Inversion audio filter

[sun]

A filter that inverts selected audio channels would be useful, for example to process a balanced signal from an XLR microphone.

[cehoyos]

Even if this may be clear for many developers, please explain what "audio inversion" means.

[sun]

I think (hope) the right english term is phase inversion. This means that the displacement of an audio wave is inverted.

This gives further information about balanced audio, which is commonly used:
 http://en.wikipedia.org/wiki/Balanced_audio

[Cigaes]

If I understand correctly, that means that for stereo signal, the left signal must be kept unchanged and the right signal must be multiplied by -1?

[sun]

Right. After that you merge the two signals into one mono signal which iwill be free of interferences.

[richardpl]

I think this can already be done with pan filter.

[richardpl]

See:

ffmpeg -i input -af pan="stereo:c0=c0:c1=-1*c1" -ac 1 out

[sun]

Ah, I see. Didn't know that the pan filter takes negative gain values, too. So this request is obsolete of cause, thanks for the hint!

[cehoyos]

Thank you for confirming!