USB Noise

[anclibertees]

Does anyone know how to fix this problem, I have a korg R3 synth and a Mackie Onyx Blackjack usb interface. The problem is that when I have the USB for the R3 connected to run the midi and the R3 outs connected to the blackjack in's, there is bad noise, this stops when I unplug the R3's USB. I thought it may be the R3's power connector getting a bad earth but it is still there when unplugged. I can record very clean without the R3 USB connected. I would use the standard midi but the Blackjack does not have midi fuctionality. It is as if there is a 2 USB connections are out of phase or something.
Does anyone have a solution to this?

[meatballfulton]

It's a ground loop due to the dual USB connections. As you noted in your other post if you blocked the USB power pin the noise went away.

There's a few possible solutions, the simplest of which may be lifting the grounds on one end only of your cabling between the synth and the interface.

Welcome to the wonderful world of computer audio

[xmlguy]

A ground-loop is a strong possibility, as Meatball suggested, however it could also be a noisy ground from the computer powersupply. The audio signal is referenced from the ground, so any noise in the audio frequency range will get transmitted through the USB ground. So another option is to try a different computer to see how that affects the noise. If the computer is a desktop/tower model with a standard kind of powersupply, sometimes you can fix the problem by upgrading it to a better quality model with a clean ground. If the computer is a laptop or has a proprietary design powersupply, you may have no way to clean up the ground. Another thing to test is to use hardware midi if you run out of options and need to buy a midi interface. Hardware midi is designed with optical isolation to eliminate a common ground between devices.

[anclibertees]

Hi thanks for your help.
I taped up power supply pin 1 on the USB plug and problem solved.

Thanks