Glad to see some continuing activity in this thread, as I'm very interested in what you've done too.
Please correct observations I've made, as I try to replicate your results with the more limited tool set I have for FIR generation.
First, it looks like from the linear scale impulse responses, that your desired & corrected target curve for the AMT-920 is IIR/minimum phase.
So you're using FIR to replicate IIR? Correct?
That would make sense to me, considering I think you are showing this example as a proxy for a full-range "system example", in which case I know we would not want a linear phase high-pass filter.
What is the high-pass target...looks like maybe a higher order Bessel?
And what is the low-pass target? It's so steep I'm thinking it almost has to be linear-phase???
Do you have a handy phase plot of the corrected results?
Thx, that info will help me continue to experiment along with trying to improve ETC curves for the same type example.
Tangential to the subject at hand, in 2004 Peter Craven wrote a paper about apodizing filters designed to reduce pre-ring and shorten impulse response. https://secure.aes.org/forum/pubs/journal/?elib=12992
Unfortunately his technique requires a reduction in high frequency bandwidth, but the general concept may be enlightening.
Unfortunately his technique requires a reduction in high frequency bandwidth, but the general concept may be enlightening.
D
Deleted member 375592
Yes.
Correct, Theoretically, we can use it but practically, AFAIK, there are no benefits to using a symmetric FIR. Using traditional LR4 or minimum-phase FIR appears preferable. Keep in mind that DSP implementations of IIRs tend to suffer from many numerical problems; we have to convert an IIR to a cascade of low-order state-space sections, etc. It took Sirrus Logic about 10 years to finally produce good anti-aliasing IIR filters.
first order, it matches - more or less - the driver without non-idealities
It's a 4th order Butterworth. it matches - more or less - the driver without non-idealities
No, I don't. Matlab's phase plots are of questionable value.
Thanks for all that. I should have seen first order matches, but the FIR generator i was using starts with 2nd order (made for live sound).
And can see the fourth order Butterworth fits well too.
Here's the kind of ETC I can get from a B&C dcx464 coax CD, using the HF section as my proxy for a speaker system.
With an IIR high-pass target, faintly seen as blue under the green magnitude trace.
So in comparison, your proxy speaker ETC look awesome to me !!
(I do have a lot of in-room noise no way to get rid of)
I do really like linear-phase xovers....particularly steep ones, like 96dB/oct. Probably because all my builds are usually 5-ways, and the steep filters give so much latitude in choosing crossover frequencies that stay within drivers' regions of relatively flat response. I've found relatively little impulse inversion is required to correct the meat of a drivers passband vs out of band. And the linear-phase portion of the FIR filter is then dominated by just the crossover.
Which for me means, any pre-ring is mainly due to lack of acoustic complementary from off-axis lobing.
(I personally can't imagine giving up lin-phase crossovers
And can see the fourth order Butterworth fits well too.
Here's the kind of ETC I can get from a B&C dcx464 coax CD, using the HF section as my proxy for a speaker system.
With an IIR high-pass target, faintly seen as blue under the green magnitude trace.
So in comparison, your proxy speaker ETC look awesome to me !!
(I do have a lot of in-room noise no way to get rid of)
I do really like linear-phase xovers....particularly steep ones, like 96dB/oct. Probably because all my builds are usually 5-ways, and the steep filters give so much latitude in choosing crossover frequencies that stay within drivers' regions of relatively flat response. I've found relatively little impulse inversion is required to correct the meat of a drivers passband vs out of band. And the linear-phase portion of the FIR filter is then dominated by just the crossover.
Which for me means, any pre-ring is mainly due to lack of acoustic complementary from off-axis lobing.
(I personally can't imagine giving up lin-phase crossovers
Yes, in the context of ADC decimation and DAC interpolation filters. Basically a predecessor of his MQA work, but without licensing costs or lossy compression. I don't hear any difference between the steep and apodizing filters I put in my DAC, but that could very well say more about my hearing than about the concept. It's certainly interesting.