Thanks, Andy,
„recursive vs. nonrecursive”
– it depends how your IIR is created. If it is using a double precision and not a simplest s-z transform, there is nothing to say about IIR (serious DAWs in studio). But DSPs in car audio head units is much different story. Alexander Martyanov (his nick is „martyanov” here and he has beautiful build log here and he is two times EMMA European champion Sergey’s engineer) told me his experience with usage of head unit equalizers and this experience is not good for that equalizers. And proximity of Nyquist frequency for FIR is nothing in opposite to IIR.
FIR equalizer may have ordinary parametric equalizer interface and may be used just as parametric.
I got a lot of compliments from pro (concert, studio) clients (I was not specially asking them) how „light” is sound of such FIR parametric. And they asked „can we get such quality into DAW plagin” : )
Most important advantage of FIR is that you have ability to use virtually any (unlimited) number of different equalizers same time but still having just a one FIR engine. For example 1) accurate loudspeaker correction equalizer, 2) parametric 1., 3) parametric 2., 4) time domain delay equalizer, 5) Hi and Low timbre for taste, 6) parametric 3. for final tweak, 7) parametric 4. for ... and so on...
And no degradation by switching on new additional EQ.
„we don't listen to minimum phase systems”
– 90% of problems in loudspeakers is minimum phase problems and can be ideally (amplitude and phase) corrected by minimum phase equalizer. Non minimum phase problems may be caused only by inaccurately tuned crossover. But let’s tune it as accurately as we can. Especially if we have possibility to „see” delays between different bands by use of TDA. And, if we are still not happy with such result, let’s use a frequency dependant delay correction. Sorry for returning to previous example of Quested monitors:
delay estimation and measurement
„I hope you know that you don't need to flatten every peak”
- sorry, I did not read books and forums and now this : ), but it is true for 1. attachment picture in post #11. And it is not true for 2. attachment picture.
Just in few past years we have offers of dsp units with FIRs for car audio. But story is same as with professional BSS processors that offered FIRs much early (and it was much, much early offered by yours faithful servant). When I asked them how to use they FIRs, what to upload to them, the answer was – we don’t know.
Serious reason to use FIR is just in one case - when we have very accurate and detailed information (curve) of a loudspeaker performance. And 10 years experience shows that we can obtain this only by working in power domain (with some similarity with microwave engineering, where system parameters are distributed, not lumped and systems are described with much more poles then four, and we talk not about voltage and currant but about power – the loudspeaker is the same from a wave theory prospective)
And another serious reason to use FIR is because of FIR ability to follow any curve we like and as accurate as we like. We may spend hours of our time to try to recreate some curve by use of parametrics. And this will be just an approximation anyway, a raw approximation.
“If phase correction isn't an inherent feature of an FIR-based DSP engine, then I like knowing that, I was under the mistaken impression that using FIR filters were giving you an automatic positive in that it didn't mess with phase, or the phase you got in, is what you got out.”
- FIR is allowing to do anything with phase independently regarding amplitude. And it is completely your responsibility what to do. My first suggestion is to use minimum phase filters that are doing phase correction based of properties of minimum phase systems.
“…like rise time in amplifiers, or slew rate on op-amps.” - it is about non linear behavior (non linear distortions) of the system that is creating new additional components in signal. It is some kind opposite to linear distortions that is not creating new components but is changing relationship of existing components of the signal.