[FFmpeg-user] asubboost and asupercut

[Paul B Mahol]

On Fri, Nov 27, 2020 at 8:24 PM Michael Koch <astroelectronic at t-online.de>
wrote:

> Am 27.11.2020 um 19:25 schrieb Paul B Mahol:
> > On Fri, Nov 27, 2020 at 7:09 PM Michael Koch <
> astroelectronic at t-online.de>
> > wrote:
> >
> >> 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.
> >>
> > 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
> > much
> > new sub frequencies are added to the delay buffer.
>
> Sorry, I didn't understand it. I think this filter could be explained
> much better with a block diagram.
>
>
> >> -- 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 unit of the "slope" option?
>
>
1 / octave, can be set as dB unit, eg. -20dB, 0dB or 1 is max value.

Use mentioned mpv command for the reason, as it displays curve. Than you
can obviously see what slope changes.
slope is just different way to control curve, other ones is Hz, Q-factor
and octave, they all changes curve but with different output for different
value.
See documentation of other filters like lowpass, highpass, lowshelf,
equalizer and so on.