[LAU] USB audio interface and a buggy USB controller

[Alex Tinsley]

  Bill Whitlock from Jensen gave a presentation to the AES group in Los 
Angeles 3 months ago on Common Mode Rejection in Real-World 
environments, If you're interested in learning more about how to combat 
the "hum" in your audio, check out his information page, there's 
multiple application documents and an AES document (which they usually 
charge for) he has posted about dealing with noise in audio setups. Some 
of them are a lengthy read, very informative though even if you decide 
not to buy this products. Bill gives speeches regularly, if you can 
catch him at a presentation go check it out.

http://www.jensen-transformers.com/apps_wp.html

BTW: AES meetings are always free to attend.

On 9/18/2010 12:51 AM, david wrote:
> Alex Tinsley wrote:
>
>> First off any noise that you hear through your USB Audio interface is 
>> because the grounding in the audio device is using the grounding on 
>> the laptop which is most commonly data ground wired to earth ground. 
>> So you hear all computer noise through the audio output. One way to 
>> alleviate this is to lift the ground on the laptop (unplug the power 
>> adapter from the laptop or get a ground lift adapter). Noise goes 
>> away. A lot of devices suffer from this, 1394 has same issue.
>
> I only get noise on my USB soundcard when I plug it into my external 
> hub. I get no noise with it plugged directly into the laptop. I guess 
> the laptop ground is OK and the external hub's ground is junk.
>
> The hub has other devices plugged into it, I don't recall if I tried 
> using it with only the soundcard. Wouldn't be surprised if some of the 
> other USB devices on the hub (scanner, printer, MIDI interface, 
> PS/2<>USB adapter for keyboard & mouse, flash card reader) are sources 
> of noise by themselves.
>
> Thanks for the extensive info!
>