never thought about the ground loop issues at all, but I doubt the HTPC and Stereo system system are going to be on different outlets. I would be shocked if my HTPC rig ended up costing more than my headphone rig, we're not exactly talking high end here

The motherboards in question are the M3A78 Pro vs. the M3A78-T. Unless I'm misreading the specs the -T is strictly optical only

Basically it's coming down to if an extra $50 is worth the "upgrade" from coax to optical, and how important that e-SATA port is.

(M3A78 Pro
M3A78-T)

(please no AMD vs. Intel arguments, there are some very specific reasons why I am going with a Phenom that involve the programming work I do)

 

[myinitialsaredac]

Quote:

Originally Posted by compuryan /img/forum/go_quote.gif The general consensus from everything I've read and been told is that coaxial is superior to optical. It will give fewer errors by its construction, but many claim not to hear a difference in quality. Cables used for coax connections will also be a little more rugged than optical cables, which is a plus.

Problems with coaxial--> impedance mismatch (rca plugs arent native 75 ohm like the SPDIF protocol), dielectric absorption and dispersion, susceptibility to electrical frequency interference, and common ground crosstalk amongst other effects such as the skin effect.

Problems with optical--> electron to photon conversion, usually more delicate than coaxial, signal degradation over 10 feet

Benefits of coaxial-> Much sturdier, no electron to photon conversion or led implementation, good for distance

Benefits of optical-> No dielectrics, no EMI/RFI worry, no impedance mismatch reflections, no ground, no electrical effects in the cable, usually cheaper (high end optical vs high end coaxial).

Both have their ups and downs, I personally advocate trying both. Only you can decide what you like. I prefer optical, and feel it offers better sonics at a lower price, however you will find as many supporters of coaxial as you will optical.

Dave