Weird interference/buzzing when using an audio switch box

theukmoog

theukmoog

theukmoog

Associate
Joined
12 Jul 2008
Posts
1,432
I have 2 PCs at home (a desktop/work PC and a games PC) connected to a screen/keyboard/mouse with a KVM.

I used to have Creative Labs speakers on the desktop PC and a Razer USB soundbar on the games PC.

Having recently purchased some Bose speakers from MM here, which are loads better quality than the Creative Labs speakers, I purchased a RCA/Phono switchbox so that both PCs could use the speakers.
The speakers have RCA/phono inputs, so I have 3.5mm to Phone cables from the PCs and a phono-phono cable from the switchbox to the speakers.

Speaker-Setup.jpg


Everything is fine if I just play MP3 / youtube etc from either (or both) PCs - I can use the switchbox to select which PC is coming out of the speakers and it all sounds great.

The weird thing is, if I launch a game on the games PC, as soon as the game is running, I start getting terrible buzzing / interference on the speakers.

It goes away if I unplug the desktop PC from the switchbox.

I've tried 2 different audio switch boxes and they both produce the same results.

I've tried with my old Creative Labs speakers and they produce the same results, too.

It also happens the other way round - if I play a game on the desktop PC, I get the interference and it goes away if I unplug the games PC.

And it all happens whether the other PC is powered up or not.

So weird - and I'm close to just returning this switchbox and going with dual speakers again.

Any ideas?
 
What happens when you run the problematic games PC direct to the speakers without going via the switchbox and play a game?
 
Do you have anything on the motherboard line out that tries to auto detect what's been plugged in and apply a suitable value to the output for the resistance it detected?

For example, on my main rig, it has Realtek's auto detect feature, but it also tries to apply automatically different values to send out depending on how much ohms it thinks it is detecting on the line. I did something similar to your setup, but it was going the other way instead: One PC to two identical sound system setups (Just Speakers, and Sub + Speakers) and had humming/buzzing on the sub low frequencies.

If you do, try disabling it's auto detect capabilities and see if that helps.
 
It sounds more like a floating ground issue, though it's odd it only occurs when a game is launched.

Do you have onboard as well as dedicated graphics and it's when it switches to the GPU?

For these kind of noise issues I would normally put a Ground Loop Isolator in and it cures it.
 
jaybee said:
What happens when you run the problematic games PC direct to the speakers without going via the switchbox and play a game?
Click to expand...
So with just 1 PC connected directly to the speakers, everything is fine when I play games.
1 PC going through switchbox without the other PC plugged into the switchbox and everything is fine, too.
 
Meddling-Monk said:
Do you have anything on the motherboard line out that tries to auto detect what's been plugged in and apply a suitable value to the output for the resistance it detected?

For example, on my main rig, it has Realtek's auto detect feature, but it also tries to apply automatically different values to send out depending on how much ohms it thinks it is detecting on the line. I did something similar to your setup, but it was going the other way instead: One PC to two identical sound system setups (Just Speakers, and Sub + Speakers) and had humming/buzzing on the sub low frequencies.

If you do, try disabling it's auto detect capabilities and see if that helps.
Click to expand...
No idea :(

Work/desktop PC is a GIGABYTE Z370 AORUS Gaming 7 Intel Z370 (Socket 1151) motherboard - taking sound from the headphone 3.5mm socket on the back of the motherboard.

Games PC is a ASUS TUF GAMING B650M-PLUS WIFI AMD Ryzen AM5 Micro-ATX motherboard - again, taking sound from the 3.5mm socket on the motherboard into the RCA jacks on the switch or speakers.

Are you talking about something in the BIOS or in Windows itself?
 
Whoop said:
It sounds more like a floating ground issue, though it's odd it only occurs when a game is launched.

Do you have onboard as well as dedicated graphics and it's when it switches to the GPU?

For these kind of noise issues I would normally put a Ground Loop Isolator in and it cures it.
Click to expand...
Happy to try that - they seem cheap - but would I need a Ground Loop Isolator on the output from each PC or just one after the switchbox on the cable to the speakers?
 
It's as Whoop has already said, it's some form of ground loop between those 2 PC's

The increased noise from graphics is likely RF getting onto the ground somehow.

It's worth putting both PC's on the same mains block / extension to see if that helps, but I expect it won't.

Best solution is purchase an external DAC that has 2 optical inputs, and connect each PC optically. Optical is galvanically isolated and would solve the issue.
 
Last edited:
Admetos said:
Best solution is to purchased an external DAC that has 2 optical inputs
Click to expand...
Unfortunately, only the work PC has an optical out, the games PC (Asus mobo) doesn't have optical out, so I can't try this solution :(

I've ordered a pair of ground loop isolators, so will see if that fixes it.

Thanks for the help from everyone... appreciated!
 
You must log in or register to reply here.
Back
Top Bottom