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-   -   SPDIF from Soundcard (http://www.diyaudio.com/forums/digital-source/105796-spdif-soundcard.html)

orangeshasta 24th July 2007 08:37 PM

SPDIF from Soundcard
 
Hi all,

My computer's soundcard (SB audigy 4) is super-noisy (no surprise, considering its location amidst all sorts of RFI), so I think I'm going to buy a used Dac-in-the-Box from a local shop and use that from the soundcard's SPDIF output to give my headphone amp a bit of a cleaner signal. And hope the mid-nineties DITB does as good a job at D-to-A as a modern sound card.
Anyway, my question is this: the soundcard has its SPDIF output on a 1/8" mini plug. The DITB, I believe, has an RCA input. What would be the best way to connect these two? The only adapter cables I've been able to find from 1/8" to RCA are analog cables, whose characteristic impedance is likely nowhere near the 75 ohms called for by SPDIF. Then again, RCA connectors are far from ideal for 75 ohm cable anyway (and I don't even want to think about how bad 1/8" connectors are). Would I get any real benefit by fitting an RCA connector and a 1/8" plug onto a 75 ohm coaxial cable, or would that be an insignificant improvement to the analog cable compared with the inherent flaws of the connectors?

Thanks much!

zobsky 24th July 2007 09:05 PM

Just checking here, ..is the "noise" you complain about audible, or have you tried running a loopback using, say, RightMark Audio Analyzer?

1.If you have a 5.25" breakout-bay , try turning those I/Os off (in windows sound control panel) all the stuff that goes to it (aux 2 etc .. ) That killed a lot of noise that was being injected into my audigy 2 . Use the I/O on the PCI card itself.

2. if you wait a bit, .. maybe the kx project will support the audigy 4. The Kx drivers are audibly better than the creative ones

FWIW, here are the measurements on my audigy 2 platinum. I haven't had an issue with noise using the line-out on the card.
http://img523.imageshack.us/img523/5043/rmaatestlo9.jpg

orangeshasta 24th July 2007 09:19 PM

Well, the noise definitely sounds like it's originating somewhere inside the case, rather than as a result of lousy drivers. Kinda hard to describe it...it's high frequency, and I can hear clicking as I move my mouse, move windows around, during reading/writing from/to the hard drive...it changes depending on what the computer is doing. I'm still at work right now, but I'll try suggestion #1 when I get home at some point.

Maybe it's a grounding issue with something in my computer? I'm not sure if it would be more trouble than it's worth to just try and find the source of the problem...

zobsky 24th July 2007 09:49 PM

I've experienced that issue with cheap sound cards and onboard sound, but never with the better cards, including my audigy 2.

Try disabling onboard sound, if you have it turned on.

Try moving the audigy to a different slot (perhaps the furthest away from the processor and the motherboard north/soutth bridges)

i wouldn't worry about impedances on the SPDIF connectors, ..just find a mini-plug to RCA plug . The stream is digital anyway, at that stage.

orangeshasta 24th July 2007 10:34 PM

Okay, I got home...and got some good news and some bad news. Good news is, after muting the mic-in, aux-in, line-in, and SPDI/F in, the noise is significantly less. Bad news is, it's still at a higher level than I'd like to be hearing in my headphones.

Anybody know what the usual culprits are for this sort of noise? Would somehow shielding my soundcard make a difference? I'm thinking some sort of aluminum-foil based shield, connected to the chassis but insulated from surrounding electronics by cardboard...or something of that nature. Is that a bad idea?

zobsky 24th July 2007 10:53 PM

Quote:

Originally posted by orangeshasta
Okay, I got home...and got some good news and some bad news. Good news is, after muting the mic-in, aux-in, line-in, and SPDI/F in, the noise is significantly less. Bad news is, it's still at a higher level than I'd like to be hearing in my headphones.

Anybody know what the usual culprits are for this sort of noise? Would somehow shielding my soundcard make a difference? I'm thinking some sort of aluminum-foil based shield, connected to the chassis but insulated from surrounding electronics by cardboard...or something of that nature. Is that a bad idea?


Try temporarily disconnecting the case fans (apart from CPU and power supply fan). Does your video card have a fan, and if so, is the sound card close to it? Did you try using a different PCI slot?

Do you have
1. a different sound card you could try for comparison?
2. a different PC that you could install your audigy 4 in?
3. one more thing you could try (never tried this myself). In the sound card panel , .. select recording device, .. and if the microphone is the selected recording device, try choosing a less sensitive recording device (maybe line-in ) and turn down the gain on that device.

orangeshasta 25th July 2007 12:43 PM

1. Nope
2. Nope
3. I did that, it helped a bit.

What I do find intriguing, however, is that my video card, which sits directly on top of my sound card, has a HUGE fan on it. That now seems like a likely culprit, especially considering the noise modulates with what's going on on-screen. Suppose I really should have thought of that!

When I get home tonight I'm gonna try flip-flopping stuff around, see if that helps. Thanks for the suggestions!

dangus 26th July 2007 05:03 AM

Do you have the volumes up high for wav sources on the sound card? I know I've experienced mouse noise when using headphones plugged into the speaker output, and I had to have the sound card volume set very low. If you can turn the sound card volume control up and the gain on your headphone amp down, that has to improve S/N.

Here's a link to utility that is supposed to test your system for realtime performance or something; that might help:
http://www.thesycon.de/eng/free_download.shtml

For what it's worth, I added a Toslink input to my SB Audigy 2 ZS; it's not too hard to make use of that expansion header thing on the board, which also has some digital outs on it, if you wanted Toslink out, which I'll add sooner or later. I don't know if it is as easy to do on the Audigy 4.

As for the DAC, some people have said good things about the Behringer SRC-2496 as a DAC. I'm using one as an ADC, but haven't Rightmarked it yet to see how it compares to the Audigy 2 alone. The LED bar graph meter is nice, and it does about any digital format you can ask for up to 24/96, with XLR, RCA and Toslink digital I/O. Something to consider if you're planning to digitize your analog collection and want optical isolation between the PC and the ADC.


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