@whale-av what is the difference between [bp~] and [biquad~} in this regard (2 pole 2 zero) and bandpass filter?
@gsagostinho how we could then use FFT here, is it applicable for 3 band EQ
I mentioned readsf and dac because I want to read file from hard disk and visualize it, and print because I wanted to see the out put before send it to visualizer so I get the grasp of what type of output I have so I could convert it to what I want

@bountybouncer Hello again,,
bp~ passes the frequency (1st argument) with minimal attenuation, and cuts surrounding frequencies at a rate set by the second (Q) argument. It is effectively an "inverted notch filter"

[biquad~] is more like a "variable Q tone control", as you can increase the gain at a frequency as well.
Here is a useful implementation.........4band.pd

If you want the 12 bands (and more) you can easily expand [4band.pd] and for the visualisation ((maybe)) a 30-band spectrum analyser?............ is already implemented in Pd extended...................

pd\extra\unauthorizedfilterbank~-help.pd

David.

@whale-av Thank you so much, what do you think of center frequencies range, I mean what set of numbers would best works with bp~,
I mean how do I divide frequency range for high, mid and bass

thanks indeed

@bountybouncer Hello again..
If you look at an old analogue mixing desk with 4 band parametric eq, often the bands will be... (because of the analogue filter design problems)...more or less..

Bass 40-140
Lo Mid 100-1000
Hi Mid 500-5000
Treble 1000-15000+

The even older analogue desks had fixed bands that were renowned (Midas etc.) or not (Soundcraft etc.) for their "warmth" (muddy and compressed, but "human") or "transparency" (accurate, but clinical) and which all had different fixed frequencies.
Digital desks can pretty much do anything with any band

Bass we all know
Lo Mid that we like... warmth.... is really 150-320 ish.....which includes the notes that can be sung.... up to about 1000Hz.... then that can be whistled... up to about 1800hz.... then nasty rasping aggressive treble.... up to about 7000Hz and then the finer airy sounds that float around on top.

Take your pick really, depending upon what you like personally and what you want to achieve!
David.