2x4 minidsp

[NickH]

Hello,

In my journey in the land of subwooferia I purchased a minidsp to use as an eq for my sub. The sub is in a sealed cabinet so it starts to roll off around 30hz. The unit is a dsp as I'm sure you've figured out. The company that makes it is called minidsp and so is there website. They have many different units with more ins and outs then mine. Mine is primarily made for 2 way crossover duty. You can purchase different plugins from the company though. They allow you to do different things with the dsp.


Anyway I decided to try and use it to biamp my speakers. I'll use at or around 800hz point. But I'll also be able to test different frequencies now.

I figured some of you may be interested in the results I get with it. So figured I start this here thread about it. I already have an issue with most digital devices in the signal path. I can't stand the hiss. I know that there's a few good ones out there that have remedied this. We will see if minidsp is one. Since my speakers are of pretty high efficiency, it will be pretty obvious if they have not.

Nick

[NickH]

Ok no more joking around. I got the unit up and running. There is hiss. But its pretty low and doesn't get any louder, didn't expect it to. My speakers are pretty efficient, about 101db watt meter on the woofers alone. On ones of lower eff I doubt you'd notice it.

As used as tool this thing is great. Change crossover frequencies and crossover type and order with ease. You have a parametric eq's at your disposal. Also delay and polarity switching.

I'm not going to say what I think of its sound quality yet. I want to spend more time with it. I've only spent half an hour of listening where I wasn't playing with the frequencies. Odd thing is I'm back to the same frequency as my passives were.

the other cool thing is it can be power via USB. Or there's a connection for dc. The thing is tinny. It will easily fit in your pocket.

All in all not bad for 100 bucks. It doesn't seem to sound al, that bad either. There I spilled the beans. I'll do more serious listening though and report back.

Nick

[ivica]

......
As used as tool this thing is great. Change crossover frequencies and crossover type and order with ease. You have a parametric eq's at your disposal. Also delay and polarity switching.

I'm not going to say what I think of its sound quality yet. I want to spend more time with it. I've only spent half an hour of listening where I wasn't playing with the frequencies. Odd thing is I'm back to the same frequency as my passives were.

..... I'll do more serious listening though and report back.

Nick

Hi Nick,

Nice to see somebody dealing with miniDSP crossover. As I have understood they apply so call 'bi-quad' IIR digital filters for making crossovers (using DSP). As known IIR filters have not constant group delay either in the pass-band or in stop-band, but there are some known possibilities that unwanted behavior (phase "distortion") of the IIR filters can be reduced to the acceptable values, by using more complicated (with more taps) 'ALL-PASS' filters. My question is :are such structures present in the miniDSP crossover?

Reagrds
Ivica

[NickH]

Hi Nick,

My question is :are such structures present in the miniDSP crossover?

Reagrds
Ivica


I have an extremely rudimentary knowledge of this but as far as I can tell, yes.


There is a basic and advances panel for setting the crossovers. The advance is biquad input panel. There also seems to be a feature for creating the program/ parameters or what ever it is you input there. As I mentioned I know virtually nothing about it.


This will have to change if it does what you say. Thanks for the heads up.

Oh Ivica, I finally got a measurement mic. I bought it with the minidsp. Im planning on trying to do some measurement soon. Ive been using rew as a rta.

Nick

Here you go: http://www.minidsp.com/applications/advanced-tools/advanced-biquad-programming

[grey]

Thanks for sharing Nick. When I was looking at the minidsp, I was planning on using it for subwoofer filtering/management only. The plan was to use a PLLXO for the high pass as I'm doing today.

Someone here recommended a DBX driverack to sort out a different, complex system. I compared the free software download for both side by side, I noticed something that the minidsp was not advertising. The driverack offered phase rotation as a direct setting. It's possible that I've just not found this setting with the minidsp. It does have a nice selection of filtering for each channel however.

I've theorized the implementation of "all pass" filters accomplishing the same as phase rotation with DSP. I found some discussion in the link below that looks promising, although a bit more complex.

http://www.diyaudio.com/forums/minidsp/174145-minidsp-linkwitz-orion-asp.html

[NickH]

There supposed to be a way to do it. But I just learned about this today. It will take me a bit before I attempt it. Ivica brought this to my attention a few posts down.

There's a big difference between a driverack and this. The cheapest driverack is around 300 bucks. This is 105.

I actually bought it for the same reason as you considered it for. But its pretty cool even if you just use it as a design tool for picking a crossover frequency. I spent a bit of time with different frequencies and xover types. Good new is I ended up in the same place as the passive I originally built.

Considering what it is and how it works, the possibilities are end,ess as to what it can do. Its what the programmers can write.

I only have the 2.1 cross over plugin. I'll probably get the 2 way.

At the moment I'm not going to give a opinion on how they sound. I need to spend more time listening before I pass judgement.

[NickH]

Ive been listening and palying with settings on the minidsp for a week now. Ive got it dialed in were everything sounds great. Though mycrossover frequency between the bass horns and the 2445's will be a bit controversial. Im using the minidsp and my crossover for a 2 way setup. Its crossed at 400hz with a 48db per octave linkwitz riley crossover. Now before anyone freaks out, its only being driven with a whopping 4 watts. Although I doubt it see's anything close to that.


But Im very happy with it. Im currently working on a cd compensation on the eq for the 2" drivers. This thing surprised me. I never thought I would be content with a digital device in the signal path. Especially a dsp. Now all I need is another 2x4 so I can go all the way to 3 way active.


Ive played every type of music I can think of through it. No anomalies can be heard. The highs are crystal clear and so is the bass. Mids are phenomenal.

Nick

[ivica]

Thanks for sharing Nick. When I was looking at the minidsp, I was planning on using it for subwoofer filtering/management only. The plan was to use a PLLXO for the high pass as I'm doing today.

Someone here recommended a DBX driverack to sort out a different, complex system. I compared the free software download for both side by side, I noticed something that the minidsp was not advertising. The driverack offered phase rotation as a direct setting. It's possible that I've just not found this setting with the minidsp. It does have a nice selection of filtering for each channel however.

I've theorized the implementation of "all pass" filters accomplishing the same as phase rotation with DSP. I found some discussion in the link below that looks promising, although a bit more complex.

http://www.diyaudio.com/forums/minidsp/174145-minidsp-linkwitz-orion-asp.html

Ho grey,


May be I am not right, but it seems to me that with 'miniDSP2x4' boards only, real group-delay compensation is not possible due not present larger number of FIR taps, but if 'miniSHARC' board is used too, then that would be promising solution. I think in such solution 'minDSP2x4' would be used mainly as A-to-D and D-to-A converters, and may be some time delays, and gain (sensitivity of the drivers compensation). May be our member POS ( http://www.audioheritage.org/vbulletin/member.php?8209-pos ) can help more.

Regards
Ivica

[NickH]

You over my pay grade at the moment. Im still reading up on the biquad filter options. But it will be a while before I even attempt it. I cant see how it wouldn't be phase coherent though. It would seem pointless to have options to invert the output signals. Which it does. Or am I interpreting something incorrectly.

Nick

[4313B]

I thought I would put this link in here since the title of the thread is 2x4 minidsp

http://www.linkwitzlab.com/LXmini/Introduction.htm

[Lee in Montreal]

I thought I would put this link in here since the title of the thread is 2x4 minidsp

http://www.linkwitzlab.com/LXmini/Introduction.htm

Hmmm... went to the link and searched for miniDSP info. Found none. Are you sure it is the right thread to post this link?

@ Nick. The hiss your hear is most likely a problem with gain. Maybe the output of your MiniDSP is not high enough.

[hjames]

Hmmm... went to the link and searched for miniDSP info.
Found none. Are you sure it is the right thread to post this link?


I thought I would put this link in here since the title of the thread is 2x4 minidsp
http://www.linkwitzlab.com/LXmini/Introduction.htm

Oh god 4313B is a spammer!
Posting links for some other speakerbrand here!

I think the desired link is
http://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4
No affiliation, I don't own one and have gotten no pay or gratuities from those folks.



Hello,

In my journey in the land of subwooferia I purchased a minidsp to use as an eq for my sub. The sub is in a sealed cabinet so it starts to roll off around 30hz. The unit is a dsp as I'm sure you've figured out. The company that makes it is called minidsp and so is there website. They have many different units with more ins and outs then mine. Mine is primarily made for 2 way crossover duty. You can purchase different plugins from the company though. They allow you to do different things with the dsp.
Nick

[Lee in Montreal]

Oh god 4313B is a spammer!
Posting links for some other speakerbrand here!

Ah, ah, ah. 4313B has been abducted by aliens, and while he was being probed, the aliens hacked his LH account ;-)

[hjames]

Ah, ah, ah. 4313B has been abducted by aliens, and while he was being probed,
the aliens hacked his LH account ;-)

Oh god, thats it!
the probes ... the huge manatee of it all!

Poor Gisgy

[pos]

Hmmm... went to the link and searched for miniDSP info. Found none. Are you sure it is the right thread to post this link?
I would suggest to reread the linked page (onwards) more carefully ;)

[pos]

http://www.minidsp.com/applications/powered-by-minidsp/linkwitz-lab-lxmini

[ivica]

I would suggest to reread the linked page (onwards) more carefully ;)

Hi POS,

Knowing You as DSP expert in design digital filters, do You have any experiments in order to phase linearized IIR filter by implementing cascade of IIR all-pass filters, such as explained in the:

"EFFICIENT GROUP DELAY EQUALIZATION OF DISCRETE-TIME IIR FILTERS" by M.F.Quélhas,A.Petraglia,M.R.Petraglia
http://www.eurasip.org/Proceedings/Eusipco/Eusipco2004/defevent/papers/cr1483.pdf

AN EFFICIENT METHOD OF GROUP DELAY EQUALIZATION FOR DIGITAL IIR FILTERS by Piotr Okoniewski, Jacek Piskorowski
http://www.degruyter.com/view/j/mms.2013.20.issue-3/mms-2013-0034/mms-2013-0034.xml

or something here:
http://www.nt.tuwien.ac.at/fileadmin/users/gerhard/diss_Lang.pdf


regards
ivica

[pos]

Hi Ivica
Well, I am no DSP expert.
Phase linearization using multiple all-pass filters is a proven technique that is for example used by PSI Audio down to the low midrange in their studio monitors, using only analog components (CPR (http://www.psiaudio.com/technology/cpr)).
Compared to FIR the implied delay will be the same for a given phase correction, but I suspect it will generate much more quantization noise (multiple recursive filters).
And of course a given target will be much more difficult to approach with this technique than with FIR.

[ivica]

Hi Ivica
Well, I am no DSP expert.
..............
Compared to FIR the implied delay will be the same for a given phase correction, but I suspect it will generate much more quantization noise (multiple recursive filters).

Hi POS,

I can agree with You that quantization noise can rise (multiple recursive filters) , but using today 32-bit floating-point DSP ( such as ADSP21469 ) I think that such noise 'contribution' would be under the expectable level ( of -100dB), so may be You can improve Your nice work about phase correction, allowing to use much less filter taps (not to mention down and up sampling etc).

Regards
Ivica

[pos]

That would be interesting to add such a feature in rePhase indeed, but I don't know if all targets could be reached close enough that way.
I have a mixed biquad/FIR mode in the work that could make use of this technique. I don't have a lot of time to work on this these days though... :(

Quantization noise with IIR filters is real though, and needs special care when EQ has to be applied down low.
For example miniDSP typically specializes some EQ banks for LF purpose, with better precision to reduce quantization noise.

Here is an example comparing the DCX2496, the openDRC using IIR EQ (first firmware), and the openDRC using FIR EQ, with the exact same minimum-phase EQ :
62581

Uppers traces (indistinguishable) are amplitude responses.
Lower traces are noise measurements (quantization noise from the EQ + noise floor of the measurement system and units at test)

As you can see the openDRC IIR implementation was lacking precision for LF. Now they have somewhat "fixed" the problem in the openDRC by increasing the precision of the first IIR EQs slots (so you have to make sure you use those first slots for LF purpose, and only use the remaining ones for >100Hz EQs...).

Unfortunately the noise floor of that measurement is too high to really show differences between the openDRC FIR and the DCX2496, but they are also real :
Using headphones one can clearly hear noise when the sweap passes through the EQ point, whereas the openDRC in FIR mode is totally silent.
This is easy to hear on a sweap, even if it is very low in level, because the noise is fullrange and there is no masking effect.
This would probably not be a problem with music signal, but adding multiple EQs (or all-passes) would increase the audibility...

[ivica]

That would be interesting to add such a feature in rePhase indeed, but I don't know if all targets could be reached close enough that way.
I have a mixed biquad/FIR mode in the work that could make use of this technique. I don't have a lot of time to work on this these days though... :(

Quantization noise with IIR filters is real though, and needs special care when EQ has to be applied down low.
For example miniDSP typically specializes some EQ banks for LF purpose, with better precision to reduce quantization noise.

Here is an example comparing the DCX2496, the openDRC using IIR EQ (first firmware), and the openDRC using FIR EQ, with the exact same minimum-phase EQ :
62581

Uppers traces (indistinguishable) are amplitude responses.
Lower traces are noise measurements (quantization noise from the EQ + noise floor of the measurement system and units at test)

As you can see the openDRC IIR implementation was lacking precision for LF. Now they have somewhat "fixed" the problem in the openDRC by increasing the precision of the first IIR EQs slots (so you have to make sure you use those first slots for LF purpose, and only use the remaining ones for >100Hz EQs...).

Unfortunately the noise floor of that measurement is too high to really show differences between the openDRC FIR and the DCX2496, but they are also real :
Using headphones one can clearly hear noise when the sweap passes through the EQ point, whereas the openDRC in FIR mode is totally silent.
This is easy to hear on a sweap, even if it is very low in level, because the noise is fullrange and there is no masking effect.
This would probably not be a problem with music signal, but adding multiple EQs (or all-passes) would increase the audibility...

Hi POS,

Thanks for the data about the noise level of EQ using DCX2496, OpenDRC FIR and openDRC IIR.
As I have expected DCX2496, using 32-bit floating point DSP ( ADSP21065 DSP engine) even using IIR EQ has almost the same noise level as openDRC FIR EQ ( fs~ 20Hz), even I would expect about 20dB better results for DCX2496 then presented, but may be there is some other source of the noise.

If I have understood correctly, on DCX2496 there is audible noise that can be heard using headphones, and while applying sinusoidal signal around 20Hz.
Does such noise start to reduce while reducing the depth of the applied notch around 20Hz (it would be expect-able to diminish with almost flat EQ applied)?
May be such nose can be reduced by applying a kind of dither applying to the feed-back path of the bi-quad EQ filter, if You decide to realize EQ IIR filter.

Any how, I believe that Your rePhase great work can be applied to the miniSharc DSP using IIR phase compensation in order to reduce number of the FIR taps, and computation power.

Reagrds
ivica

[pos]

I will try to redo some measurements with a better noise floor and different situations (varying Q, gain and frequency...) but I think my soundcard AD converter (and most probably analog stage) will be the limiting factor here.

I also have a EV DX46 crossover I could measure (48bit fixed), but the digital input does not work anymore (I have no idea why :()

[ivica]

I will try to redo some measurements with a better noise floor and different situations (varying Q, gain and frequency...) but I think my soundcard AD converter (and most probably analog stage) will be the limiting factor here.

I also have a EV DX46 crossover I could measure (48bit fixed), but the digital input does not work anymore (I have no idea why :()

HI POS,

Waiting to see the data...

Regards
ivica

[4313B]

I just thought it might be interesting to see what someone else is doing with the miniDSP.