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

[Ralf Mardorf]

Ralf Mardorf wrote:
> 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

The switch, for totally cutting or decoupling by a capacitor.