BruteFir integration

[jijopujolo]

@jijopujolo if you can find that reference back it would be very helpfull ?

I used now the bandwith calculations from https://www.audiorecording.me/parametric...s.html/amp, but those outcomes differs ~ 2x from the actual used bw of EqFa4p.

Anyway to ease use the configuration interface is now using Q instead of bw. It would be great to have more well-founded Q calculation.

The first try yielded nothing, but I'll look harder.
What I gathered at the moment are only indirect/oblique references such as:

1. https://www.superbestaudiofriends.org/in...ost-143291
   
2. https://www.head-fi.org/threads/measurem...t-14087626
   
3. https://gist.github.com/tresf/5f6cbd86f6...diff-L4339
   

Just to be clear, if I understand correctly you're using the bandwidth in Hertz (f/Q), while my assumption was to use the bandwidth in octaves (N).

Relation between Q and N:

N = ln(1 + 1/(2*Q^2) + sqrt(((2*Q^2 + 1) / Q^2 )^2 / 4 - 1)) / ln(2)

(source: AutoEq usage page)

Some values:

Q -> N (bandwidth in octaves)
8 -> 0.1802
4 -> 0.3597
2 -> 0.714
1 -> 1.3885
0.5 -> 2.5431
0.25 -> 4.1655
0.12 -> 6.1585

source:
http://www.sengpielaudio.com/calculator-bandwidth.htm

I have no idea if these values would make sense in EqFA4p.

Some additional references:
https://www.ranecommercial.com/legacy/note170.html
http://www.sengpielaudio.com/Umrechnungs...Filter.pdf

I seldom use equalizers, but when I do I use AutoEq* as a reference, so having Q in the GUI would be wonderful.
*: at the moment I'm using bmc0's system wide dsp and while I'm happy with the results and I have a commandline switch between my presets, I certainly miss a GUI

Disclaimer: I'm way out of my field of expertise, so please forgive me if I'm just wasting everybody's time.

Would that this were a simple subject, but designing digital audio filters is anything but.

Amen to that!