Suddenly picking up computer hum after spontaneous stop

I have been using Audacity with no problems for quite some time now, but today, I was recording commentary on a Let’s Play video and I noticed that the recording had suddenly stopped after around 22 and a half minutes. As far as I can tell, it did this of its own accord, and I didn’t notice any Windows sounds accompanying it (e.g. device unplugged or anything like that). FRAPS was running at the time (with “record Windows sound” active), recording gameplay from ePSXe, and that recording was not affected in any way by the event (I’m not unfamiliar with FRAPS crashing at the slightest provocation sometimes).

Since that spontaneous stop, my microphone now picks up my computer hum as a constant baseline noise on recordings. I did not change any settings or unplug the microphone between noticing the recording had stopped and starting another recording. Turning the microphone input volume down to zero obviously makes it quieter, but I’d rather expect zero input to pick up nothing at all, so that’s odd. I don’t know whether this was also the case before, as I never had cause to test it! It doesn’t seem to be the case that the microphone is generally more sensitive, as I can discern no particular difference in it picking up my voice.

I expect the microphone is the most likely suspect, but given that it was just sitting on top of my monitor as always, not being interfered with in any way, and it still seems to be working entirely normally apart from picking up the computer hum, I don’t see what could have happened to it. I tested recording with Windows Sound Recorder and that’s also getting the hum, so that would back up the microphone (rather than Audacity) being the problem. I just find it odd that, whatever happened, it caused Audacity’s recording to halt with no fanfare.

Operating system: Windows 7 x64 SP1
The problem occurred in Audacity 2.0.3, but I have now updated to 2.0.6 and am still getting the noise baseline.
The microphone is built into my webcam (Logitech HD Webcam C270), which plugs into a USB port. No previous issues with using it.

Have you tried it on another computer? That’s easiest way to troubleshoot your idea.

If it works fine on another computer, then a bit of jiggery pokery may be in order; maybe rolling back your system to a time when it worked fine (maybe some driver issues with sound card / USB mic).

Further back? House power? Shut everything down to zero. Unplug and replug the power for each device, computer and monitor a couple of times. Also any power strips and extension cords. The case of the computer and in some cases the shield of peripherals is connected to the third (ground) prong of the power cable. Lose that ground and all those wires become antennas.

No I don’t know why Audacity would halt. But this is easy to do and it’s non-destructive.


kozikowski: I probably should have been clearer in what I meant by computer hum. It’s the physical fan noise; nothing electrical. Is the power shutdown still worth a try? Also, please clarify exactly what you mean by “shut everything down to zero”. As for Audacity halting, I’m aware that it halts if the microphone is unplugged while recording. So whatever happened to the mic, I reckon Audacity interpreted it as a momentary device disconnection. For some reason.

MangoMarr: I left the webcam where it is but plugged it into a laptop. Still getting the noise. I’ve also tried putting a shielded USB cable between the webcam plug and the computer socket, but that made absolutely zero difference.

OK, that would do it. If the webcam went off-line, Audacity would halt, but the computer would pick it right up again from the laptop built-in microphone. The one with the fan noise.

There is an easy way to tell where you’re recording from. The scratch test.


No, no, it’s the same microphone. The laptop I mentioned was for the “test it with another computer” bit.

Quick summary: Webcam mic was recording fine while I commentated on the game I was recording. Audacity suddenly stopped recording for no apparent reason. I noticed this around a minute after it happened, and took a break in my game recording. I then immediately resumed Audacity recording and game recording, still with my webcam mic, the literal only difference being the fan noise being picked up. There was no change in the hardware or software being used at any point. No changes were made to any settings on anything.

That said, it looks like it’s now behaving again, so it seems a restart fixed it (I’d have tested a restart yesterday, but I was in the middle of rendering the video). However, I’d still value any insights you might have as to what could have caused it in the first place. Otherwise, I guess this is resolved.