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TOPIC: miniSHARC with OpenDRC2x2 plug-in?

miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12097

  • anlin
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Hi

Is it possible to use the OpenDRC 2x2 plug-in to program miniSHARC boards?
My plan is to use three miniSHARC kits with AN-FP's to equalize 6 independent balanced analog channels,

Am I right in assuming the ready-built OpenDRC box is a miniSHARC kit in a box mated to a VOL-FP and either an AN-FP or a DI-FP?
I am asking because I have no need for the volume control and the enclosure of the OpenDRC device, but I would like to have the extra FIR taps available (6148/ch for OpenDRC2x2, 2048/ch for miniSHARC 4x8, if I'm not mistaken).

I'm terribly sorry if this has been answered before, my quick search turned up no definitive answer.

Cheers
Last Edit: 6 years 5 months ago by anlin.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12099

  • OllBoll
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Yes you can, at least I have done it =)

Currently I have a MiniSHARC and then a NanoDIGI to do the actual crossovers, for the exact same reasons you list. If they had a plugin with all taps on the input ( or implement per channel downsampling for the FIR ) I'd probably skip the NanoDigi but they don't yet and I want to get my project finished this year =)
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12103

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Thanks so much for your swift reply, OllBoll.

That sounds really promising. I'm assuming you are using the miniSHARC's SPDIF outputs to drive the nanoDIGI? Do you have any experience with the AN-FP ADC-DAC and how it might work with the 2x2 plug-in? The signal chain would look something like this:

[HT PREAMP]
||
|| ==(2x bal XLR)==> [AN-FP #1 (ADC)] ----> [miniSHARC #1 ] ----> [AN-FP #1 (DAC)] ==(2x bal XLR)==>[C+SW channels]
|| ==(2x bal XLR)==> [AN-FP #2 (ADC)] ----> [miniSHARC #2 ] ----> [AN-FP #2 (DAC)] ==(2x bal XLR)==>[L+R channels]
|| ==(2x bal XLR)==> [AN-FP #3 (ADC)] ----> [miniSHARC #3 ] ----> [AN-FP #3 (DAC)] ==(2x bal XLR)==>[LS+RS channels]

The goal of all of this is to get rid of a bunch of really nasty room modes that ruin the low end and the lower midrange of the system. The room modes are rather strong all the way up to 200hz, so raising the subwoofer's crossover point doesn't really do anything. The IIR only miniDSP 8x8 would of course be a more cost effective solution, but I really don't think the ~20 parametric filters per channel are enough to smooth out the low end, never mind the midrange.

I could always just buy 3 OpenDRC-ANs and be done with it, but they cost almost $100 more each, and I would end up with volume controls that I don't want and enclosures that I don't need (I need to have all three boards in a single rack mountable unit).

Any suggestions? Ideas?

Thanks
Last Edit: 6 years 5 months ago by anlin.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12106

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Yes, I'm using a Digi-FP on mine's SPDIF output to drive the NanoDIGI, the AN-FP should work the same.

20 PEQs are a lot, as in really a lot. If you need more than 20 then you are probably doing something wrong =) I'm using the MiniSHARC for phase correction only and then sending it forwards to my mid+tweets on the NanoDIGI and my subs through 2 digital hypex plate amps on the AES/EBU output.

Also, If you get the MiniSHARC then you should take advantage of the FIR to correct the phase. If you don't then it's not exactly a cost efficient solution.
Last Edit: 6 years 5 months ago by OllBoll.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12116

  • anlin
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Yeah, the advantages of FIR filtering (independent phase and amplitude correction) are of course a major reason why I'm considering getting the miniSHARCs instead of a miniDSP8x8. 20 PEQs are a lot, I agree, but shouldn't a 6k+ tap FIR filter afford even more "resolution" still in addition to all the other benefits of FIR?
Could you elaborate on what you mean by correcting the phase - the phase response of the system+room at listening position or the phase response of the speakers in near field?
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12138

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Fixing the phase of the speaker only, if I remember correctly fixing the response with FIR is more expensive than using IIR for frequency changes and then fix the phase afterwards with FIR. If you do it that way ( which is also how Bruno Putzeys who built the Grimm LS1 does it ) then you have enough taps to fix the low frequency roll off too and can make it completely linear phase.

If you want to do room correction then you most likely need a multisub setup since otherwise the variances in the room would probably be too big for global EQ to be viable. Also, room correction in the midrange is probably too high since it is most likely above the schroeder frequency unless you live in a tiny room =) Even if you had an infinite amount of PEQs there is only so much global EQ you can use to globally fix the response, if the response still changes in a big way when you move your ear say 10cm then more EQ isn't needed, and with 20 PEQs you have probably already hit that limit.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12140

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Thanks for the clarification. The idea of using IIR for shaping the amplitude response and fixing the phase with FIR sounds good, that is probably what I'll end up doing.

The speakers I have (Genelec 8050) should not need any EQ to counter LF roll off or flatten the (nearfield) FR. The frequency response in fact tilts up rather steeply due to boundary gain from the speakers being placed near the corners of the room. The speakers do have rudimentary FR controls to compensate for this, but all of the settings either end up being way too aggressive (resulting in no low end) or not steep enough (emphasized low end). This was actually yet another reason why I started looking for a DSP solution for the mains.

Multiple subwoofers are unfortunately not an option, I already have one that more than fulfils all my low frequency extension and SPL needs. I also don't think I could even fit another 8 cu.ft behemoth in my listening room without compromising seating or speaker placement. Fortunately there isn't too much variation between listening positions, so I am able to get a reasonably flat (+-3db) frequency response from 16 to 120hz with 6 PEQs.

What is your take on AcourateDRC and other "automatic" FIR calculators? It seems most of them attempt to equalize the response well beyond the Shcroedinger freq. with very high-Q corrections.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12142

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What is your take on AcourateDRC and other "automatic" FIR calculators? It seems most of them attempt to equalize the response well beyond the Schcroedinger freq. with very high-Q corrections.

Schroeder, not Schroedinger - duh!
Last Edit: 6 years 5 months ago by anlin.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12150

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Automatic could work, as manual could work. The devil is in the details, however. What you would apply is global EQ and for it to be a good idea you need the peak to be global off axis too. If you take the response at 0 degrees and fix it to perfectly flat then it's likely that you will make it worse at say 15-45 degrees instead which isn't a good trade. If we look at the dispersion for your speaker in the datasheet ( www.genelec.se/documents/datasheets/DS8050A.pdf ) we see that the response is quite uniform already. You could possibly fix the small ~ 1800 hz bump since it exists of axis too but I can't see many more anomalies to fix except from the gentle 10 khz bump.

You should be especially careful with high Q fixes, and especially high Q peaks which might be a better idea to ignore.

You can of course fix the phase since it uses analogue crossovers, and when I talked about low frequency roll off I talked about phase correction and not amplitude correction =) As it has analogue EQ for low frequency roll off you might as well use that.

Personally I've not yet used the automatic FIR calculators, I've only used rephase. The OpenDRC 2x2 while not weak isn't that powerfull so if you want to EQ down to 20 hz you probably want to look carefully to make sure that any ripples are small enough. Rephase lets you do that easily which is nice. It also lets you trade off how close the phase response should be in favour for less ripple by playing around with different windowing functions and such.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12152

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What you would apply is global EQ and for it to be a good idea you need the peak to be global off axis too. If you take the response at 0 degrees and fix it to perfectly flat then it's likely that you will make it worse at say 15-45 degrees instead which isn't a good trade.
Just to make sure, what exactly do you mean by global EQ? I'm planning to do all EQ on a per-channel basis due to the asymmetry of the listening environment (hence the 3 miniSHARCs for a total of 6 independent channels).
You could possibly fix the small ~ 1800 hz bump since it exists of axis too but I can't see many more anomalies to fix except from the gentle 10 khz bump.
The Genelecs are indeed quite flat in terms of frequency response, which is why I mostly intended to use the miniSHARC for room correction at lower frequencies (<200Hz). I'll look into flattening out the 1.8kHz and 10kHz peaks, but seeing how they are only ~2dB in magnitude, I'm doubtful there will be an audible improvement.
You should be especially careful with high Q fixes, and especially high Q peaks which might be a better idea to ignore.
My sentiments exactly. I asked because I found it curious that so many automatic EQ algorithms should suggest such high Q adjustments to the higher frequency range, something I've always thought was generally a bad idea.
You can of course fix the phase since it uses analogue crossovers, and when I talked about low frequency roll off I talked about phase correction and not amplitude correction =)
Correcting the phase response of the system is definitely of interest to me though I'll probably need some pointers when I get the equipment set up due to my woeful lack of experience in phase correction. :)

As it has analogue EQ for low frequency roll off you might as well use that.
As I mentioned in my earlier post, the speakers' built-in LF EQ did not result in a desirable low-end response. I'll probably use one IIR filter per channel to correct for boundary gain and a few more for taming room modes.

Personally I've not yet used the automatic FIR calculators, I've only used rephase. The OpenDRC 2x2 while not weak isn't that powerfull so if you want to EQ down to 20 hz you probably want to look carefully to make sure that any ripples are small enough. Rephase lets you do that easily which is nice. It also lets you trade off how close the phase response should be in favour for less ripple by playing around with different windowing functions and such.
I'll have to acquaint myself with rePhase when I get the chance. Only the LFE channel is going to need EQ below 20hz, as the mains drop off quite sharply below 40hz anyways.



One more question about the miniSHARC kit - does it come with a power supply (site says it does, datasheet has no mention of it)? If so, what voltage range does it support (I'm based in Europe so the mains voltage for us is 230V)? Also, what are the power requirements for a miniSHARC+AN-FP, and would the (possible) stock power supply be able to handle three in parallel? I'm looking to build a rack enclosure for the three units, and I would really like to have a single power cable going to the EQ unit rather than three.
Last Edit: 6 years 5 months ago by anlin.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12153

  • OllBoll
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With global EQ I mean on the whole speaker, you can't EQ just say the front of the speaker without impacting the off axis response which might have a different response. But as we have established the Genelecs are already good in this regard which you already know so you probably don't need to touch them above room frequency =)

Hmm, I just realized one thing: are all our 5 "smaller" speakers Genelecs? If so then you already have a multisub layout =) Run all of them down to say 40 hz or where the room starts to sum. Let the sub take care of everything below this and up to about 100-120 or something. Then think of each genelec as a 40 hz+ sub + full range above and use this method to play around with them in the bass seriousaudioblog.blogspot.se/2012/05/two...les-on-multiple.html but use them full range so over the schroeder frequency just don't use any EQ. But since you would then have 6 sources in the 40-120 region you might not even have to do that method but can try to just run all of them full range to start with, they might cancel all problems anyway since they are so many.

On the phase side then you could try to first correct the phase anechoically on each speaker and sub, I think you could do it by putting the mike close up to the speaker. Then just take a measurement, load it up into rephase and fiddle until you get it flat enough and repeat with all speakers. Since you have 5 of them it is possible that you won't have to use specific EQ in the sub regions on each speaker but can use all normally so you might be able to just repeat one FIR filter on all of them.
Last Edit: 6 years 5 months ago by OllBoll.
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miniSHARC with OpenDRC2x2 plug-in? 6 years 5 months ago #12154

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With global EQ I mean on the whole speaker, you can't EQ just say the front of the speaker without impacting the off axis response which might have a different response. But as we have established the Genelecs are already good in this regard which you already know so you probably don't need to touch them above room frequency =)
Thanks for clearing that up. You have been extremely helpful and I really appreciate the time you taken to help me with this project :)
Hmm, I just realized one thing: are all our 5 "smaller" speakers Genelecs? If so then you already have a multisub layout =) Run all of them down to say 40 hz or where the room starts to sum. Let the sub take care of everything below this and up to about 100-120 or something. Then think of each genelec as a 40 hz+ sub + full range above and use this method to play around with them in the bass seriousaudioblog.blogspot.se/2012/05/two...les-on-multiple.html but use them full range so over the schroeder frequency just don't use any EQ. But since you would then have 6 sources in the 40-120 region you might not even have to do that method but can try to just run all of them full range to start with, they might cancel all problems anyway since they are so many.
Yes, all 5 of the main channels are Genelec 8050s. Thanks for the link, I'll give it a read it later this evening. I'll probably create two configurations for the speaker/sub crossover: one for multichannel audio (eg. movies), where the main speakers are run full range and the sub's low pass is defeated, and one for other material where the speakers and sub are crossed over at 40Hz. Quick measurements I did when I first set up the system indicated that there are several bad room modes below 80hz present when all channels are run full range, so there is still need for some EQ. I'm currently stuck with a laptop with no line input, so I'm unable to post measurements for the time being (I do have a USB audio interface coming in the mail).
On the phase side then you could try to first correct the phase anechoically on each speaker and sub, I think you could do it by putting the mike close up to the speaker. Then just take a measurement, load it up into rephase and fiddle until you get it flat enough and repeat with all speakers. Since you have 5 of them it is possible that you won't have to use specific EQ in the sub regions on each speaker but can use all normally so you might be able to just repeat one FIR filter on all of them.
Thanks, that sounds easy enough. I'll give it a shot when I get the miniSHARCs set up.


Any information on the stock PSU? I'd also love to know the power requirements for the base board + AN-FP.
Last Edit: 6 years 5 months ago by anlin.
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