[FFmpeg-user] asubboost and asupercut

[Paul B Mahol]

On Sat, Nov 28, 2020 at 2:46 PM Paul B Mahol <onemda at gmail.com> wrote:

>
>
> On Sat, Nov 28, 2020 at 2:24 PM Michael Koch <astroelectronic at t-online.de>
> wrote:
>
>> Am 28.11.2020 um 13:44 schrieb Paul B Mahol:
>> > On Sat, Nov 28, 2020 at 1:35 PM Michael Koch <
>> astroelectronic at t-online.de>
>> > wrote:
>> >
>> >> Am 28.11.2020 um 12:57 schrieb Paul B Mahol:
>> >>> On Sat, Nov 28, 2020 at 12:41 PM Michael Koch <
>> >> astroelectronic at t-online.de>
>> >>> wrote:
>> >>>
>> >>>> Am 27.11.2020 um 20:50 schrieb 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.
>> >>>> I did try to reverse engineer the asubboost filter from its output
>> >>>> signal. Is the attached sketch correct?
>> >>>> It seems the "feedback" parameter is unnecessary because it does
>> exactly
>> >>>> the same thing as "wet".
>> >>>>
>> >>> No, your reasoning is invalid.
>> >>>
>> >>> I do not have time to draw graphs or do consulting for free.
>> >> When you swap the values of "wet" and "feedback", the output does
>> always
>> >> remain the same.
>> >> If you think that I'm wrong, please show an example to prove the
>> opposite.
>> >>
>> > Make sure that you take into account decay parameter, delay buffer is
>> still
>> > used.
>>
>> When you swap the values of "wet" and "feedback", the output does always
>> remain the same, regardless which values you use for "dry", "decay" and
>> "delay".
>> As can be shown with this example:
>>
>> set "A=0.4"
>> set "B=0.7"
>>
>> ffmpeg -f lavfi -i aevalsrc='0.5*gt(t,0.1)':d=1 -lavfi
>> asplit[a][b];[b]asubboost=dry=0.3:wet=%A%:decay=0.4:feedback=%B%:delay=50[c],[a][c]join,showwaves=draw=full:s=800x300:r=1
>>
>> -frames 1 -y out1.png
>>
>> ffmpeg -f lavfi -i aevalsrc='0.5*gt(t,0.1)':d=1 -lavfi
>> asplit[a][b];[b]asubboost=dry=0.3:wet=%B%:decay=0.4:feedback=%A%:delay=50[c],[a][c]join,showwaves=draw=full:s=800x300:r=1
>>
>> -frames 1 -y out2.png
>>
>> ffmpeg -i out1.png -i out2.png -lavfi vstack -y out.png
>>
>>
>> Red is input step signal, green is output step response of the asubboost
>> filter. In the lower half of the output image the "wet" and "feedback"
>> values are swapped.
>>
>
> What we said previously about delay buffers and that above command?
> It was literally less than 24h.
> That command can not show you the action of delayed input as it is not
> designed for it.
>

More precisely input which is single impulse and rest is 0 can not give you
different output ever.
Try it on real bassy music.


>
>>
>> Michael
>>
>> _______________________________________________
>> ffmpeg-user mailing list
>> ffmpeg-user at ffmpeg.org
>> https://ffmpeg.org/mailman/listinfo/ffmpeg-user
>>
>> To unsubscribe, visit link above, or email
>> ffmpeg-user-request at ffmpeg.org with subject "unsubscribe".
>
>