Removing a source of audio from a recording

[rda2008]

I am recording audio and there is music in the background. Is it possible to remove the music if I have the exact music file that was being played? I want to subtract the music so I can better hear and analyze the other sounds in the recording.

Thanks.

 

[BradtheRad]

Theoretically is it possible to do this. I believe it will be a lot of work.

You'll need to align the music waveforms. You'll need to find a distinctive moment in the music, so distinctive that you can pinpoint the exact corresponding moment in the other waveform.

If they stay in time-sync, then the rest is easy. However you ought to watch carefully as to whether they get out of sync. Then you'll need to re-align the waveforms.

 

[godfreyl]

If they stay in time-sync, then the rest is easy.

Actually, the rest is extremely difficult.
The problem is that the waveform of the signal produced by the recording microphone is very different to the waveform of the signal sent to the loudspeaker playing the music. The main reasons are:
1) The loudspeaker and microphone don't have flat frequency responses.
2) Only part of the sound picked up by the microphone comes directly from the loudspeaker. Much of it reaches the microphone after reflecting off walls, floor, ceiling etc. So the microphone is picking up a mixture of the direct sound from the speaker and dozens of copies of it, each of which has been delayed a different amount. The reflected sounds will also have had their frequency responses changed in different ways, and will be attenuated by different amounts.