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Multi-Way Conventional loudspeakers with crossovers

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Old 25th December 2012, 10:26 PM   #51
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Quote:
Originally Posted by pos View Post
Donwsampling can only be used when doing an active crossover.

First let me say I'm all for what you are doing. I'm just commenting on technical issues.


It's not that easy to just say down sample. Down sampling assumes that the frequency content of the output of the filter is not important. That is, there is no information in the output above the Nyquist frequency of the new sample rate. That may be true for steep filters but not necessarily so for filter with shallower slopes. And developing algorithms for crossovers with down sampling and FFt convolution and getting everything in sync are all that common place. In fact the Four Audio stuff is the only one I have seen doing this, not that I have followed these developments all that closely.

What your are doing will probably be very useful with something like the miniDSP Open DRC platform. But it's a brute force convolution engine. You are just generating the impulse responses required and have no control over the convolution algorithms being used in the hardware actually doing the filtering.

Four Audio says, " The necessary length and hence number of coefficients of a FIR filter to reach satisfactory spectral selectivity scales with wavelength. If not handled by overlapped FFT convolution techniques, an FIR filter dedicated for the mid, low or sub band has to be run at a reduced sample rate to spare DSP resources." But they also say, "Max. frequency resolution: 3 Hz". I don't know what convolution algorithm they are using (sounds like brute forces as well). Boidzio UE uses partitioned, FFT convolution and is pretty fast with 8192 taps but does loose accuracy at low frequency.

Also, I have no idea what the Four Audio HD2 costs. It looks interesting. Can the impulse from your software be imported to it?

The miniDSP DRC is $300 and it appears your impulse can be used. The PC based Bodzio UE is $150 plus about $100 for a suitable sound card and it can generate the impulses it needs and convolve them with the audio signal.
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Old 25th December 2012, 11:32 PM   #52
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VSTconvolver plugin is free,fft partitioned multi convolution engine too.

FIR EQ/crossover +DRC+phase linearizaton pc based
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Old 26th December 2012, 02:42 AM   #53
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Originally Posted by john k... View Post
Also, I have no idea what the Four Audio HD2 costs. It looks interesting. Can the impulse from your software be imported to it?
I asked Rainer Thaden and he send me the price list last year: the 2x8 module (to be mounted in a box) is around 1000, including ADCs and DACs.
The price drops under 800 if you order... 100 modules

The software (called Monkey Software) is quite expensive: 2500
So this is really not meant for the end user: you are supposed to by a ton of modules and on instance of the software, and build/distribute your active speakers...
I have no idea if impulse generated by another software can be loaded in the HD2, but maybe the down sampling trick requires the original software?...

Quote:
The miniDSP DRC is $300 and it appears your impulse can be used.
Yes. They are going to release a new plugin to handle 8 channels with this device (in fact they are selling each par separatly, with the DSP module around $175, connected with I2S), but as they are sparing some power for additional biquads and are targeting a 96khz (!) sampling freq that only leave 512 taps per channel (which is really short at that freq...).
Ths plugin is not released yet and it seems they might add the option to freely distribute taps across channels...

By the way John, I have a question I wanted to ask you for some time, and this is the perfect opportunity: is a BR (Helmotz resonator) a phase linear thing? Or is there something special about the ringing?
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Old 26th December 2012, 02:45 AM   #54
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VSTconvolver plugin is free,fft partitioned multi convolution engine too.

FIR EQ/crossover +DRC+phase linearizaton pc based
Thierry, do you know of any plugin that does direct convolution?
I have played with SIR but found some annoying artifacts... (on specific test signals)
If the PC is powerful enough it looks like direct convolution is the way to go. I have no idea how much power it would require though...
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Old 26th December 2012, 02:54 AM   #55
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Thierry, do you know of any plugin that does direct convolution?
I have played with SIR but found some annoying artifacts... (on specific test signals)
If the PC is powerful enough it looks like direct convolution is the way to go. I have no idea how much power it would require though...
Please give test setup and examples of annoying artifacts.
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Old 26th December 2012, 03:02 AM   #56
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Andrew, it was on an older version of a test software developed by member jlo.
It was meant to compare phase distortion effects with/without a convolution (generated with rephase) on tests signals (sawtooth, dual tones, etc.).
The first version was using SIR and I could hear some distincs artifacts (hi tuned sounds, if my memory serves me well). jlo then implemented the convolver plugin instead or SIR and all was good.

I don't have the early version using sir anymore, but I can ask jlo if he still has it if you want.
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Old 26th December 2012, 03:37 AM   #57
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By the way John, I have a question I wanted to ask you for some time, and this is the perfect opportunity: is a BR (Helmotz resonator) a phase linear thing? Or is there something special about the ringing?
please read minimal phase and not linear phase, of course...
(too late to edit the original message)
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Old 26th December 2012, 03:50 AM   #58
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That's OK. I've worked extensively with extensively with Sourceforge convolver, and mostly use it single partition. Very modest PC can do easy 8ch 65k taps fs 48kHz.

Farina's convolution engine produces exceptional correlation with above, and have worked with 2^22 length test signals to push math noise hard. Modern FFT libraries are amazing.

Why direct convolution?

Regards,

Andrew
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Old 26th December 2012, 07:15 AM   #59
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Originally Posted by john k... View Post
So these high sampling rates twest820 was asking for really aren't all that useful. The impulse would (sampling rate)/6 taps long to have reasonable accuracy at 20 Hz. You are probably going to start having problems with round off errors etc.
Please refer to the scenario described in post 28; you seem to be confusing dipole equalization filters with DAC antialiasing filters.
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Old 26th December 2012, 10:22 AM   #60
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Originally Posted by thierry38efd View Post
VSTconvolver plugin is free,fft partitioned multi convolution engine too.

FIR EQ/crossover +DRC+phase linearizaton pc based
Yes, but I'll stick with the Bodzio UE as it is a complete, all in one package for speaker management including measurement, filter design and playback.
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