[LAU] Am I experiencing ground hum or is it something else?

[Ken Restivo]

On Sun, Nov 29, 2009 at 03:16:33PM +0000, Andrew C wrote:
> Hey all,
> 
> I'm just wondering, is the start of this short recording a ground hum
> loop? It appears to be a weird high pitched whine in there as well...
> 
> This was recorded on my yamaha psr e-403 keyboard going into my PC via
> the Phones/Output on my keyboard.. I've ruled out the fact that it's
> my PC/soundcard by trying it with an amp in a different room away from
> my  PC, but I still hear that annoying whine.
> 
> Also plugging my headphones into the phones/output port on my keyboard
> results in that annoying whine disappearing...
> 
> http://moose.linux-coders.org/what3.mp3

Yes, that is a grounding problem with your computer. Laptop, I'd guess? It sounds like the same noise I was getting in mine when I first started using it.

> 
> Could a DI box solve this problem?
> 

It didn't solve mine. Neither did changing audio interface cards.

The problem was/is that, inside the laptop itself, the mains ground is either tied directly to or inadequately coupled to the USB ground.

What solved the problem was lifing the ground pin from the A/C mains adapter. Then the noise went away. I've been using that laptop, live, and in studio, for almost 3 years now. I just remove the ground pin from the A/C.

-ken