Opened 5 years ago

Closed 5 years ago

#2389 closed enhancement (invalid)

Inversion audio filter

Reported by: sun Owned by:
Priority: wish Component: avfilter
Version: unspecified Keywords:
Cc: Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no

Description

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

Change History (8)

comment:1 Changed 5 years ago by cehoyos

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

comment:2 Changed 5 years ago by 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

comment:3 Changed 5 years ago by 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?

comment:4 Changed 5 years ago by sun

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

comment:5 Changed 5 years ago by richardpl

I think this can already be done with pan filter.

comment:6 Changed 5 years ago by richardpl

See:

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

comment:7 Changed 5 years ago by 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 So this request is obsolete of cause, thanks for the hint!

comment:8 Changed 5 years ago by cehoyos

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