[FFmpeg-user] Frequency response of an ffmpeg equalizer filter

[Michael Koch]

Am 26.06.2020 um 19:00 schrieb Nicolas VAMBAIRGUE:
>
> Le 26/06/2020 à 18:15, Paul B Mahol a écrit :
>> On 6/26/20, Nicolas VAMBAIRGUE <nicolas2020 at nv76.info> wrote:
>>> Hello,
>>>
>>>
>>> I'm starting to use the ffmpeg filters, using the documentation. It
>>> seems working but, I don't find the way to get the frequency 
>>> response of
>>> a filter. For example, let's say I'm applying this filter :
>>>
>>> equalizer=f=7000:t=q:w=2:g=2,equalizer=f=1000:t=q:w=1:g=3,equalizer=f=80:t=q:w=2:g=-30 
>>>
>>>
>>> in the following command :
>>>
>>> ffmpeg -re -i /home/dr_click/live.wav -acodec pcm_s16be -ar 44100 -ac 2
>>> -f rtp -af
>>> "equalizer=f=7000:t=q:w=2:g=2,equalizer=f=1000:t=q:w=1:g=3,equalizer=f=80:t=q:w=2:g=-30" 
>>>
>>> rtp://127.0.0.1:1234
>>>
>>> It works, I'm hearing a distorted sound. And what I'd like to know, 
>>> with
>>> such a filter, is the db gain for the 2000 Hz signal or for the 150Hz
>>> signal or any other frequency with a query like : give me your 
>>> frequency
>>> and I'll tell you which gain is applied at this frequency with the
>>> defined filter.
>> Yes, with anequalizer filter.
>
>         => Ok, so let's say I'm using this command with an anequaliwer
>
>         =>_ffmpeg -re -i /home/dr_click/live.wav -af "anequalizer=c0 
> f=200 w=100 g=-10 t=0|c1 f=200 w=100 g=-10 t=0 curves=true" -acodec 
> pcm_s16be -ar 44100 -ac 2 -f rtp rtp://127.0.0.1:1234
>
>         => How do I get the frequency graph of such a filter ? Is it 
> mandatory to get a video stream (and how to get / display it) ? Can't 
> I get command with the frequency as input and the gain as output ? Of 
> course, such a command would means I need to query the db output for 
> each interesting frequency.

Make a test file with 2kHz sine:
ffmpeg -f lavfi -i sine=2000 -t 5 -y test.wav

Analyze the volume of this file:
ffmpeg -i test.wav -af volumedetect -y out1.wav
The volume is written to the log file.

Then apply your filter and analyze the output again.

Michael