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.

"MZ" 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,
--
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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?

On Wed, 6 Jul 2005 13:34:32 -0400, MZ 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.