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I just finished setting up my 2 PC streaming setup. I've got everything working as I want, except for the audio from the streaming PC to my main PC.
In terms of sound cards, the main PC has a 5.1 speaker system connected to the main board and a second cheap PCI sound card that was meant to accept the signal from the other PC. The streaming PC has the main board sound card and nothing else. I have a spare USB sound card that I've used to test.
Connecting speaker out from streaming PC main board to the PCI sound card's line in produces humming.
Connecting the USB sound card's speaker out to the PCI sound card's line in produces humming.
Connecting speaker out from streaming PC main board to the line in on the main board of my main PC produces humming.
Connecting the USB sound card's speaker out to the line in on the main board of my main PC produces humming.
After this, I decided that it might be the cable, so I decided to try something different to possibly rule out the cable. I connected the PCI sound card's speaker out to the main board in the same PC's line in and had no noise.
I did the same thing reverse (PCI Speaker out -> Line in Main board) and had humming again.
At this point, I don't know what's really causing the problem or how to effectively solve it.
Anyone with more audio experience than I have any ideas? It is not imperative that I fix this, but I'd like to at least attempt to fix it instead of abandoning it entirely.
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I don't understand the physics, but there's something called "ground loop" that can introduce noise, I think when connecting two devices that both are connected to power outlets. There's ground loop isolators (about $10) that can suppress much of that noise.
EDIT: Apparently, that hum from a ground loop can be avoided by having both devices on the same power outlet.
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On March 18 2013 09:46 Ropid wrote:
I don't understand the physics, but there's something called "ground loop" that can introduce noise, I think when connecting two devices that both are connected to power outlets. There's ground loop isolators (about $10) that can suppress much of that noise.
I've read about this as well. I'll give it a shot for sure.
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Ground loop issue. It's one reason pro audio connections are usually balanced.
Try running the computers from the same outlet, or try different ones.
Worst comes to worst, some kind of transformer / isolator might work. I think if you can float the USB and use the USB sound card, that would be easiest.
edit: the cheap devices are not isolators; they just remove the ground plug connection, which is something of an electrical safety hazard.
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Putting them on the same outlet didn't work. I have the powered speakers and both PCs on the same outlet and am still getting the same amount of noise.
I would just use the USB sound card, but I ended up with the same noise that way.
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It could be something else. Perhaps mic boost is on and introduces the noise as the receiving PC does some kind of amplification through the mic boost setting, while the source PC already has an amp on its line out. If it's really a ground loop, creating a connection between the metal of the two PC cases would fix it, so you could use for example any random audio cable to check for that by touching the two PCs with that cable.
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On March 18 2013 11:43 Ropid wrote:
It could be something else. Perhaps mic boost is on and introduces the noise as the receiving PC does some kind of amplification through the mic boost setting, while the source PC already has an amp on its line out. If it's really a ground loop, creating a connection between the metal of the two PC cases would fix it, so you could use for example any random audio cable to check for that by touching the two PCs with that cable.
It could be something else, but I wouldn't suspect mic boost or anything like that if it's a hum.
Actually, if you record the sound, then you could run an FFT or something and see the frequencies of the hum. (download Audacity or similar audio program, open up file, select some audio, plot spectrum, and math will automagically be done for you) If there's any peak at say multiples of 60 Hz, that's pretty conclusive.
If you're trying to connect the cases together electrically, you'd want to use a thicker cable with lower impedance than the audio signal cable, so more of the ground loop current goes through that instead, which decreases the magnitude of the symptoms. I think. This doesn't really help for higher frequencies because of the cable inductance, but I think for the mains frequency that would work.
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It isn't any mic boost, etc. I have all audio enhancements turned off and I'm running from speaker out to line in. It should just be a purely line-level signal. The sampling rate and bit depth match, as well.
I'm going to try recording to determine the frequency of the hum when I get home from work. If the results conclude that it is a ground loop even with the computers sharing an outlet, what would your next step be? I'd like to do as little manipulating electrical currents as possible, since I have no expertise in that area at all.
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Northern Ireland1200 Posts
What are the actual sounds cards you have in each machine?
Just to clarify;
PC 1 = Gaming PC
PC 2 = Streaming PC
PC 1 has 5.1 surround sound card of some description. You are coming out of this with 3.5mm cable and going into PC 2 which has just onboard sound via 3.5mm connection.
As someone has stated above, the only problem with this is, that the cable is unbalanced. 3.5mm connections usually are TRS, which allow it to carry stereo signals. It is a consumer audio cable that is prone to earth loops especially cheap unshielded cable.
The cheapest possible solution is to buy a better heavy duty 3.5mm cable and it should solve the issue.
Also, it is true you want both PCs and any attached devices (monitor, speakers, printers etc) all to be on the same mains. In your room all the sockets are on the same ring main, so it should not be a problem. However if the other PC was in another room, its likely the mains is on a different ring, and this would increase the likelyhood of ground loops.
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As improbable as it sounds, it was actually just a faulty sound card.
I tried a friend's sound card in that PCI slot and the humming was completely gone. I took back the old card and got an ASUS Xonar DG and I'm having no problems.
I still have no idea why the humming was happening when using the main board's sound card, but I'm happy to have it working.
Thanks everyone for your input and help!
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Northern Ireland1200 Posts
Its all to do with electricity and ground loops. It is also more likely to have issues with an onboard sound chip than a seperate dedicated card, as it should be of better build quality and better components.
Glad you got it sorted anyway.
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EPT![[image loading]](http://i.imgur.com/xuo8BAa.jpg)
