PlanetZ forums - scopeusers.com

well, this was intended as response to MusicManiac's question, but checking gave almost bizarre results.
So it ended on it's own ...

hear yourself in the attached file with 2 sections:
Scope's analog IO (set to full gain of 24dB) recorded with just an open cable dangling and then rapidly moving the mixer window in Scope.
Next section is the same, but with an Alesis iodock just plugged into the same cable.
The dock is without ANY other connection, not even PSU and as such turned off (!)
In the middle of each section there's a part normalized to -24 dB.

There's no 'movement' noticable with the open cable, but well pronounced with the line-in device.
And NO, switching it on doesn't change anything, except it picks up more noise.
so it's just a plain stupid RF antenna thingy, or wtf ...

go figure:
the infamous graph card less than an inch beneath Scope's analog processing - dead silent...
(and THIS is a 10 year old Pulsar One)
instead the stuff is picked up 5ft away from the source by an obscure circuitry
(of course I also switched off the monitor while dragging - no difference)

cheers, Tom

Hi Tom,

So the analogue I/O might be picking up all the EMI from the mains cables.
I wonder if it happens with only the digital attached.

Thanks

yes, I think so...
the same would (for obvious reasons) apply to the outputs for monitoring.
I don't seem have any noise there, as I'm using an old Philips DCC to drive headphones via S/PDIF.

well, at least it's not transmission via air (can't pick up any of that with another device here), but related to the cables connected to analog IO.
And the source IS the video card. When I plug in another (video) monitor there's a short break in the noise, which then starts again, obviously the card changes it's action while sensing the connector.

The GForce 8400 GS has it's analog connector on a short 'breakout' cable, disconnecting it didn't change the situation - which makes even short distance air transmission even less likely - leaving the slot system as the only remaining path...

while all that may be quite interesting, it should be noticed that the noisefloor of the item connected is about -74 dB, jumping up a mere 10 dB to -64 when heavily dragging a window or similiar action. So it's barely noticable at all (needs cans full throttle up)
But it IS absolutely bewildering to unplug the line cable and have it drop to -86 dB, which is a very good value for an item residing inside a computer.

cheers, Tom