BruteFir integration

[bitlab]

[quote pid='27053' dateline='1604855250']

@Coustard to migrate existing settings:  Q = 0.5 / BW  (where BW is the EqFa filter bandwidth, not general bandwidth)

Actually, and at the risk of sounding ungrateful, are you sure? I know this is an oft-quoted conversion but I've just spent an afternoon capturing EQ curves from moOde6 .71 in REW and it doesn't look right.

Methodology: 
1. Play white noise from moOde, set a single band of EQ to +10dB at 1kHz at various bandwidths and capture averaged (16x) RTA curves in REW. 
2. Play white noise in Apple Logic (DAW), set a single band of built-in EQ to +10dB at 1kHz at various Q factors and capture as above.
3. Visually match curves (example attached)
4. Tabulate.

I should say that I tried a variety of Eqs in Logic ('standard' types rather than Ye Olde recreations) to confirm kind of consensus on curve shape and they all basically agreed.

Results (moOde BW v Logic Q):
0.2      3.8
0.3      2.6
0.4      1.9
0.5      1.5
0.6      1.3
0.7      1.1
0.8      1
0.9      0.93
1         0.79
1.1      0.75
1.2      0.71
1.3      0.67
1.4      0.6
1.5      0.54
2         0.4

My undergraduate maths is too rusty to work out the relationship but it's plainly not linear. Assuming the maths involved is the same for the new 12-band Eq then this will work okay for me as a look-up table, but it would be nice to have an equation.

Varying gain changes things a bit too - moOde's eq becomes slightly broader than Logic as I reduce band gain but I can live with that.

There's some interesting stuff at http://www.sengpielaudio.com/calculator-bandwidth.htm but their equations still don't produce what I'm seeing in REW.

As I said, I don't want to appear ungrateful - it's great to have the facility and this is more about curiosity than anything else.

On the contrary, I am grateful that someone else also took a look at it :-)

To prevent clutter of the release hread;  shall we take the discussion to an other exsiting thread http://moodeaudio.org/forum/showthread.p...316&page=3 ?
I have also added there one of my measurements. Also I have some issue with gain when I combine multiple filters I see an issue with the gain, see the result there.

[/quote]

Used tools:

• RightMark Audio Analyzer 6.4
  
• Equalizer APO 1.2.1 as reference for the frequency response of a parametric EQ.
  

My test procedure:

• Generate with RightMark Audio Analyzer a test WAV with calibration signal and a sine wave sweep for 16bit 44.kHz.
  
• Play the test signal with a test source (moOde or APO).
  
• Record the signal with RightMark Audio Analyzer.
  
• Analyze the recorded signal with RightMark Audio Analyzer.
  

The signal stays in digital domain with use of only SPDIF.