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

[Veronica Merryfield]

> The 100 Hz (being 2x 50Hz, the power freq. in Italy)
> suggests that it is probably related to some manner of
> power supply.  However, I have no theory why we're
> getting 2x 50Hz (and I think I need one :-)).

The implication has been that the USB audio device is a cheaper device. It is therefore more likely that the device runs from the USB 5 volt line than have a separate power supply, and that 5v line is regulated and therefore less likely to have a power line ripple on it.