Morning All!
This is an interesting issue that has recently reared its ugly head
again in a slightly different form.
Originally it manifested on my Toshiba NB200 running Xubuntu 11.04
through to 12.04 (and may have been present with Puppy LInux on the same
hardware - I can't remember if that was the case now, but suspect it was*).
The setup was as follows: the NB200 was connected to my NAD PP-3 phono
amplifier via USB in order to receive a signal from my record deck,
which I would record using Audacity picking up the PP-3 as the input
source (I often rip my vinyl purchases so that I can listen to them on
my portable media player).
When the NB200 was connected to the mains via its charger a very audible
high-pitched whine would be introduced to the recording. However, by
doing the recording on battery power and the whine disappeared. At the
time I put it down to a badly shielded PSU made do with the workaround.
Fast-forward to this weekend when I got it into my head to download
Audacity on my Mac MIni running OS X 10.6.8. I hooked it up to the NAD
PP-3 and ripped a new album only to find that the issue exists with this
hardware set-up too.
Obviously the original workaround does not apply since the Mini has no
battery to fall back on, but it got me to thinking: why is this problem
manifesting at all? Surely the output from the PP3 is a digital signal
and therefore immune to electrical interference - or put another way -
where is the whine being introduced into the signal?
I guess I am stuck with the workaround for the time being, but it would
be nice to understand what is at work here, if anybody can assist.
Sean
* it definitely did not manifest on Puppy running on my old Dell work
laptop on mains power
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