Audacity Forum

Sorry for a subject title, but I do not now technical name of it. I am not so familiar with technical stuff regarding voice recording.
What can cause that a waveform is under the central line of decibel scale?
I tried the same microphone on two different computers, and only on one of them I see this strange result.



Can somebody explain it to me?

Yes. That's DC Offset. That's a very tiny piece of the battery or computer power supply getting into your show by accident. You can't hear it, but it can cause editing nightmares.

If you use an analog microphone (not USB) then producing a digital signal for the computer depends on the sound card or external digital mixer. If there is something wrong with it, you will get a damaged digital signal -- it's not just your performance, it's your show plus that battery voltage. It can go either up or down, but you can get rid of it the same way.

Effect > Normalize > [X] Remove DC (select)

Don't let Normalize do anything else. Just remove DC.

This is what happens when you try editing two tracks, one normal and one not.

http://kozco.com/tech/audacity/pix/DCOffset.jpg

Koz

Thank you very much for the response. It clears my doubts.
I will read some technical details and familiarize with "DC Offset" term then.

Earlier analog sound systems were immune to this problem, so it was a nasty surprise when those of us who work in both found that digital would cheerfully record waves and signals that were not sound at all.

And yes, it's perfectly possible to have one computer do this and the other not. The one with this problem should not be used for sound work, because you'll have to remember to remove the negative shift "DC Offset" at each recording. Sooner or later you're going to forget and trash a show. You can't easily take this error out after you cut your show. It's too late.

Koz