Subtracting one audio track from another

Audacity Help Forum Windows
1

Windows XP, Aud. 2.0.3 (I can also effect this task on Win 7 using Aud. 2.0.4).

I have two tracks, and I want to subtract one (noise) from the other. How do I do this? (Note: I haven’t tried the Noise Removal feature yet, but I will.)

2

Sure. Not a problem. Import both tracks and they will appear one above the other – and most importantly, they will both play when you press the spacebar. They add up in this case. You can play one or the other with the SOLO and MUTE buttons to the left of each track.

Select the noise track by double clicking in the blue waves and Effect > Invert. That will turn over all the blue waves so where they used to go up, they go down now, etc. It’s the negative of the track that used to be there.

Koz

3

I heard a radio program today that talked about the sounds you hear if you subtract an MP3 file from the original WAV file that the MP3 was derived from. This was exactly what I was looking for.

4

Further reading … The Ghost in the MP3

5

I heard a radio program today that talked about the sounds you hear if you subtract an MP3 file from the original WAV file that the MP3 was derived from. This was exactly what I was looking for.

You can do that and listen to the sound of the difference, but note that the sound of the difference is not the same as the difference in the sound…

For example, take a file and copy and delay it by 10mS (add 10mS of silence to the beginning) then subtract it from the original. You find the sound of the difference is huge (it will be loud) and “phasey” (comb filtered). The fact that you can hear the subtracted difference proves there is truly a difference, yet of course it’s only a very-small time difference and the files actually sound exactly the same when played independently.

6

Simply subtracting the MP3 from the WAV, even reconverting the MP3 to a WAV (freezing in the losses) and subtracting via Audacity doesn’t seem to produce the “ghost” effect. I think the subtraction may have to be done at the level of the actual time series? (BTW I’m using Audacity 2.0.6 on Windows 7).

7

To get the tracks in-sync you will have to zoom-in , and use the time-shift tool …

So the there is maximum amount of destructive interference when one track is inverted.

[ slight adjustment to the level of one track can improve the amount of cancellation ]