[FFmpeg-user] sidechain compression: NOT ducking, but envelope

[Michael Werzowa]

Thank you, I will have a look.
And I will contact you directly, if this is ok?
Best regards,
Michael
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Michael Werzowa
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mikey at werzowa.at
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> Am 2024-11-18 um 13:07 schrieb Paul B Mahol <onemda at gmail.com>:
> 
> There is no standalone envelope filter in FFmpeg, but there is one in
> Librempeg. (If envelope is standard definition by audio community)
> 
> If you already have smooth envelope, you can use in FFmpeg
> sidechaincompress filter (takes two input streams) + amix filter.
> 
> I could help more if I can look at that py code that works.
> 
> 
> Also see lavfi-preview tool, it can help building (complex) filter graphs
> within GUI.
> 
> On Mon, Nov 18, 2024 at 10:05 AM Michael Koch <astroelectronic at t-online.de>
> wrote:
> 
>> Am 18.11.2024 um 09:32 schrieb Michael Werzowa via ffmpeg-user:
>>> Dear List,
>>> 
>>> I am new to the list. Searched the last two years of the list for
>> „sidechain“, and did not find a hint.
>>> My usecase:
>>> Using an audio file to provide an envelope, that is applied to another
>> audio file, modulating the gain of this file.
>>> With ffmpeg I easily can manage „ducking“, via direct call and using the
>> python interface, but with my use case I run into errors or get the wrong
>> output.
>>> For music mixing, this would be a typical use of sidecahin compression.
>>> ChatGPT 4o and Claude 3.5 Sonnet gave me a lot of advice, which all lead
>> to the same: either the wrong effect, or an error.
>>> 
>>> An example that does NOT work, although it should be the thing I want:
>>> 
>>> ffmpeg -i data/to_be_modulated.wav -i data/sidechain.wav -filter_complex
>> "[1:a]aformat=sample_fmts=fltp:sample_rates=44100:channel_layouts=stereo,volume=2,highpass=f=20,agate=mode=downward:threshold=0:ratio=1:attack=0.0057:release=0.02:range=60:makeup=1[env];[0:a][env]amultiply"
>> data/output-processed.wav
>> 
>> I think this can only work if [env] is a unipolar (always positive)
>> signal. I doubt that it is. Write the output of the agate filter to a
>> file and have a look at this signal.
>> 
>> Michael
>> 
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