[LAD] A little quiz about audio measurements...

[Gabriel M. Beddingfield]

On Fri, 28 May 2010, Folderol wrote:
>
> Once you connect the analogue side of the the USB device to the
> installed (high quality card) you have an earth loop that traverses
> both the analogue and digital domains. You also have an +5V loop (unless
> the USB device is externally powered) This loop does not exist when the
> USB card is self testing. I still can't think exactly how, but I
> believe this is likely to be a significant part of the problem.

OK... but ground loops usually produce noise or a DC offset, 
right?  What could be causing the ground loop to oscillate?

-gabriel