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**miniDSP DDRC-88A Official Thread**8-channel AI/AO Dirac Live in a box

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#1 · (Edited)
Guys,

This is a dedicated thread on the MiniDSP product called DDRC-88A home theater in a box for those who are interested in Dirac Live Room Equalization solution. Only applicable with existing pre/pro/receivers that have an 8-channel analogue output to separate amps.

What is Dirac Live?
Dirac Live digital room correction technology optimizes the sound system both in terms of it's impulse response as well as the magnitude frequency response. Dirac accomplishes room correction through a technique called mixed phase. I.e. it is not IIR nor FIR, but something in between.
A technical write-up on Dirac Live by Mathias Johansson from Dirac's website is here: http://www.dirac.se/media/12044/on_room_correction.pdf

Details of the DDRC-88A are available here: http://www.minidsp.com/products/dirac-series/ddrc-88a

Wiring diagram hookup for the DDRC-88A:


Owner's manual is available.


Cost is under a grand USD - not including shipping.
  • For European AVS members, contact Homestudio with details provided by Keith Barnes in post number 522.
  • For UK AVS members, contact Kalibrate with details provided by Keith Barnes in post number 593.
  • The rest of the world will have to order from MiniDSP based in Hong Kong.

Again this is an external box solution for:
  1. those who have external amps to drive speakers; or
  2. those who have active speakers.
If you have a receiver with internal amps, sorry it's not going to help much.


The DDRC-88A has both balanced and un-balanced inputs via Phoenix terminal blocks. A solution for those with XLR pre-outs has been given by miniDSP in their forum thread post number 17019. MiniDSP recommends to:
  • buy a short XLR patch cable;
  • Cut it in the middle;
  • Use the XLR male to bare stripped wire for the DDRC OUT. You just "screw" the bare stripped wire to the pluggin phoenix connector we provide in the package (see user manual); and
  • Use the XLR female to bare stripped wire for the DDRC IN.
AVS member Jerry has provided step-by-step details for XLR cable connection in post number 729. Post up-dated to include heat-shrink for a more professional looking finish. Thanks Jerry!


Analogue input and output connection details.
  1. MiniDSP has confirmed that it's possible to have a mixture of balanced and unbalanced signals. One has to take care of the gain structure - see 2nd post for additional information.
  2. On the analogue input side; use either the balanced or the unbalanced connection - not both on a per channel input basis.
  3. It is also possible to have unbalanced input and balanced output or the other way around.
  4. On the output side, both the the balanced and unbalanced terminals are active; i.e. 'hot'. So both can be used at the same time.


Features:
  • Bypass of the DDRC-88A is available. Good for those who would like to compare their current flavor of room correction such as Audyssey, ARC, YPAO, MACC, AccuEQ, PEQ, etc. vs. Dirac Live. Note when Dirac Live is ON, the REQ within the pre/pro/receiver needs to be disabled with distances/levels set to zero. See Markus post number 611 for details.
  • Correction is adjustable for start and end frequency as well as tilting to a custom house curve. I.e. One can start from 20Hz up to 1kHz with a 10dB tilt and no correction below 20Hz or above 1kHz.
  • Can store up to 4 presets of adjustable room curves.:) Dirac Live has single seat positioning (often referred to as the money seat) or a wider sofa seating positioning measurement options. The single and sofa seat + 2 more can be saved into the presets. This would allow some flexibility in tuning the sound depending on listening situation. I.e. having family/friends over vs. critical listening by yourself. Note that an unlimited number of projects can be saved on the PC for loading into anyone of the presets.
  • Can do multi-zones. I.e. Up to four 2-channel stereo systems in the home, see post number 4 for additional details.

Current issues:
  1. Has a maximum of 7.1 channels.
  2. If you have height/wides/ceiling speakers (Dolby Atmos, Auro3D, DTS:X), you may want to consider an additional DDRC-88A solution to go beyond 8 channels. (Edit: AVS members westmd and Keith Barnes have successfully implemented a dual DDRC-88A setup. westmd in post number 4,900 and Keith Barnes in post number 8,675 with the tutorial in post number 8,683.)
  3. Sampling resolution is capped at 48kHz, might be a disappointment for those with multi-channel hi-rez files. I.e. 192kHz/24bit.
  4. Have to use MiniDSP's microphone for in room acoustical measurement with Dirac. Model number UMIK-1. Post number 18,754 in miniDSP forum explains the reasons for this.
  5. No remote trigger to start or IR code for ON/OFF operation. There could be a potential issue when the unit losses power - may cause a thump to the downstream speaker. Suggested to leave the unit on all the time and this may not please some.

Trouble shooting:
  • If the front light is OFF and the switch mode power adapter is ON (i.e. showing a green light. Edit: Keith Barnes advised that not all units power adapter have a light to indicate it is powered ON in post number 8,937) most likely the internal fuse needs replacing. Specs for the fuse is 2Amp 250v 20mm x 5mm Slow Blow. Revised fuse rating by miniDSP as advised by Markus in post number 9,186.
 
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#12,961 ·
worst case signal is a coherent signal (e.g. a sinewave) peaking at 0dBFS on every channel, to sum them so the output still peaks at 0dBFS means reducing the LFE at 10.2dB and the mains by 20.2dB before summation.


send such a sine wave into your system, feed the output back into a soundcard (or oscilloscope) and look at the signal to see if it's still a perfect sine wave
Unfortunately, I don't have an oscilloscope to measure the output, Matt. So this is just another thing to worry about while flying in the blind. I still don't understand why MiniDSP doesn't mention this in their otherwise excellent user guide. And, of course, there is always the question whether at lower listening levels this ever really becomes an issue.

Edit: I don't see any mention in Markus' recommendation to reduce the mains by 20.2dB. More confusion.
 
#12,962 ·
Unfortunately, I don't have an oscilloscope to measure the output, Matt. So this is just another thing to worry about while flying in the blind. I still don't understand why MiniDSP doesn't mention this in their otherwise excellent user guide. And, of course, there is always the question whether at lower listening levels this ever really becomes an issue.

Edit: I don't see any mention in Markus' recommendation to reduce the mains by 20.2dB. More confusion.
the extra 10dB on the mains is dealing with the 10dB extra on the LFE

http://www.avsforum.com/forum/91-au...lu-ray-players-technical-discussion-only.html is one thread that explains what is going on (to save me from typing it out :) )

you don't need a scope though, just a line input on your soundcard is sufficient if you did want to measure this
 
#12,963 ·
Everybody should do that in order not to overdrive the unit. For 7 channels you would need to reduce each channel by 10.2dB.
worst case signal is a coherent signal (e.g. a sinewave) peaking at 0dBFS on every channel, to sum them so the output still peaks at 0dBFS means reducing the LFE at 10.2dB and the mains by 20.2dB before summation.
OK, I tried configuring bass management with the -10.2dB setting as recommended by Markus. Of course, this lowers overall output levels by 10dB as well, from ~74dB to ~64dB. So how do I recover this 10dB, raise the MV by 10dB?

Unless I am sure that I have a clipping problem at the levels I normally run, this is not a desirable solution for me.
 
#12,964 ·
you don't need a scope though, just a line input on your soundcard is sufficient if you did want to measure this
I started browsing the thread you referenced. It's a bit of a slog, but thanks for pointing me in that direction. From my perspective, there are a lot of "unknown unknowns" in my personal knowledgebase.

I searched for "inexpensive scope", but they are pretty pricey. I don't have a soundcard--just a laptop with HDMI running REW. So not sure how to measure at this time.
 
#12,965 ·
OK, I tried configuring bass management with the -10.2dB setting as recommended by Markus. Of course, this lowers overall output levels by 10dB as well, from ~74dB to ~64dB. So how do I recover this 10dB, raise the MV by 10dB?

Unless I am sure that I have a clipping problem at the levels I normally run, this is not a desirable solution for me.
I don't know how the bass management in the 88a is configured but if you've been doing it without any attenuation, before the channels are summed, at all then you will definitely be clipping digitally on pretty much all known movie content at various points during every scene.

There are 2 main options to recover the gain, one is in an analogue stage (e.g. by adjusting the input sensitivity on a downstream) amplifier and another is running the output stage from the dsp at a high level. For example, say you were running with 0dBFS = 2Vrms out, if you change that to 8Vrms you just added ~12dB which is more than the -10dB you lost.
 
#12,966 ·
I don't know how the bass management in the 88a is configured but if you've been doing it without any attenuation, before the channels are summed, at all then you will definitely be clipping digitally on pretty much all known movie content at various points during every scene.

There are 2 main options to recover the gain, one is in an analogue stage (e.g. by adjusting the input sensitivity on a downstream) amplifier and another is running the output stage from the dsp at a high level. For example, say you were running with 0dBFS = 2Vrms out, if you change that to 8Vrms you just added ~12dB which is more than the -10dB you lost.
Of the recovery options you mention, my current downstream amp has no sensitivity adjustments, so that isn't an option. On the 88A, the output voltage is configurable 4v or 8v. Several months ago, I reduced the output to 4v to see if I could quiet a very slight hiss noise, but it did not make any difference at all. Of course, I lost 6dB of output, which is why I am reluctant to lose even more output. So, I guess the easiest option would be to revert to the 8v output and live with whatever are the resulting output levels by raising the MV.

One last (two-part) question, since you have been so helpful--without a way to measure clipping in the output, is there a compromise other than reducing the redirected bass by the full 10.2dB? Or am I better off simply setting it to -10.2dB to be completely safe? And should I update my 88A bass management guide to recommend the -10.2dB recommendation to everyone?

I am stull confused why this has not been discussed in this thread before--the bass management plug-in has been available for quite some time. :confused:
 
#12,968 ·
One last (two-part) question, since you have been so helpful--without a way to measure clipping in the output, is there a compromise other than reducing the redirected bass by the full 10.2dB? Or am I better off simply setting it to -10.2dB to be completely safe? And should I update my 88A bass management guide to recommend the -10.2dB recommendation to everyone?
10.2 is the absolute worst case, I don't think there is any real content in existence that would require that much attenuation. ~8-8.5 is probably sufficient for real world content.

I can't comment on the minidsp though, it depends how their code handles this internally. It seems odd, if it is an issue with their software, that their own guide (https://www.minidsp.com/applications/home-theater-tuning/bass-management-with-ddrc-88bm#appendix-b) doesn't mention this at all.
 
#12,969 · (Edited)
10.2 is the absolute worst case, I don't think there is any real content in existence that would require that much attenuation. ~8-8.5 is probably sufficient for real world content.

I can't comment on the minidsp though, it depends how their code handles this internally. It seems odd, if it is an issue with their software, that their own guide (https://www.minidsp.com/applications/home-theater-tuning/bass-management-with-ddrc-88bm#appendix-b) doesn't mention this at all.
The fact that the guide section that you reference specifically states "Check also that the mix levels are all set to 0 dB" is peculiar, and seems to be in direct contradiction to @markus767's recommendation. Perhaps I will ask for clarification on the MiniDSP web site. Until then, I don't think I will make any changes.
 
#12,970 ·
The fact that the guide section that you reference specifically states "Check also that the mix levels are all set to 0 dB" is peculiar, and seems to be in direct contradiction to @markus767's recommendation. Perhaps I will ask for clarification on the MiniDSP web site. Until then, I don't think I will make any changes.
Discussion thread opened on the MiniDSP forum:

https://www.minidsp.com/forum/dirac-series-support/13185-correct-setting-for-lfe-mix-levels#31489
 
#12,971 ·
Could I get some help please? I recently had some work done at my house, all my A/V stuff was disconnect and power supply was removed from unit and was not marked. I have quite a few DC PS around and uncertain which one belong to the 88A. I think I found it, but not completely sure, but the output is 12VDC 3.34A, 40W Max made by Mean Well Enterprises. Could someone please confirm this for me? Or could you take picture of the 88A's PS? Thanks a bunch!!
 
#12,972 ·
Could I get some help please? I recently had some work done at my house, all my A/V stuff was disconnect and power supply was removed from unit and was not marked. I have quite a few DC PS around and uncertain which one belong to the 88A. I think I found it, but not completely sure, but the output is 12VDC 3.34A, 40W Max made by Mean Well Enterprises. Could someone please confirm this for me? Or could you take picture of the 88A's PS? Thanks a bunch!!
Here is the info:
LI SHIN INTERNATIONAL ENTERPRISE CORP
AC ADAPTER
MODEL: LSE9901B1260
INPUT: 100-240V 50/60Hz 1.5A
OUTPUT: 12V 5A 60W MAX
 
#12,974 ·
Sorry if this question has been answered already -- does the bass management plugin offer any possible benefits if I already have a miniDSP 2x4 to combine my subs? I'm working with 7 speakers and 2 subwoofers.
 
#12,976 ·
MiniDSP Support, as well as John Reekie, have posted responses in the MiniDSP Forum thread.
minidsp support haven't answered the question. What you're asking is not an installation specific question, it's a simple question of how they have implemented their plugin (i.e. do they attenuate each channel before summation or do they expect you to have done that already? if the former, how much do they attenuate each channel by?)
 
#12,977 ·
Sorry if this has been asked before but I couldn't find it in a quick search.

Are the balanced and unbalanced inputs/outputs simultaneously active?
 
#12,979 ·
minidsp support haven't answered the question. What you're asking is not an installation specific question, it's a simple question of how they have implemented their plugin (i.e. do they attenuate each channel before summation or do they expect you to have done that already? if the former, how much do they attenuate each channel by?)
Well, I did not state the question in exactly those words, which is probably why you don't see the answer you are looking for. However, I did receive two bits of information. First, to make sure that the input voltages from the AVR are not exceeding the rated input of the 88A, which I had already done. And second, that the reading on the RMS output meters is useful to assess whether over-driving is occurring, which I have also done. So I am comfortable that my settings are good enough.
 
#12,980 ·
Well, I did not state the question in exactly those words, which is probably why you don't see the answer you are looking for. However, I did receive two bits of information. First, to make sure that the input voltages from the AVR are not exceeding the rated input of the 88A, which I had already done. And second, that the reading on the RMS output meters is useful to assess whether over-driving is occurring, which I have also done. So I am comfortable that my settings are good enough.
If your last post on that thread is the test performed then you are missing the point, you can clip during bass management without a single individual channel clipping. The output meters won't help you here.

The last post from john.reekie is on the right track. If you want to test this then you need to use multiple input channels. Can you copy a channel in the minidsp plugin? If so, this will be an easy test to setup.
 
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