Inversion audio filter

[Björn Sonnenschein]

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

[Carl Eugen Hoyos]

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

[Björn Sonnenschein]

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?

[Björn Sonnenschein]

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

[Elon Musk]

I think this can already be done with pan filter.

[Elon Musk]

See:

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

[Björn Sonnenschein]

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 So this request is obsolete of cause, thanks for the hint!

[Carl Eugen Hoyos]

Thank you for confirming!