I've recently gotten hold of a Yamaha analogue desk, and I wanted to incorporate it into my mixing setup so I don't have to stay completely in-the-box.

I've bought a few things, and had a few things from my University days, so my setup currently looks like this:

Mac - 8 output USB device (Gigaport HD) - Yamaha desk channels - stereo out - 2 input USB device (Behringer U-Control) - Mac again

Signal comes through and everything, and I can EQ it on the desk which sounds great. However, there is a constant high-pitched buzz under the whole thing. Its quiet, but its definitely there and detracts from the mix.

The buzz remains (although quieter) when I turn the desk off. The only way I've gotten rid of the buzz is to take the cables out between the desk output and the U-Control. But then I obviously don't get signal back into my computer.

I've tried going from the desk outputs to the mac directly. I've also tried going through an amp, into the U-Control. Both were still buzzy.

Can anyone help me figure out a chain that will allow me to incorporate the Yamaha desk into my mix path, without the buzzing?

Have you tried using a grounded power strip? I have buzzing issues with different wall outlets in my house. Also, I notice that the monitor of my Mac can cause buzzing issues if it's too close to some devices.
Try putting everything on the same power strip if possible.

There are some USB ports that are just noisy. When I am hooking up my drum machine to my PC via USB for example, I get added noise like you describe, once I disconnect the USB cable from the drum machine the noise disappears. In my case the noise doesn't translate on the recording, but since you're doing D/A conversion and recording the mixer fader rides then it probably will.

How about trying balanced cables if your system will take them.

In some instances the computer power supply will add noise, so try it on a battery if it is a laptop just to see if that might be the issue.
Thanks for the responses guys.

I've taken on board it might be a power issue, maybe that the USB doesn't like doing data AND power. I've switched out the U-Control for my main recording USB device that has its own power source and it seems to be fine with that. Its an ok workaround for now.

Do you know if there is a device that can give USB devices power, and make the connection to the computer for data only?
This sounds like a USB bus issue.

Try plugging your U-C into the front ports to see if it continues. If it doesn't, then you know that your bus was being taxed. At that point, it may be worth getting a PCI USB card.

As to your power question, you could get a Hub with an external power supply and use that as a bridge to see if it helps.
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Powered hub might help but then the problem with hubs is that you further dilute your USB connection by adding one more device in line.

Are we talking desktop or laptop? If desktop you could possibly get a PCI or PCIe USB card that could remove the issue.

Another thing to look at would be USB2 vs USB3, some PCs need to have USB2 support (legacy usb support) checked on their bios settings, might need to read about that on your specific machine.