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Multi-Way Conventional loudspeakers with crossovers

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Old 23rd December 2012, 08:50 PM   #31
pos is offline pos  Europe
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Quote:
Originally Posted by natehansen66 View Post
Can this be done in a single impulse, or will there have to be phase correction for each channel separately?

I use J River's convolver but am having issues with their loopback using multi-channel convolution (I used rePhase to generate linear filters for my 3-ways), but others report that 2 channel convolution works fine. I'd like to build my crossovers in JR's PEQ and do the phase linearization if possible with a single impulse.
As Thierry pointed out only a stereo convolution with phase-only correction in front of an IIR filter should be enough if your (acoustical) filters are phase coherent.

If you use JRiver you can do the whole filtering with rephase without resotring to IIR filtering. Here is a small tutorial written by Jimmy Thomas that describe how to do it:

http://jimmy.thomas.free.fr/Jriver/T...olmImpulse.pdf

It is in French but here is an automated translation (the picture are missing so it needs to be read alonside the opriginal version...) :
Google Translate

(in french only, sorry, but maybe some online translation tool will be able to
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Old 23rd December 2012, 09:13 PM   #32
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Originally Posted by twest820 View Post
It's not well known, but the ES9016 and ES9018 DACs support user specified antialiasing filters. One interesting use of rePhase is to explore what sort of constrained phase response filters could be programmed into these DACs. However, this is difficult with the 0.9.2 build as it's limited to a maximum sampling rate of 192kHz and a maximum frequency in the response graph of 30kHz.

pos, if you could

1) add 352.8kHz, 384kHz, 705.6kHz, 768kHz, 1.4112MHz, and 1.536MHz to the list of supported sampling rates
2) add an option to select or specify the graph's maximum frequency (a checkbox for 30kHz versus Nyquist would be sufficient, though more granular control would be nice)

checking out these design possibilities would be quite a bit easier since the relevant sampling rate could be specified and the response seen. I'd make this change but I don't see source code available at sourceforge.
Ok I will try to add these in the next version!
What format would you need? 32 bits IEEE754? txt file?
What are the exact frequency values in Hz?
Extending the graph range will be more difficult (it is fixed right now), but I will work on it.
I need to find some time and motivation to work on rephase again.

I would also like to add an oversampling feature to reduce the ripples Barleywater has noted.

As for the source code, it is not clean enough to be published yet I'm afraid
It was a test bench as well as a software, and adding features (and A GUI!) over and over in this configuration rapidly leads to something no one would be proud of
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Old 23rd December 2012, 09:33 PM   #33
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Know the feeling; I have some binaries in the public domain I hope people never see the sources for. They were written early in my career and have some embarassing noob things in the code.

Thanks for the sampling rate adds. Those are the exact frequency values---they're just 8, 16, and 32x in the usual 44.1 and 48 series. The output formats already supported should be fine.
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Old 23rd December 2012, 10:38 PM   #34
Pano is offline Pano  United States
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Twest, how are you getting the functions into the DAC? I think I have a few ES9016 implementations kicking around here and would like to try it.
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Old 23rd December 2012, 11:23 PM   #35
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I've replied over in the ES9016 thread as the fiddly details of ESS DAC configuration are kind of out of scope to rePhase.

Last edited by twest820; 23rd December 2012 at 11:36 PM.
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Old 23rd December 2012, 11:40 PM   #36
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Just how long does the impulse response have to be (samples) to have any accuracy at low frequerncy?
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Old 23rd December 2012, 11:44 PM   #37
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JRiver like at least 1 second, tho I'm not sure why.
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Old 23rd December 2012, 11:49 PM   #38
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Originally Posted by Pano View Post
JRiver like at least 1 second, tho I'm not sure why.
?

Length should not depend on convolver. It's a matter or frequency resolution.
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Old 23rd December 2012, 11:50 PM   #39
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I just know that JRiver asks for a 1 second impulse length - but it works with less. Maybe it's not a frequency requirement, but a room EQ thing.
FWIW, I can never get an exact match in the bass, say below 30Hz, when exporting and re-importing an impulse in HOLM. Even at +/- 10K samples and seeing nothing out that far.
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Old 24th December 2012, 12:14 AM   #40
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Originally Posted by Pano View Post
I just know that JRiver asks for a 1 second impulse length - but it works with less. Maybe it's not a frequency requirement, but a room EQ thing.
FWIW, I can never get an exact match in the bass, say below 30Hz, when exporting and re-importing an impulse in HOLM. Even at +/- 10K samples and seeing nothing out that far.
Yes, 10k samples at 48k sampling only gibe 4.8 Hz resolution and, as you note, you are probably not going to get the kind of accuracy needed from a measurement where the noise floor is maybe -50 or 60dB at best. That is a problem and it gets worse as the sample rate goes up.
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