Noise connecting mixer to PC

Question

I've got a Xenyx1202FX that I am trying to use to record some stuff. I connect it to the PC throughout the stereo main out into the PC (win7) line in. I am also using a UK-> EURO power adapter. Furthermore, I have also connected the PC line out into one of the stereo channels.

When trying to record with Audacity even with all the volume controls turned down, I still record this annoying buzz.

I am able to reduce the noise greatly by turning on the DC offset cancelation in the line in options, but a part of it still remains.

I wonder how this happens and how to make it disappear.

Thank you.

Answer 1

You need to get a professional sound card to get rid of that sound. It has to do with line issues with the power isolation on your DAC. The computer produces lots of variations in power level as it operates and that results in power fluctuations to the DAC. Those fluctuations result in changes in signal output which you hear as that whine. It can often be reduced by reducing what your computer is doing and if your hard drive for example is cranking away, you will actually hear variations in the sound as a result of that.

A professional grade audio interface will have a properly isolated DAC to reduce such interference and will also handle matched impedance to avoid any impedance mismatch issues. If you need a cheaper option, if your computer has bluetooth, you could use a bluetooth DAC such as the Samsung HS3000 which should at least provide better power isolation.

Answer 2

AJ offers one possible (and certainly plausible) point of trouble with your setup. I might add another.

You have a number of things interconnected. Any one of those things can introduce your buzzing sound. You could have...

• House wiring issues with improper grounding
• Poor cables suffering from EM ingress
• A ground loop occurring between anything plugged in
• Simple malfunctioning hardware (trending towards AJ's answer)

The best/only way to find out for sure, however, is to systematically eliminate one piece at a time. Eventually, you'll find out which piece (or at least between which two) is the source of the interference.

At that point, repair or replace.

Answer 3

If the mixer has a headphone (ctrl room) out, try using that instead of the mains. This is not the optimal solution, but I've had success with it in the past.

Also, make try with the effects off. Sometimes these onboard FX units will generate more noise then you would like. If this is the case but you absolutely need the mixer's effects - put a noise gate in between the mixer and the computer.