onboard audio + mixer trouble

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raboof
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onboard audio + mixer trouble

Post by raboof »

I've got a setup with a pair of (low-end) studio monitors, a desktop and occasionally a laptop.

Disconnecting/reconnecting the monitors when switching between laptop and desktop is a hassle, and I might want to use both machines simultaneously, so I got a mini mixer.

The laptop soundcard is your typicial crappy onboard one (intel ich6 ac'97), but when connected to the monitors directly (from the headphone output), it happened to be sufficient for my purposes.

When connected to the mini mixer, however, there's terrible high-pitched noise. Interestingly, it seems to go away when I disconnect the power (switching to battery), or when playing an MP3 file (even when the output is muted).

What causes this? Is there anything I can do to prevent this?

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simta
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Re: onboard audio + mixer trouble

Post by simta »

its being cause by the electrical current running through, that's why it stops when you unplug the power cable.

you can get a dedicated little unit that deals with the problem, a friend uses one, not sure of make/model, will ask him and reply back.
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raboof
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Re: onboard audio + mixer trouble

Post by raboof »

simta wrote:you can get a dedicated little unit that deals with the problem, a friend uses one, not sure of make/model, will ask him and reply back.
That'd be cool!

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raboof
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Re: onboard audio + mixer trouble

Post by raboof »

I wonder if an 'audio line isolator transformer' would help here - sounds similar, but docs I've been reading suggest ground loops cause low-pitched noise (50hz) rather than high-pitched.

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Re: onboard audio + mixer trouble

Post by DioXide »

It's not a ground loop, it's switching noise from the power supply...

This is a weird situation.

Facts that fit the theory:

-It's high-pitched

-It goes away when you unplug the power supply (because batteries don't need much voltage regulation, which is where the switching action is)

-It goes away when you mute the output (which suggests that the component being affected by the noise is before the output stage)

Facts that don't fit the theory and I can't explain:

-It doesn't happen when playing an mp3 (it should be constant)

-It doesn't happen when you connect the monitors directly (this makes no sense)

--

I don't know how to solve it, sorry... Some parts of either your motherboard or the mixer or the power supply (of either) are lacking bypass capacitors/smoothing filters, but no idea which

If your mixer is USB-powered, then the noise could be on the USB power line, which would explain why it doesn't happen with the monitors
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raboof
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Re: onboard audio + mixer trouble

Post by raboof »

DioXide wrote:It doesn't happen when playing an mp3 (it should be constant)
I could imagine some component doesn't get enabled until there's actual sound to play - but that's just guessing.
It doesn't happen when you connect the monitors directly (this makes no sense)
Thought so, too! :).
If your mixer is USB-powered, then the noise could be on the USB power line, which would explain why it doesn't happen with the monitors
Nope.

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Re: onboard audio + mixer trouble

Post by roaldz »

Try taping your ground contact on the mains plug of your laptop, so it doesnt make contact to the common ground of the mains socket. It solved the problem for me. You can also try to use digital audio output from your laptop, because its an analog generated signal. You can also try to use a DI box (maybe a stereo one). These solve soo much problems:)

Roald

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Re: onboard audio + mixer trouble

Post by spm_gl »

Always check your cabling first. Try switching cables out, try re-routing them, perhaps your cable is picking up interference from a nearby power supply. Then check your levels. Are you applying too much gain on a very low signal? Then check the mixer with a different source. Then try plugging it into a different power socket. Oh, and of course make sure you're using the analog output (should be obvious).
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DioXide
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Re: onboard audio + mixer trouble

Post by DioXide »

I was just thinking, what if it's the power supply of the mixer itself feeding noise back into the power lines and then the laptop's supply not filtering it out?... That'd be the funniest thing ever, but I've seen the first part happening and the second doesn't sound too unrealistic :D

Try connecting your monitors directly to the laptop, but with the mixer plugged in and working (connected to the PC and in the same power socket as the laptop)

If you hear the noise that way, try unplugging the mixer... If it goes away, bingo. If not, try turning off the PC, which might be doing the same.

If you don't hear the noise, I quit.

I've never seen cable-to-cable interference on anything other than the cheapest consumer cables (unbalanced and unshielded and running right next to power wires... I work on domotics)
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