[FFmpeg-user] asubboost and asupercut

Paul B Mahol onemda at gmail.com
Fri Nov 27 20:25:35 EET 2020

On Fri, Nov 27, 2020 at 7:09 PM Michael Koch <astroelectronic at t-online.de>

> Hello,
> I have a few questions about the asubboost and asupercut filters.
> -- In asubboost it's not yet clear how the block diagram of the filter
> looks like. Especially the "decay" and "feedback" options are unclear.
> What's the input of the the delay line? Before or after the low pass
> filter? Where does the feedback go to? Before or after the lowpass
> filter? I have attached a sketch of a possible block diagram, but it's
> only a wild guess.
> -- What's the unit of "delay"? Is it milliseconds? Or is it audio samples?

This filter just adds delayed sub frequencies set by cut off frequency back
to output. Decay sets decay of old sub echo in buffer and feedback sets how
new sub frequencies are added to the delay buffer. Delay is set in 1/1000

> -- Is it correct that the "slope" parameter effectively changes the
> cutoff frequency, but doesn't change the steepness (dB / octave) of the
> filter?

It changes steepness, not cutoff.

> -- What's the difference between "asupercut" and "lowpass" filter?
> What's the filter steepness of the asupercut filter?

Very big, almost under 90 deg.

You can find out filter graph response for almost any filter combination in
Using this filter graph:

mpv av://lavfi:aevalsrc="not(mod(n\,32768)):d=50" -lavfi-complex

In place of asupercut you can put any combinations of FIR and/or IIR
filters: lowpass, bandpass, ..., aiir, afir, acrossover and so on.

> Michael
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