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Irritating noise coming through speakers
liamoforange
post Jul 29 2012, 20:18
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Hi,

I am getting this annoying noise through my speakers. It's like there are crickets in my computer trying to send me subliminal messages in morse code.

A sample is attached.

1. It appears once the PC powers up.
2. It appears irregardless of what sound card is used either onboard sound, or external sound card
3. It appears irregardless of what slot external sound card is installed in
4. All cables are shielded.
5. I am running a cable to an external pre-amp and then to my amp.
6. When cable from PC is disconnected the pre-amp is dead silent, when attached the noise interferes with all functions. i.e. phono
7. When PC is off, no line noise on any channel in pre-amp.
8. Sound appears when using a different source, i.e. a receiver instead of pre and power amp.
9. Have swapped out multiple cables, even had a custom shielded cable made to run from PC to pre.
10. All drivers are installed properly and up to date.

Asus P5Q-deluxe
X-Fi Platinum sound card
Win 7 x64
4gb ram

Any and all help to troubleshoot and eliminate this problem will be greatly appreciated.
Attached File(s)
Attached File  Memo1.m4a ( 99.42K ) Number of downloads: 501
 
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Fandango
post Jul 29 2012, 22:23
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That's a sympton of your typical ground loop. IBM compatible PCs were never intended to be audio equipment initially, that's why their electrical ground is connected to the audio jack's shield (screening), in fact it's like this: ground is connected to any shield of any connector, the audio jacks happen to be among them, sadly they usually don't get a special treatment by sound card or mainboard manufacturers. When there are more than two cables connected from your PC to your amp it basically creates an antenna that could pick up anything and when those radio singals are in the audible frequency range, well then they're audible. It can also happen when you have other problematic equipemt attached to your amp in addition to your PC.

The shielding of the cables is not the solution to your problem, it is the problem. But getting rid of any extra shielding won't work either, line audio connector's signalling is single ended, their shield is essential for the actual audio transmission, break that and you have no audio. Looking at the X-Fi Platinum the card's back panel which is conencted to the chassis which is connected to ground is also functioning as the screening. You can't fix it by simply cutting the loop.

You could try a radically different arrangement of your equipment, basically move the antenna away from the noise inducing source, unfortunately from the sound of the sample you've provided it's obvious the source is your PC itself.

Or you could use two DI units for each analog audio connection, creating galvanic isolation of the ground/shield antenna, breaking the loop that way. If you know how to use a soldering iron it's probably much cheaper and more elegant (no redundant functionality and parts of the DI units) to create such a device yourself. Those devices complete with four RCA jacks might even be available for sale somewhere, something such as this.

Another solution would be to use a digital audio connection between your PC and your amp instead (probably need a different pre-amp for that).

For a quick but probably inconvenient fix, that migh not even work in your case: try to disconnect your turntable from the pre-amp, not a proper solution but that worked for me once, or basically terminate all except one audio connection from your PC to your pre-amp.

This is such a common problem in sound engineering, people here probably have some more tips and tricks for you.

This post has been edited by Fandango: Jul 29 2012, 23:03
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