From Audacity Manual
Invert does not usually affect the sound of the audio at all, but it can be used for audio cancellation. If Invert is applied to one track and that track is mixed with another uninverted track that has identical audio, the identical audio is cancelled out (silenced).
- Accessed by:
- There is no effect dialog containing parameters for this effect; Invert operates directly on the selected audio.
- If the inversion takes an appreciable time, a progress dialog will appear as below:
- Manually remove vocals: This will only work where the left and right channels of a stereo song both contain equal amounts of the exact same vocals, but unequal amounts of background instruments.
- Also see the similar but more configurable Vocal Remover effect.
- Find out how different the stereo channels are: Use the same steps 1 and 2 above on any stereo track. If the audio is just as loud after the steps as before, the channels are very different. If the result is silence, the track is not really stereo but dual mono, where both left and right contain completely identical audio.