A crackling sound comes out of my speakers whenever the network is used

November 18, 2005 7:50 AM

A crackling sound comes out of my speakers whenever the network is used

I have a Terratec Aureon Fun 5.1 soundcard, that has a digital (SPDIF) connection to a Samsung home cinema set. This setup has worked flawlessly for years. I recently moved and now use ethernet instead of wireless. Now, whenever the network is used, a crackling sound comes out of the speakers, regardless whether there is music playing or not.

Does anyone know what is causing this, and how I can fix it? It's driving me insane!

Oh, BTW, I'm using Ubuntu Linux, kernel 2.6.12 and ALSA.

posted by CKZ to computers & internet (9 comments total)

Are the sound card & NIC near each other? I've heard of people complaining about interference from internal components messing up their audio. Since it can happen while you're not playing any sound it seems unlikely (to me) that it's software-related (ie., it's not caused by things duelling for CPU time).

Try shielding your soundcard. I'm not actually familiar with how one might do this, but perhaps you could find some old antistatic packaging?
posted by aramaic at 8:01 AM on November 18, 2005

A more likely thing to check is if you have any Cat5 running right alongside speaker wires...

Cat5 is supposed to be shielded, as is speaker wire, but sometimes the shielding on one or both isn't so good... you may need to upgrade cables.
posted by twiggy at 8:10 AM on November 18, 2005

Since it can happen while you're not playing any sound it seems unlikely (to me) that it's software-related (ie., it's not caused by things duelling for CPU time).

Indeed, if I plug a pear of headphones directly into the soundcard, the crackling sound is gone -- does this rule out interference?

Are the sound card & NIC near each other?

No, there are three other PCI slots between them (of which only one is used, for the wireless network).
posted by CKZ at 8:15 AM on November 18, 2005

Hmm... the SPDIF-, ethernet- and speaker cables are indeed all on top of eachother behind my desk...

I'll see if I can disentangle this mess.
posted by CKZ at 8:19 AM on November 18, 2005

I can't really test things at the moment, because most of the cables are too short. However, it seems twiggy is on the right track: the only thing that has changed is the addition of the ethernetcable. The rest of the cables have always been very close to each other.

I'll try changing ethernetcables in the coming days. I'm confident it will work.
posted by CKZ at 9:00 AM on November 18, 2005

Normal Cat5 cables are unshielded; their balanced twisted signal wires are supposed to reject and cancel out interference. Unfortunately that's sometimes not enough, as you can see. If you can't separate the cables enough, they make shielded twisted pair ethernet cables that have a foil shield jacket under the insulation. They're a little hard to find, but may be an option.
posted by zsazsa at 9:17 AM on November 18, 2005

I get this, too, CKZ. If I turn up the speaker enough, I hear the mouse moving and the hard drive being accessed. Little tiny buzzy electronic sounds. I've been told that it's a grounding problem. I haven't tried ungrounding everything yet so I don't know for sure.

It's really, really annoying.
posted by redteam at 10:03 AM on November 18, 2005

yea my bad on the "cat5 is supposed to be shielded".. somehow my brain forgot that "UTP" is unshielded twisted pair...

it's probably not twisted so well if it's causing interference... :-p
posted by twiggy at 2:06 PM on November 18, 2005

Twisting works to cancel in the far-field case. If the cables are right next to each other, it's not really far-field and you can get interference. If the interference flips bits randomly in the SPDIF signal, you can get significant crackle.

So yeah, try moving them apart.
posted by polyglot at 9:50 PM on November 18, 2005