[FFmpeg-user] Audio normalization using "volume" and "compand"filters

[Paul B Mahol]

On 11/28/13, Thierry Lelegard <thierry at lelegard.fr> wrote:
>> De: "Paul B Mahol" <onemda at gmail.com>
>> On 11/27/13, Thierry Lelegard <thierry.lelegard at free.fr> wrote:
>> > Le 27/11/2013 21:49, Paul B Mahol a ecrit :
>> >  > On 11/27/13, Thierry Lelegard <thierry at lelegard.fr> wrote:
>> >  >
>> >  >> Second problem: The usage of the filter "compand" is extremely
>> >  >> obscure.
>> > Its
>> >  >> documentation (http://ffmpeg.org/ffmpeg-filters.html#compand)
>> >  >> can hardly
>> > be
>> >  >> understood if you do not already know the meaning of each
>> >  >> parameter.
>> > See
>> >  >> below some tests I made without deeply understanding what they
>> >  >> mean.
>> >  >>
>> >  >> [....]
>> >  >>
>> >  >> Could someone please explain how to use "compand" and its
>> >  >> parameters?
>> >  >>
>> >  >> More precisely, how can we compress an input audio with the
>> > characteristics
>> >  >> in_rms and in_peak into a given target out_rms and out_peak?
>> >  >
>> >  > compand filter is port of sox effect filter of same name.
>> >  > I really doubt that its documentation is obscure.
>> >
>> > This is of course a subjective matter. To make it more objective,
>> > the
>> > following
>> > is a complete copy/paste of the "compand" documentation from
>> > http://ffmpeg.org/ffmpeg-filters.html#compand
>>
>> Why are you pasting documentation? To show you can copy & paste?
>
> No, it was to show you the documentation because when you wrote
> "I really doubt that its documentation is obscure" it was obvious
> you did not read it.

I wrote that documentation.

>
>
>> > Honestly, how can you get an answer to the above question ("how can
>> > we
>> > compress an input audio with the characteristics in_rms and in_peak
>> > into
>> > a given target out_rms and out_peak?"), using this when you are not
>> > an
>> > expert in audio engineering?
>>
>> rms and peak are calculated using whole file, so whatever you are
>> trying to do you are doing it wrong.
>
> I know that what I am doing is wrong. Otherwise I would get the expected
> result and I would not have posted on the list in the first place.
>
> Considering that my question was somewhat specific ("how can we
> compress an input audio with the characteristics in_rms and in_peak
> into a given target out_rms and out_peak?"), it would be more
> constructive to provide an answer. Simply replying "you are wrong"
> brings no information since we all already know that.

compand filter is used to compress/expand audio dynamic range.
What you want to do and results you expect is imho more suited for
volume filter.

>
> -Thierry
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