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optical better than coax???

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Anonymous
July 6, 2005 5:34:32 PM

Archived from groups: rec.audio.tech (More info?)

So I've been running an optical output from a USB sound card (sound blaster
MP3+) to a Zapco DAC for a while now with great results. Today I tried to
use the coax spdif output of the on-board sound card (Via ITX board - AC97
codec) with the latest drivers into the same DAC. Oddly enough, it sounded
awful. There was a prominent high frequency distortion generated by the
midrange and highs of the music. It didn't sound like clipping distortion
or anything like that. It sounded more "digital" in nature - almost like
high frequency artifacts introduced by a poorly encoded mp3, only more
severe.

How can this be? Is this originating in the onboard sound or the DAC? I'll
be installing another DAC soon (Behringer), but it might be helpful to know
beforehand whether or not I have to keep the existing Sound Blaster USB
device installed.

More about : optical coax

Anonymous
July 6, 2005 5:34:33 PM

Archived from groups: rec.audio.tech (More info?)

"MZ" <myfirstname@mdz.junk.no-ip.junk.org> writes:
> So I've been running an optical output from a USB sound card (sound blaster
> MP3+) to a Zapco DAC for a while now with great results. Today I tried to
> use the coax spdif output of the on-board sound card (Via ITX board - AC97
> codec) with the latest drivers into the same DAC. Oddly enough, it sounded
> awful. There was a prominent high frequency distortion generated by the
> midrange and highs of the music. It didn't sound like clipping distortion
> or anything like that. It sounded more "digital" in nature - almost like
> high frequency artifacts introduced by a poorly encoded mp3, only more
> severe.
>
> How can this be? Is this originating in the onboard sound or the DAC? I'll
> be installing another DAC soon (Behringer), but it might be helpful to know
> beforehand whether or not I have to keep the existing Sound Blaster USB
> device installed.

Does seem odd, considering "bits is bits" as it were.

However, an optical medium provides no electrical connection between
the devices and hence isolates them electrically.

Coax does not provide electrical isolation.

This difference makes me wonder whether a ground loop might be
interfering with reliable digital communication over a co-ax link. Of
course a piece of on-board hardware that drives the co-ax but isn't
involved in driving the fiber might also be to blame.

Are both ends of this chain plugged into the same properly grounded
electrical circuit? Are other devices connected to other circuits
electrically connected to these systems in any way?

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | "4 lines suffice."
Anonymous
July 6, 2005 7:08:35 PM

Archived from groups: rec.audio.tech (More info?)

bmiawmb@toddh.net (Todd H.) writes:
> I may have missed it in the details...but why not use the fiber that
> was working fine?
>
> No easy way to completely rule out grounding, or to rule out a problem
> with the circuitry driving and reading the co-ax, but if these
> problems go away using fiber, seems that's the ticket....

Oh duh. You changed driver equipment. Okay.

You've got several possible things that could be the problem to narrow
down. Could be that the SPDIF output of your card isn't clean.
Maybe it's got a problem. Independently test it with other
equipment. Maybe your co-ax SPDIF cable is pooched. Maybe there is
a ground loop of some sort interfering with the digital communication
(though if you can't hear one anywhere, that seems somewhat
unlikely). Maybe the co-ax SPDIF input circuitry in your DAC is
currently or never did work but the optical was always fine. Basic
troubleshooting stuff in isolating a piece of the chain at a time from
the environment is the only way to narrow things down I'm afraid.
Sadly that's quite a bitch in an installed environment.

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | "4 lines suffice."
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Anonymous
July 6, 2005 8:20:19 PM

Archived from groups: rec.audio.tech (More info?)

> Does seem odd, considering "bits is bits" as it were.
>
> However, an optical medium provides no electrical connection between
> the devices and hence isolates them electrically.
>
> Coax does not provide electrical isolation.
>
> This difference makes me wonder whether a ground loop might be
> interfering with reliable digital communication over a co-ax link. Of
> course a piece of on-board hardware that drives the co-ax but isn't
> involved in driving the fiber might also be to blame.
>
> Are both ends of this chain plugged into the same properly grounded
> electrical circuit? Are other devices connected to other circuits
> electrically connected to these systems in any way?

I considered that as well. And to answer your question, the equipment is
installed in a car, where ground loops tend to be prevalent. The computer,
DAC, and amplifier grounds are all in the same location; there's no
"alternator whine", which is often indicative of ground loop issues (or poor
grounding in general); the computer's chassis is grounded to this point and
so are the rack rails. But I would think that if it was a grounding issue,
and there was some sort of interference introduced into the signal, then I'd
be having trouble with the digital transmission and it would "cut out" - all
or none, I guess. I would think that the problem must then lie either with
the digital to analog conversion or "after", or "before" the ADC? But is
ADC even employed in the computer? Sure, there's an analog sound output
onboard, but why would it have to go ADC->DAC to give me a spdif output?
Anonymous
July 6, 2005 9:13:25 PM

Archived from groups: rec.audio.tech (More info?)

> I may have missed it in the details...but why not use the fiber that
> was working fine?
>
> No easy way to completely rule out grounding, or to rule out a problem
> with the circuitry driving and reading the co-ax, but if these
> problems go away using fiber, seems that's the ticket....

No reason, really. The optical requires the use of an external USB device.
If the coax worked, I'd just as soon eliminate that extra device. But it
brought about a puzzling finding which I couldn't explain.
Anonymous
July 7, 2005 2:59:14 AM

Archived from groups: rec.audio.tech (More info?)

On Wed, 6 Jul 2005 13:34:32 -0400, MZ <myfirstname@mdz.junk.no-ip.junk.org> wrote:


>So I've been running an optical output from a USB sound card (sound blaster
>MP3+) to a Zapco DAC for a while now with great results. Today I tried to
>use the coax spdif output of the on-board sound card (Via ITX board - AC97
>codec) with the latest drivers into the same DAC. Oddly enough, it sounded
>awful. There was a prominent high frequency distortion generated by the
>midrange and highs of the music. It didn't sound like clipping distortion
>or anything like that. It sounded more "digital" in nature - almost like
>high frequency artifacts introduced by a poorly encoded mp3, only more
>severe.

>How can this be? Is this originating in the onboard sound or the DAC? I'll

You have broken equipment. Comparing 1230987105132085 to 1230987105132085
should be no different. Can you tell that the left one was hand typed and
the right one done with cut'n'paste? It's the same with coax vs. optical.
Anonymous
July 7, 2005 3:08:21 AM

Archived from groups: rec.audio.tech (More info?)

On Wed, 6 Jul 2005 16:26:51 -0400, "MZ"
<myfirstname@mdz.junk.no-ip.junk.org> wrote:

>It's the EPIA 800.

Which shares the same CINCH connector for digital audio and composite video
out. Could be a crosstalk related problem. Check the J11 jumper on the mobo.

Or it could be a global RFI-related problem : this mobo is only class-B
certified with silly provisos, such as using shielded everything

But IMO the real culprit is the silly resampling used by Via. Check if your
system outputs a 16/44 bitstream when playing CD's. If you've got 16/48,
you'll have to circumvent resampling, for instance by following advice given
here :
http://itx.lincomatic.com/modules.php?name=News&file=ar...


>Should I try an isolating
>transformer on the coax to see if that fixes it?

If you've got one (75/75-ohm, 5 MHz min BW), try it.

>Any other ideas?

I'm not really familiar with in-car systems.
Anonymous
July 7, 2005 3:08:22 AM

Archived from groups: rec.audio.tech (More info?)

> Which shares the same CINCH connector for digital audio and composite
video
> out. Could be a crosstalk related problem. Check the J11 jumper on the
mobo.

The jumper is currently set for dig audio and not video.

>
> Or it could be a global RFI-related problem : this mobo is only class-B
> certified with silly provisos, such as using shielded everything
>
> But IMO the real culprit is the silly resampling used by Via. Check if
your
> system outputs a 16/44 bitstream when playing CD's. If you've got 16/48,
> you'll have to circumvent resampling, for instance by following advice
given
> here :
> http://itx.lincomatic.com/modules.php?name=News&file=ar...

Looks like this is a common problem and that the problem is with the spdif.
I'd prefer to stick with winamp I guess, so it looks like my only recourse
may be to go back to optical. Anyway, here's the manual to the DAC:
http://www.zapco.com/prod/pdf/daiisl.pdf
It handles both 44 and 48 (when de-jitter is off).
Anonymous
July 7, 2005 4:37:28 AM

Archived from groups: rec.audio.tech (More info?)

On Wed, 6 Jul 2005 17:31:50 -0400, "MZ"
<myfirstname@mdz.junk.no-ip.junk.org> wrote:

>the problem is with the spdif.

The problem is with Microsoft/Intel/Creative... who have specified the
stupid AC97 set of specs.
!