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Review and Measurements and miniDSP 2x4 HD DSP and DAC

tvih

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After numerous turns of events in the past few weeks, I now have one kit version incoming. Gonna have to fashion a case for it myself, but the cased version wasn't gonna be in stock any time soon at the only domestic place selling the thing for a reasonable price. I just hope the quality is enough.

On which note since it is a kit and thus not limited by the standard case I/O-wise I was considering maybe latter adding the i2s -> SPDIF output to allow using a better DAC for the main channels, while the other two could be directly connected to subwoofer(s).

There doesn't seem to be much in the way of ready-to-go solutions, and I definitely can't do my own custom PCBs or anything like that. I was looking at the second board linked by mdsimon2. I got a bit confused looking at the specs. The WM8055 talks about a single output channel. But can a single board still actually "pass through" a stereo signal from the 2x4 HD, or how exactly does it work? The digital outputs would seem somewhat awkward for mono and thus later combining into stereo. But if a single board gets the job done, how much work exactly is it to get it to "talk to" to the 2x4 HD, and what other parts - besides a connecting cable - does it require? I was a bit unclear if the reference to not being worth the time or cost to implement referred to also just one stereo pair output, or only to the trickier two pairs.

Overall seems weird that miniDSP themselves don't offer a "plug and play" solution for this. Or maybe they feel it would cannibalize the sales of their higher-priced products? Heck if I know.
 

mdsimon2

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I2S is not exactly easy for a typical consumer to troubleshoot. I feel like in the early days of miniDSP they were much more DIY friendly but have since shifted to more finished consumer products. They have warnings in the user manual and have repeated similar warnings on their forum for years. Based on all of this I don't think they will ever offer a plug and play solution.

1655147456913.png


The WM8805 data sheet is referring to a single SPDIF output which is a stereo output, so if you have one board you will be able to create a single stereo output.

The J7 pin header on the 2X4HD which contains CH 1/2 data (Pin 9), CH 3/4 data (pin 10) BLCK (pin 12), MCLK (pin 13) and ground (pin 14) is 2 mm pitch. I used a female to female 14 pin 2 mm pitch IDC ribbon cable and cut off one end and installed female contacts / housing for 2.54 mm pitch for the corresponding header I installed on the WM8805 board. The wiring is pretty self explanatory MCLK to MCLK, BCLK to BCLK, etc. If I was doing this as a permanent setup I would not install any headers on the WM8805 board and would instead directly solder to the WM8805 board. I would probably also just buy 14 pin 2 mm pitch housing and contacts rather than use a ribbon cable.

You will need to provide +5 VDC to the WM8805 board. The 2X4HD power supply runs at +12 VDC so that doesn't work without modification. Not sure the best way to power the WM8805 board to be honest, whether you want it on a completely separate supply from the 2X4HD or whether you want to tap from somewhere on the 2X4HD board. When I used multiple WM8805 boards with a miniSHARC (which ran on +5 VDC) I just powered everything from the miniDSP SMPS and it worked great.

Overall it is not hard to wire up, just that if you have issues troubleshooting will be very difficult without a high speed scope. And when you are done you still need to DIY an enclosure and the solution is a bit hacky.

Michael
 

tvih

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Thanks for the info. So, basically just the signal wiring between the two and indeed the power (which I figured but neglected to mention). Is the power supposed to be via the pins as well or soldered to the whatsamacallits labeled J5 (as you can see I'm a total noob at this stuff)? I suppose technically a basic 5V mobile charger would be a sort of easy source for 5VDC, though I'm not familiar with soldering connectors (in this mobile charger case that'd be a USB connector I suppose, though I should probably have some extra 5V wall warts with the round DC plugs as well) onto PCBs if that's required in this case. I'm no good with any sort of precision soldering, pretty much the best I can normally do is soldering connectors onto battery/speed controller wires for my RC cars/planes. And they're definitely of the thicker variety!
 

tvih

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The 2x4 HD has been working for its purpose very nicely performance-wise. However, one unfortunate thing is not being able to set the volume independently for each input. The unit is between my AVR and the amp driving the main channels, with subwoofer also handled by the 2x4, and there's a MASSIVE difference in source volume between sound coming via the AVR as compared to a PC connected directly via USB to the 2x4 for stereo listening (to do away with the extra DAC-ADC cycle from the AVR and all that) despite the pre-out volume for the fronts being maxed from the AVR (+10 dB). On the other hand increasing the overall AVR volume to even out the difference compared to the USB would require a separate integrated amp for the rear channels so that they don't get too loud compared to fronts; they're already at -10 dB... a messy setup, I know. Ugh.

So as it is the direct USB signal has to be toned down a LOT compared to signals going via the AVR. It becomes extra problematic if I ever do get an actual power amp for the main channels, instead of the integrated I am using now. Accidentally blasting full volume with something like an NCore 252MP-based amp - which would be a realistic option at some point, unless Topping or someone comes up with something nice for the job in the meantime - could theoretically blow my (expensive!) speakers, which are only officially rated to 150-170W or something like that... to speak nothing of what would happen to my ears!

I know optimally the computer volume shouldn't be controlled by the Windows volume control, or even the audio player being used, but it seems kind of a must here, and even more so if I did in fact have a more powerful amp - but even that still leaves room for user error. The current amp used is only 2x40W at 8 ohm with no official spec for 4 ohm which is what my speakers are, which means that even if I did blast full volume at least the speakers should be fine (unless it becomes a truly catastrophic amp failure, I suppose). As is, though, the amp is set to a bit more than half volume on the pot since I seemed to get the least noise in the overall chain that way (as opposed to not having the +10 dB pre-out boost and instead increasing the volume from the integrated for example... though that would also make the source volume difference all the bigger!). No directly turning down a pure power amp though! My brain being the swiss cheese it is and given the resulting lack of proper mental function, the full volume incident would probably be a question of "when" rather than "if" it would happen. Even setting a pre-amp dampening for the 2x4 output device in Equalizer APO on the PC would be far from foolproof since it stops working with every damn driver upgrade and such (just today noticed that it had been uninstalled from ALL audio devices for mysterious reasons).

Of course the safest option other than getting the separate rear channel amp with its own volume control would be to not use the USB connection directly, but given it's hardly a state of the art AVR and 12 years old to boot it's not exactly the grand champion of clean signals for critical listening, even if it still should generally be drowned out by the noise floor of the room. Plus especially in hot summer days it'd be nice to not need to have the AVR powered on just for music. Gets too damn hot in the apartment as it is!
 

Plcamp

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there's a MASSIVE difference in source volume between sound coming via the AVR as compared to a PC connected directly
Yes, AVR’s can have 0 db output level lower than the 2V you get from a digital input.

Your AVR might have ability to increase output voltage such that it is outputting 2V @ 0 db.

Alternately you could save one of the four stored setups to boost the incoming AVR signal inside the 2x4 hd.
 

tvih

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Yes, AVR’s can have 0 db output level lower than the 2V you get from a digital input.

Your AVR might have ability to increase output voltage such that it is outputting 2V @ 0 db.

Alternately you could save one of the four stored setups to boost the incoming AVR signal inside the 2x4 hd.
Well, it would probably reach 2V or at least closer to it if the overall AVR volume was higher - but as said that would require the separate amp for the rears as well to turn them down.

As far as boosting the AVR signal inside the 2x4... well, preset-wise it would have to be done in the output settings. Might lead to clipping, though? Plus it's limited to +12 dB, AND it'd still retain the possibility of making an user error since it would require remembering to change the preset manually.

Speaking of the NCore amps though, I guess the 122MP-based one that does 2x125W instead of 2x250W should still sound as good and not blow the speakers, but still would murder my poor ears :p
 

tvih

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I made an interesting observation. It seems that if you have set the USB volume of the 2x4 HD in Windows to a specific setting like 10, and then plug it to a Linux machine, the "100%" volume on Linux is in fact that 10% you had in Windows. Curious. Unfortunately not really a long-term safeguard regardless.
 

tiramisu

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I know most everyone here is focused on the minidsp hd as a room correction device but I find myself thinking it would make a very nice insert in the recording chain for sound staging and parametric eq. Is there something I am missing?
 

Piere

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What is missing are proper handles for control. You only have a RC or need to use a computer dedicated to it. Not very handy in a real time recording or ediing situation. The thing is more intended as a black box once proper adjusted.
 

JSmith

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New measurements on the APx555 c/o Prof. @WolfX-700;

Analogue in;

AnalogDashboard.jpg


USB;

Dashboard-2.jpg



... conclusions;
Summary: How to say, the performance is really average (even I want to say poor). But if you consider the application scenarios and functions of this thing (this machine is used as a digital crossover, EQ, etc.), can it be said that there is nothing wrong at this price? But if you really use it, I don't recommend using an external DAC + analog input. Adding a DAC in front of this product is not very useful (old-fashioned analog audio sources such as LP and tape are fine). It is better to output digital audio directly with the built-in DAC.


JSmith
 

Willem

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It would be nice to have something similar that measures a bit better. Anyway, when I have time, my plan is to implement dsp equalization of just my subwoofers using MSO. For that, it should be fine. My DAC is an RME ADI-2 DAC, so I would only use the minidsp unit on one of the two analogue outputs (the rca one for the subwoofers, the other one would go straight to the power amplifier for the main speakers), and hence only have the degradation from the minidsp where it would be least audible, i.e. at the lowest frequencies.
But please, RME, could we pleasae have such functionality built into a future incarnation of the ADI-2?
 

Piere

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I guess this is with the recently used TI codec chip instead of the previous used AKM codec?
 

tvih

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New measurements on the APx555 c/o Prof. @WolfX-700;
Nice to see directly comparable measurements, though I gathered from amirm's later comments that SINAD was indeed in the ~90 range.

It would be nice to have something similar that measures a bit better. Anyway, when I have time, my plan is to implement dsp equalization of just my subwoofers using MSO. For that, it should be fine. My DAC is an RME ADI-2 DAC, so I would only use the minidsp unit on one of the two analogue outputs (the rca one for the subwoofers, the other one would go straight to the power amplifier for the main speakers), and hence only have the degradation from the minidsp where it would be least audible, i.e. at the lowest frequencies.
But please, RME, could we pleasae have such functionality built into a future incarnation of the ADI-2?
Well, the miniDSP Flex would seem to be exactly what you're looking for then? It's cheaper than the RME but measures essentially the same (SINAD 114 dB for the DAC) while having the same DSP functionality as the 2x4 HD. It took me a while to decide whether to try and save up for the Flex or make do with the 2x4 HD, but luckily for my use the latter seems to be good enough based on the last couple of weeks, and EQ:ing the main channels is certainly worth it too - especially since properly integrating the subwoofer(s) requires a high pass filter for the mains anyway. Certainly the 2x4 HD still measures much better than my amp does (based on the amp's official spec) and any noise/distortion is easily hidden by the ambient noise in the room.
 

Plcamp

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hence only have the degradation from the minidsp where it would be least audible, i.e. at the lowest frequencies.
Yes indeed.

Begs a question I have difficulty getting an answer to…

If I restrict the discussion to 300 hz and lower, what is the SINAD level that achieves ‘transparency’? I understand the -115db for the full range, but everyone acknowledges low frequency distortion is harder to detect.

Is minidsp2x4HD ‘transparent’ as a bass management device?
 

MCH

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. My DAC is an RME ADI-2 DAC, so I would only use the minidsp unit on one of the two analogue outputs (the rca one for the subwoofers, the other one would go straight to the power amplifier for the main speakers), and hence only have the degradation from the minidsp where it would be least audible, i.e. at the lowest frequencies.
Are you sure that is possible?

On a different subject, i learned here a couple of weeks ago that the 2x4HD can also output digitally through usb, so it is possible to skip its dac.
 

Sokel

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It seems that a good dac is a waste in front of that.So there's no much choises to maintain the performance of the good dacs.
 

Piere

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Are you sure that is possible?

On a different subject, i learned here a couple of weeks ago that the 2x4HD can also output digitally through usb, so it is possible to skip its dac.

True, but only with the control panel on the PC you can return the digital output back to the PC through USB. But as far as I know you cannot hook up your own USB DAC.
 

MCH

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True, but only with the control panel on the PC you can return the digital output back to the PC through USB. But as far as I know you cannot hook up your own USB DAC.
I am about to try with a raspberry pi using the minidsp as capture device in camilladsp and outputting to a usb dac. Cannot confirm yet if it works, but was told it does (camilladsp tutorial thread).
(The final purpose for me is to apply dirac live to the incoming signal)
 

Piere

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There is a utullity around called "Audio Wire" It makes it possible to route audio streams between different applications on the same PC. Maybe it can pick-up the ASIO input channels of the Mini DSP and route is to another USB device. Here output of de MiniDSP is ASIO input to the PC.
 

Piere

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Here a multi tone result of a 24db/oct X-over at 500 Hz. USB-out --> Shark DSP X-over --> USB in return.

X-Over MiniDSP.png



Blue = lo-pass, yellow = high pass Apart from some rounding noise, no distortion artefacts. Accuracy is way beyond the capabilities of whatever DAC in the world can accomplish. At least with this DSP.
 
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