RePhase + Minidsp = puzzled

[Paffi]

Hi there,

currently I´m completely puzzled when it comes to the different minidsp-devices.

I´m using two main speaker and a dba (consisting of 4 subs, maybe more in future). I´d like to experiment with phase linearizaton and rePhase. So which minidsp to choose?

According to this two application notes:
https://www.minidsp.com/applications/advanced-tools/rephase-fir-tool

Two way crossover

miniDSP is a leading manufacturer of Digital Audio Signal Processors for the HomeTheater, Hifi, headphone and Automotive market. Join our large community of Audiophiles, Engineers and DIYers using our innovative products.

www.minidsp.com

I would at least need to different minidsp devices:

- one for crossover (minidsp 2x4 hd https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4-hd or minidsp flex https://www.minidsp.com/products/minidsp-in-a-box/flex)
- one for phase linearization of the whole system (minidsp Flex eight https://www.minidsp.com/products/minidsp-in-a-box/minidsp-flex-eight or OpenDRC https://www.minidsp.com/products/opendrc-series/opendrc-di)

Am I right, that there is no minidsp that can do both? I´m wondering why the flex eight can´t do the linear phase crossover but the phase linearization of the whole system.

So in my case I would connect an minidsp flex to the digital out of the OpenDRC. At the minidsp flex I connect the 4 Subs+Mains, doing the alignment of the subs and crossover of the mains (here the flex eight would be better due to 8 outputs, but according to the application notes, it should be the regular flex). When it´s done, I´m doing the phase linearization of the whole system at the level of OpenDRC.

Looks pretty complicated - is there another solution? Looking at the EOL-products, the OpenDRC-DA8 may have worked for that https://www.minidsp.com/images/documents/Product Brief-OpenDRC-DA8.pdf

Best regards,

Paul

 

[mdsimon2]

Am I right, that there is no minidsp that can do both? I´m wondering why the flex eight can´t do the linear phase crossover but the phase linearization of the whole system.

So in my case I would connect an minidsp flex to the digital out of the OpenDRC. At the minidsp flex I connect the 4 Subs+Mains, doing the alignment of the subs and crossover of the mains (here the flex eight would be better due to 8 outputs, but according to the application notes, it should be the regular flex). When it´s done, I´m doing the phase linearization of the whole system at the level of OpenDRC.

An OpenDRC is probably the best platform that miniDSP has for FIR filters, it can run at 48 kHz which gives it more FIR taps than the other platforms which run at 96 kHz. You can also use it as an 8 channel I2S output device if you use the miniSHARC plugin -> https://www.minidsp.com/products/plugins/minisharc-opendrc-plug-ins/minisharc-4x8-plug-in-detail. Of course, this requires an 8 channel I2S output DAC.

Using inverse all pass filters on an upstream OpenDRC-DI is a viable method to linearize crossover phase, see here for more discussion -> https://www.audiosciencereview.com/...-through-the-bass-roll-off.53966/post-1963794

If you go with the OpenDRC-DI + Flex option, I think you will want to use the Flex 8 instead of the normal Flex as the normal Flex does not have info outputs.

All that being said, I think you will find the FIR capabilities on miniDSP products limiting. See my signature for a tutorial on how to implement CamillaDSP on a raspberry pi with a multichannel DAC. This will give you essentially unlimited FIR taps.

Good luck!

Michael

 

[terryforsythe]

I would at least need to different minidsp devices:

No. The Flex Eight alone should be adequate. See the following Application Note for the Flex Eight: https://www.minidsp.com/applications/digital-crossovers/active-speakers-dirac-live

As Michael stated, CamillaDSP is another option, and Michael has a great tutorial for implementing it on a Raspberry Pi: https://github.com/mdsimon2/RPi-CamillaDSP

I have a miniDSP Flex HTx (it does not have FIR, which the Flex Eight does) in one system and CamillaDSP in another.

The miniDSP probably is simpler to setup, but CamillaDSP probably is more powerful. Also, if you use CamillaDSP you may need some type of audio output device for the Raspberry Pi. Which type depends on what type of audio output you desire (e.g., digital or analog. If digital, coax or TosLink).

 

[Paffi]

Thank you both!

An OpenDRC is probably the best platform that miniDSP has for FIR filters, it can run at 48 kHz which gives it more FIR taps than the other platforms which run at 96 kHz. You can also use it as an 8 channel I2S output device if you use the miniSHARC plugin -> https://www.minidsp.com/products/plugins/minisharc-opendrc-plug-ins/minisharc-4x8-plug-in-detail. Of course, this requires an 8 channel I2S output DAC.

Good to know! So the OpenDRC-DI can be upgraded from two channel output to 8 channel output? So, combined with an adequate DAC, maybe I could also use it for the crossover (4 Subs + 2 Mains) and use it without an additional Flex?

If you go with the OpenDRC-DI + Flex option, I think you will want to use the Flex 8 instead of the normal Flex as the normal Flex does not have info outputs.

What do you mean with "info outputs"?
The minidsp applications notes are stating, that only the regular flex could be used for linear phase crossover and not the flex 8, which was one of my questions, because I don´t understand it. You think It will work to? Quoting from the application note, number 7b:

Add the crossover (linear phase)
(This section applies to the 2x4 HD and Flex without Dirac Live only. It does not apply to the DDRC-24, SHD Series, Flex with Dirac Live, Flex Eight or Flex HT.)

All that being said, I think you will find the FIR capabilities on miniDSP products limiting. See my signature for a tutorial on how to implement CamillaDSP on a raspberry pi with a multichannel DAC. This will give you essentially unlimited FIR taps.

Thank you! I was always afraid of using raspberry and fizzling with dyi builts, as I´m preffering "finished box" solutions. Maybe I´m wrong with that.

No. The Flex Eight alone should be adequate. See the following Application Note for the Flex Eight: https://www.minidsp.com/applications/digital-crossovers/active-speakers-dirac-live

But that´s with dirac? I don´t want to use dirac and otherwise the (above linked) application notes mentions only the regular flex or 2x4hd for linear phase crossover Maybe the application notes are missleading and I should ask the minidsp support.

 

[mdsimon2]

Good to know! So the OpenDRC-DI can be upgraded from two channel output to 8 channel output? So, combined with an adequate DAC, maybe I could also use it for the crossover (4 Subs + 2 Mains) and use it without an additional Flex?

Yes...but dealing with I2S is a pain and any effort will DIY, much more so than any raspberry pi solution.

What do you mean with "info outputs"?
The minidsp applications notes are stating, that only the regular flex could be used for linear phase crossover and not the flex 8, which was one of my questions, because I don´t understand it. You think It will work to? Quoting from the application note, number 7b:

Haha, that was an odd typo, I meant "enough", not "info".

The regular Flex has FIR taps allocated to each output channel, while the Flex 8 has taps allocated to each input channel. Therefore, only the Flex can apply linear phase crossovers.

However, with the Flex 8 you can achieve the same end result by applying normal minimum phase crossovers on the Flex 8 (which will result in all pass phase response) and using an inverse all pass FIR filter on the input channels to linearize the phase response. You can do this inverse all pass on the Flex 8, but you will probably find it does not have enough FIR tap, because the OpenDRC-DI can operate at 48 kHz it will be roughly 4X more effective than the Flex 8 in this regard. This is why I shared that link showing a comparison of typical linear phase filters and minimum phase filters + inverse all pass.

EDIT: Do you have a rough idea of what filters you want to apply (alignment, slope, frequency)? If we know that we can do some modeling in rePhase and see what you need in terms of taps.

Michael

 

[Paffi]

After a long time, I got response from the minidsp support, confirming it:

Thanks for your interest in our products and sorry for the delay in getting back to you

- You're indeed correct that we don't have a miniDSP with both FIR on crossovers + FIR on input to linearize the whole response I'm afraid.

- Even the OpenDRC-DA8 actually wouldn't be able to do both. IT would only do FIR on the output side.

- Have you built your multiway speakers before? It's quite a process on its own to get this working. WIth IIR + FIR ontop it's going to achieve some great results already. You could even use Dirac live to do this for you with the Flex HTx. In a method that will leads to best results..https://www.minidsp.com/products/ht-series/flex-htx and here: https://www.minidsp.com/applications/digital-crossovers/active-speakers-dirac-live

As Dirac is a no no for me, probably the Flex 8 would be the best fit, as @mdsimon2 suggested. Unfortunately, it has no balanced outputs, which I would prefer for the Mains. It´s so unnecessary hard to find an preamp which has it all - maybe I should forget about manual FIR filter and stay with IIR...

EDIT: Do you have a rough idea of what filters you want to apply (alignment, slope, frequency)? If we know that we can do some modeling in rePhase and see what you need in terms of taps.

Michael

Will be propably below Schröder (but maybe I want to experiment with higher frequencies later), so mainly room modes and crossovers to the subs (time / phase alignment) between 80 and 140hz. As it´s configured as kind of an DBA currently, I´m just curious if there´s something to improve and if I could "beat" the Antimode X2 manually (Which is really great).