Sound card crossfeed ???

On my desk I have two XP machines

  1. Desktop with a SoundMax onboard sound card
  2. laptop with a Realtek onboard soundcard
    They are plugged into the same single wall power outlet via a multi-drop, they are 3 to 4 feet apart.

Case 1
Recording interner streaming quite happily on No.1, I then record what should be a null signal on the No.2 (testing Mixer minimizing)
and I notice that ther apperas to be a non-null signal on No.2
Amplifting the No.2 recording shows that it has captured a low-level version of exactly what was playing on No.1 at the time.

Case 2
Earlier this week I was recording a null signal on No.2 and my wireless transportable phone rang, base station also lives on my desktop and is plugged into the same single power outlet. I noticed I was getting a discernible signal rather than null, subsequent amplifying of the recording showed that it had captured the phone call. My mobile desn’t seem to do this.

So my questions are:

  1. Is this EM radiation ?
  2. Is the signal being tranmitted via the power cabling?
  3. Is this unusual or does it happen a lot (and folk maybe don’t notice)?


I’m going with electronic radiation. While it is possible to get signals to go through the power line, it’s extraordinarily difficult and equipment designed to do this reliably (X10 lighting controllers) fail frequently under the best circumstances. I have a notorious front porch light that has resisted any and all attempts for twilight control and I do not have a large or complex house.

Some things mortal men were just not meant to understand.

How many people do you know with two or more computers – present company excepted? Of those, how many do audio production? Out of that subset, how many can still hear?

Change the separation. RF leakage changes a great deal in near field. If you halve the distance between the computers, the radio signal should increase many multiple times.


Boy do I feel dumb …


  1. first I tried unplagging the mains lead to the No.2 laptop - “cross-feed” still there

  2. then tried moving the laptop closer to the No.1 a bit at a time, no perceived increase in the recorded amplitude on the No.2 - but some odd paks. When I replayed the track on No.2 it was clunking sounds of the laptop being moved.

Then the penny dropped and the light finally went on - it’s recording from #2s on-board mic …

:blush: :blush: :blush: :blush: :blush: :blush: :blush: :blush: :blush: :blush: :unamused: :unamused: :unamused: :laughing: :laughing: :laughing: :laughing:

That’s certainly never happened to me…


But in retrospect I can’t figure out how the laptop’s inputdevice got switched to Mic input as this machine I always leave configured to record “Stereo Mix” form the soundcard.

I’ts possible that either the 2.0.0 installation or one of the 2.0.1 alpha’s I installed did the switch - but I never noticed, I certainly don’t recall doing it myself :confused:

If the Device Toolbar setting changed then is it possible that it picked that up from an old Audacity 1.2.x (registry) setting?

No - and I say that as it is not picking up my other 1.2.6 registry preferences settings.

It obviously did that with the very first 1.3.x I installed - but never since AFAICT