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Multi-Way Conventional loudspeakers with crossovers

rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
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Old 14th January 2017, 09:02 AM   #1501
Raimonds is offline Raimonds  Latvia
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Quote:
Originally Posted by pos View Post
The APL1S is a very interesting box, with versatile (and probably very good quality) I/Os and 4096 taps at hand (vs 6144 for the openDRC).

My biggest grip with it is the fact that the convolution is done with 24bit fixed points FIRs. This is fine for speaker correction (the intended target of the box) but can be a problem with filtering.
Hi,
Is it mean that 120 dB stopband`s attenuation is not enough for you : )))?
What is the problem which is requesting that?
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Old 14th January 2017, 06:55 PM   #1502
pos is offline pos  Europe
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Hello Raimonds,

No mean to disrespect your work or disparage your product, as it looks really good and professional, and is one of the rare hardware convolution engines out there

I just feel float arithmetic would have been a better choice for filtering (which, again, is not the intended purpose of your box if I understand correctly).
The curves in the post above are what happens with a 1kHz filter and 0dBFS passband.
The stopband level will be higher with a lower crossover point and/or with attenuation.
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2019-01-16: rePhase 1.4.3
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Old 15th January 2017, 08:56 AM   #1503
Raimonds is offline Raimonds  Latvia
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Hi POS,

Thank you! I am offering detailed EQ (available only on FIR) for 15 years.
The last 12 - on hardware.

Your mentioned stopband attenuation does not depend on bit number and will be the same for any filter tuning frequency but with "but" if you have unlimited number of fir filter coefficients.
We have limited number in the real life. Your mentioned example of filter on 1 kHz will be much higher affected by real length of fir filter instead of the bit number of its coefficients.
Please run your simulation for real length and you will see that it affects the stopband much higher than the bit number. And it highly depends on your skills to cut the filter to the length you need/have.


You can use any of APL`s FIR products for filtering / crossover functions with very high success.

But you should catch what is the most serious advantage of APL`s offers.
That advantage makes the job of sound producer / director / recording engineer two times more efficient ...
The first step should be to implement that for everyone who has serious passion in audio quality.

Good luck,
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Old 15th January 2017, 10:07 AM   #1504
pos is offline pos  Europe
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Very high stopband rejection can be obtained with a good choice of windowing algorithm, independently of the number of taps :

4096 taps @ 48kHz, Albrecht 8-term window, 32 bits float:
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool-rephase-4096taps-float-png

4096 taps @ 48kHz, Albrecht 8-term window, 24 bits fixed:
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool-rephase-4096taps-24bits-png
Attached Images
File Type: png rephase 4096taps float.png (41.6 KB, 577 views)
File Type: png rephase 4096taps 24bits.png (45.3 KB, 572 views)
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Old 15th January 2017, 12:35 PM   #1505
Raimonds is offline Raimonds  Latvia
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Such windowing removes all the steepness / selectivity of the filter.
Why should we use an expensive digital FIR filter in such case?
An analog filter is pretty good for that. Or even much better : )
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Old 15th January 2017, 12:50 PM   #1506
pos is offline pos  Europe
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I am not sure I follow your argument here: are you implying that your unit does not have enough taps to do filtering with more than -90dB rejection, and that an analog device is a better choice?...

That 50Hz low-pass filter shown here is around 36dB/oct up to -20dB, then 48dB/oct up to -40db, and keeps increasing in slope after that. Quite usable I would say, and with linear phase

But that is beyond the point: 24bit fixed is enough for EQs, and that is what you do, apparently with great success.
32bit float is IMO a better choice when filtering is involved.
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Old 15th January 2017, 01:56 PM   #1507
Raimonds is offline Raimonds  Latvia
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Yes, the analog crossover is better choice even we are "dancing" around the liner phase.
Your mentioned example is very close to 4th order analog filter.
It is extremely expensive to try to build a 4 way system using 4 FIR filters for crossover and only for the goal to have the linear phase crossover.
Much elegant solution is to use the analog crossover and then just one FIR filter to make its phase linear . FIR filter can serve not only mentioned time correction`s function but any other EQ functions you like in such case.
And it is extremely easy to make a phase correction for your crossover.
Measure or calculate its IR. Inverse it in time. Upload to your FIR. This filter is completely bit insensitive. Even 16 bits will be ok.

Last edited by Raimonds; 15th January 2017 at 02:20 PM.
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Old 15th January 2017, 04:16 PM   #1508
Oabeieo is offline Oabeieo  United States
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I have a 4 way FiR crossover and it wasn't that much expensive.

3 minidsp 2x4HDs ( 2 of them used as a 2x2)

It actually works quite well in fact I think I paid less for all three than a single APL would have cost. IIRC or very close to . And I can make that 50hz horbach crossover or whatever it is no problem.

Last edited by Oabeieo; 15th January 2017 at 04:23 PM.
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Old 16th January 2017, 05:09 AM   #1509
Raimonds is offline Raimonds  Latvia
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Hi,
What was your reason to use FIRs for crossover?
The most serious reason to have FIRs as crossover filters is the goal to have detailed EQ on each of bands. Are you able to arrange that?
How do you implement the master EQ for your system?

APL has lot of different APLs ... : )
There are no competitors for APL1s unit in terms of quality.

Last edited by Raimonds; 16th January 2017 at 05:16 AM.
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Old 16th January 2017, 01:45 PM   #1510
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Quote:
Originally Posted by Raimonds View Post
Yes, the analog crossover is better choice even we are "dancing" around the liner phase.
Your mentioned example is very close to 4th order analog filter.
It is extremely expensive to try to build a 4 way system using 4 FIR filters for crossover and only for the goal to have the linear phase crossover.
Much elegant solution is to use the analog crossover and then just one FIR filter to make its phase linear . FIR filter can serve not only mentioned time correction`s function but any other EQ functions you like in such case.
And it is extremely easy to make a phase correction for your crossover.
Measure or calculate its IR. Inverse it in time. Upload to your FIR. This filter is completely bit insensitive. Even 16 bits will be ok.
Yes, that was the initially the sole purpose of rephase
But FIR filtering can bring many other things beside simple phase linearity, like the H-K crossover Oabeieo mentioned above.

Now if we are talking about optimization and opportunities to mix FIR and IIR, why not implement Balázs Bank's automated method with biquads in your solution to make better use of the coefficients your hardware can provide (ie better frequency resolution), and possibly keep a short FIR just for phase linearization?...

There are many ways to achieve good results. I personally like the idea of doing everything with one time domain convolution with a (floating point ) FIR: very simple and brutally elegant
And the good news is that it can already be done today, and things will only get better in the coming years thanks to companies offering opened solutions like yours, miniDSP, Marani, Powersoft, etc.
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