BruteFir integration

[bitlab]

The CAPS project EqFA4p filters makes use of a bw (bandwitdh) parameter instead of the Q factor.
In the past a few asked question about the exact meaning of bw, but I didn't see the answer.
Did anybody make progress on that 

It look like it doesn't match at the classic form as in:
    bw = fc /Q. Where the bandwitdh is the difference in the upper and lower frequentie at -3 db from fc.

Attached is a measurement with:
fc= 1kHz, gain = 6 db, overall gain -3db  and a bw parameter of 0.5 and 1.

It seems that the EqFa4p bw parameters more looks like the classical bw/2.
Pratical that means that Q can't be higher then 4 (lower limit of the filter is bw=0.125)

If we do the math the following table gives an identication about how Q relates to bw parameter of eqfa:

Code:

fc=1000.00Hz Q=8.00 bw=0.12 fl=939.5 fh=1064.5 fd=125 bw_eqfa=0.06
fc=1000.00Hz Q=4.00 bw=0.25 fl=882.8 fh=1132.8 fd=250 bw_eqfa=0.12
fc=1000.00Hz Q=2.00 bw=0.50 fl=780.8 fh=1280.8 fd=500 bw_eqfa=0.25
fc=1000.00Hz Q=1.00 bw=1.00 fl=618.0 fh=1618.0 fd=1000 bw_eqfa=0.50
fc=1000.00Hz Q=0.50 bw=2.00 fl=414.2 fh=2414.2 fd=2000 bw_eqfa=1.00
fc=1000.00Hz Q=0.25 bw=4.00 fl=236.1 fh=4236.1 fd=4000 bw_eqfa=2.00
fc=1000.00Hz Q=0.12 bw=8.00 fl=123.1 fh=8123.1 fd=8000 bw_eqfa=4.00

Now at least we can calculate the correct parameters from the AutoEq project to setup EqFa4p based filters, like the EqFa12p.