On Fri, 28 May 2010 13:23:21 -0500 (CDT)
"Gabriel M. Beddingfield" <gabrbedd@email-addr-hidden> wrote:
>
>
> On Fri, 28 May 2010, Veronica Merryfield wrote:
>
> >
> >> 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.
>
> Yes, as I go back and read that A was proven by A... it
> could be the power source for either device -- and most
> likely the "cheaper" card A.
>
> -gabriel
OK, had a bit more of a think.
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.
-- Will J Godfrey http://www.musically.me.uk Say you have a poem and I have a tune. Exchange them and we can both have a poem, a tune, and a song. _______________________________________________ Linux-audio-dev mailing list Linux-audio-dev@email-addr-hidden http://lists.linuxaudio.org/listinfo/linux-audio-devReceived on Sat May 29 00:15:08 2010
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