Hi Guys.

Just purchased a Fireface UC. Latest driver, TotalMix FX 0.924, latest firmware.

I run it with an iMac Core i3 and then unsymmetrically connect Line Out 1+2 with Yamaha HS 80 monitors. So far so good, nothing to complain about when listening to music from iTunes. BUT:

When I launch Logic Pro 9 or Cubase 5.5, the noise floor over the monitors increases dramatically. Stronger in the left monitor than in the right one but definitely on both. I can only hear it when the DAW doesn't play back anything but it's fairly noticeable then.

Now here comes the tricky part:

When I change sample rate, the pitch changes. And when I increase sample buffer size from 32 to 64 and 128, that changes pitch, too. So it's probably still there at 128 and 256, just out of hearing range by then. I read somewhere that system audio is played back with a buffer size of 512, so that might explain the absence of the problem with iTunes.

Interestingly enough, I don't have any noise like that on the phones.

So, defective unit? Something to solve with symmetrical cabling (don't have any right now)? Something that will be fixed with a software update? At first I thought it was the USB carrier frequency but that's unlikely if sample buffer size changes pitch..