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

[Michael Koch]

>>>
>>>         => 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
>
>
>         => Thank you again for your answer Michael but, I think I 
> probably didn't expressed my question with the right words. Let's 
> forget the file in and the file out to focus only on the filter : 
> "anequalizer=c0 f=200 w=100 g=-10 t=0|c1 f=200 w=100 g=-10 t=0"
>
>         => What I want to know, before applying any input signal is 
> the result of this mathematical function : f(frequency) = gain. For 
> example, this filter is centered on 200 Hz with a bandwith of 100Hz 
> and a gain of -10 db. So, all the 200Hz frequencies will be attenuated 
> by -10 db. But what for the 250Hz frequencies in the signal ? Still 
> -10 db ? Or -9 ? Or -7.5 ? Same question for the 350 Hz frequencies in 
> the signal.
>

Unfortunately the filter steepness is undocumented. I don't know if 
ffmpeg can analyze the filter curve for all frequencies at the same 
time. I have no other idea than analyzing one frequency after the other.

Michael









> => The result given like a mathematical function, a cloud of dots, an 
> image or anything else that could help me to draw such a graph : 
> https://s1.qwant.com/thumbr/0x380/0/5/cfb0ceac6e3b4fdd73923eaaf68e76c58991b4de8ac088f4dfad665d5b8c34/parametric.png?u=https%3A%2F%2Fcdn.tutsplus.com%2Faudio%2Fuploads%2Flegacy%2Fqt_040_eq%2Fparametric.png&q=0&b=1&p=0&a=1
>
>         => I wish my question is more clear now.
>
>         => And thank you again for your answers and your help :-)
>
>>
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   ASTRO ELECTRONIC   Dipl.-Ing. Michael Koch
        Raabestr. 43   37412 Herzberg
           www.astro-electronic.de
   Tel. +49 5521 854265   Fax +49 5521 854266
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