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

[Ralf Mardorf]

Gabriel M. Beddingfield wrote:
>
>
> 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

Somebody ask for ground lift before, this is regarding to your thoughts. 
I was thinking about differences for ground leakage.

No, it isn't ground.