Article: Dirac Live 2 Digital Room Correction Software Walkthrough

[pga]

Recently hired Mitch to optimize my system.  Intelligently applied DSP is the most important change to my system since I started with this hobby in the late 1970s while studying electrical engineering in college.   Mitch ended up using Audiolense.   We’re on the second set of filters, trying to dial in the “perfect” timbre for my taste.  Over the years like most audiophiles I made many changes, most resulted in incremental Improvement, but this is the first true game changer in how my system sounds.   Real science, measurable results, very talented, easy to work with remotely.   What else can I say.  

[The Computer Audiophile]

2 minutes ago, pga said:

Recently hired Mitch to optimize my system.  Intelligently applied DSP is the most important change to my system since I started with this hobby in the late 1970s while studying electrical engineering in college.   Mitch ended up using Audiolense.   We’re on the second set of filters, trying to dial in the “perfect” timbre for my taste.  Over the years like most audiophiles I made many changes, most resulted in incremental Improvement, but this is the first true game changer in how my system sounds.   Real science, measurable results, very talented, easy to work with remotely.   What else can I say.  

Hey PGA, great to read about your experience with Mitch and the results. It mirrors my experience. DSP has come a very long way and in the right hands it’s amazing. 

[mitchco]

18 hours ago, R1200CL said:

Could one (Dirac) limit the frequency band below a certain frequency ? Like you concentrate the frequency taps in restricted area, and then achieve a more narrow frequency bin. 
 

I think no, cause this is about frequency resolution, so you can’t shrink somehow. 
 

Also some HW manufacturers is using 96 kHz, and then you actually need double the number  of taps in in order to achieve same resolution. Correct ?

 

What would be an acceptable frequency bin or resolution ?

I probably don’t ask the correct question, but I hope you somehow understand what I’m thinking about 😀

Like adjusting more taps to lover frequencies. And less to the higher ones. Don’t think this make sense. 

96000/65536 = 1.46 Hz. Would you like to see a lower number, or what is acceptable In your opinion ?

I notice Dirac now have a basic version below 500 Hz for 3.x, and then you pay extra in order to get access to adjust frequency above that. 
I still would think Dirac requires some sort of available processing power from the HW manufacturers. Unless Dirac supplies the board to the manufacturers. Do you happen to know anything about how this works ?

 

 

 

Hi @R1200CL Dirac is a bit different than other DSP software in that it uses a combination of IIR and FIR filters. This paper covers how it works, Controlling the impulse responses and the spatial variability in digital loudspeaker-room correction." Note Dirac does not have many user adjustable controls...

 

This short primer on FIR Filter for Audio Practitioners answers your questions on calculating the number of taps and frequency resolution. If you really want to get into it, then I suggest this accessible text on, 

"The Scientist and Engineer's Guide to Digital Signal Processing."

 

I say this as your note on more "filtering" down low and less up high is doable, but it involves more than just the number of taps... We get into Frequency Dependant Windowing and controlling how much amplitude and excessphase correction is applied at low frequencies versus high frequencies. This takes into account how much loudspeaker plus room gets corrected at low frequencies with how much direct sound is corrected at higher frequencies and by how much as it is all adjustable in other DSP software. It gets complicated quickly as there many variables to take into account, including why we hear what we hear in small room acoustics. My DSP book tries to explain this as simply as possible with examples.

 

Wrt to what DSP chips are used in what h/w devices, I could not say.

 

Happy listening!

[R1200CL]

Here is a good explanation Introduction to Filters: FIR versus IIR 
 

Audiolence and Acurate isn’t using IIR filters then I suppose. Only Dirac ?

[hulkss]

Hi Mitch,

 

I recently used the VST plug-in "Dirac Live 3 Multichannel" with "Jriver Media Center" as the host application. The output of Dirac goes into Jriver DSP where I have bass management, digital crossovers, and multi-subwoofer optimization filters (MSO software).

 

I did a  9 measurement cube with an Earthworks M30 mic (8 corners plus center), set target responses as needed, and generated a filter set.

 

This the BEST my system has ever sounded plus it's quick and easy (not counting the separate use of MSO and REW to generate my subwoofer line array filter set).

 

Dirac Live Bass Control for optimizing multiple subwoofers is in the works and may be able to replace my use of MSO. I'm a bit skeptical as MSO is truly amazing in what it can achieve.

 

Dirac Live Bass Control Illustration (just happens to be how my subs are arranged). No rear subs in my case.

 

[mitchco]

HI @hulkss Cool! Any photos of the setup to share? Or a graph or two of the result?

 

Cheers,

Mitch

[hulkss]

Hi Mitch,

Here's a couple pics of the room and my first quick try with Dirac playing and measuring through Jriver DSP.

I had to switch the surround channel assignments into and out of Dirac and adjust the LFE test signal output level -10db to get correct results.

 

 

[The Computer Audiophile]

5 minutes ago, hulkss said:

Hi Mitch,

Here's a couple pics of the room and my first quick try with Dirac playing and measuring through Jriver DSP.

I had to switch the surround channel assignments into and out of Dirac and adjust the LFE test signal output level -10db to get correct results.

 

 

Love it!

[hulkss]

For the ultimate in two channel music playback I use the vst plug-in DTS Neural Surround UpMix.

 

The wide sound stage and imaging is great for listening outside the small sweet spot of 2 channel stereo.

[mitchco]

@hulkss very cool man! Would love to hear your system! Very interesting about DTS Neural Surround UpMix, will have to look into that... Curious about what your JRiver DSP Studio looks like and the order of your plugins... How is the MSO filter added?

[hulkss]

Hi Mitch,

I have a 7-meter-wide subwoofer line array consisting of one central Infinite Baffle (IB) Subwoofer, flanked by four Epik Empire subwoofers, and two Klipschorn corner-horns. Fourteen 15-inch drivers in all, driven with 5 amplified input channels: one for the IB, one for each K-Horn, and two channels for the two Epik pairs. The corner horns play L & R  channel content above 80 Hz and are part of the subwoofer array below 80 Hz.

Here is the Jriver DSP Set-up (all 64 bit processing with 24 bit, 48 kHz signals):

DTS Neural UpMix is a VST3 Plug-in inside of DDMF Metaplugin64 v 3.4.3. That's what I could get to work properly.

Next Jriver PEQ2 swaps side and rear surrounds, then into the Dirac plugin.

I attached a list showing what makes up the somewhat confusing audio channels and then the Jriver DSP.

The last image shows the Robert Bristow-Johnson (RBJ) parametric equalizer “bi-quad” filters from MSO that are in the last image of Jriver Parametric Equalizer DSP.

 

As far as I know an unlimited number of filters can be entered into Jriver DSP.

 

[mitchco]

Wow @hulkss that is some engineered system you have there! Like I say, I would love to hear it!  14 x 15" woofers, that must be some slam!

 

Just in case you did not see it, JRiver 27 will have VST3 support: 

https://yabb.jriver.com/interact/index.php/topic,126706.0.html 

Still likely need the metaplugin...

 

Thanks for sharing!

[hulkss]

38 minutes ago, mitchco said:

Wow @hulkss that is some engineered system you have there! Like I say, I would love to hear it!  14 x 15" woofers, that must be some slam!

 

Just in case you did not see it, JRiver 27 will have VST3 support: 

https://yabb.jriver.com/interact/index.php/topic,126706.0.html 

Still likely need the metaplugin...

 

Thanks for sharing!

 

The software can be problematic. I loaded an update to Metaplugin a few months ago and it gave me trouble so I am holding at v3.4.3 for now. I'll try updating again when Jriver 27 is ready. Thanks for the VST3 heads up.

 

Sadly, it's a rare audio mix that has the dynamic range to sound truly live and use the full potential of this system.

[hulkss]

On 9/7/2020 at 12:16 PM, mitchco said:

@hulkssVery interesting about DTS Neural Surround UpMix, will have to look into that... 

 

Here is some info on Neural Surround UpMix. I think it provides the best sound available for home theater and I've tried several.

 

 

Neural Surround.pdf

[asdf1000]

On 4/17/2020 at 12:35 AM, mitchco said:

I don't know how Dirac is implemented in these h/w devices, but on a PC you typically use 65,536 taps per channel which gives full low frequency control. Remember the primary purpose of DRC is to correct the low frequencies below Schroeder. So my review of Dirac 2 is only in the context of using Dirac on a PC.

 

Hi @mitchco

 

From the quoted, are you saying that Dirac Live 2 on PC (that you used and reviewed) is using 65k taps per channel?

 

Since you gave Dirac Live 2 on PC a good review on its performance, including correcting low frequencies below Shroeder, then can we assume this PC version is using 65k taps per channel?

 

Thanks !

[mitchco]

@asdf1000No, what I am saying is that PC's can easily process 65,536 (or even  131,072) FIR filter taps. Whereas most h/w solutions are limited to 8096 taps or less per channel (typically 1024 or 2048 FIR filter taps).

In the case of Dirac, on the PC, we don't know how many filter taps are used as Dirac uses "mixed phase" filters which are a combination of IIR filters for low frequencies and FIR filters above a certain frequency. It is a black box and as mentioned in the article, you can read about Dirac's tech.

[asdf1000]

6 hours ago, mitchco said:

In the case of Dirac, on the PC, we don't know how many filter taps are used as Dirac uses "mixed phase" filters which are a combination of IIR filters for low frequencies and FIR filters above a certain frequency. It is a black box

 

Thanks @mitchco and all is noted.

 

I guess despite being a black box, from your detailed analysis and verification, it's doing a good enough job to be in the "state of the art" category with Audiolense and Acourate. So number of taps isn't worth (me) worrying about.

 

The Bass Control feature coming will be cool, to allow Dirac Live to handle DSP crossover to sub/s

 

[Ultrasonic]

On 4/14/2020 at 1:03 AM, mitchco said:

Dirac I believe is cut only filters,

 

For info. I believe Dirac Live actually applies boosts of up to 10 dB. I'm basing this on my experience of running DL on a miniDSP SHD, and using REW measurements to assess the filters applied. Specifically: making a measurement with a DL filter applied and one without, and then dividing the former by the latter to see the applied filter. It has also been observed by several miniDSP users that not allowing sufficient headroom for such boosts can lead to audible distortion, attributed to signal clipping in the digital domain. The 10 dB figure also tallies with information posted in the past by miniDSP staff.

 

It's possible that the DL behaviour is different when implemented on PC/Mac but my guess would be that the behaviour is the same.

 

@mitchco Thanks for taking the time to share your thoughts. I was interested to read your positive experiences of making measurements with furniture moved out of the way. This is not something I've tried but I will now 🙂.

[vavan]

On 12/12/2020 at 12:57 PM, Ultrasonic said:

I believe Dirac Live actually applies boosts of up to 10 dB

or even more. it reserved 12.5dB for me

 

On 12/12/2020 at 12:57 PM, Ultrasonic said:

It's possible that the DL behaviour is different when implemented on PC/Mac but my guess would be that the behaviour is the same

using vst version

[Ultrasonic]

9 hours ago, vavan said:

or even more. it reserved 12.5dB for me

 

I think the headroom to allow and the maximum boost applied at an individual frequency are slightly different things, principally because the phase changes introduced can also increase peak levels. On the other hand music signals are usually a complex mix of frequencies rather than a simple tone, so a 0 dBFS signal at the frequency of max boost would be very rare.

 

miniDSPs don't automatically 'reserve' any headroom by the way, so there is no equivalent I can give you to compare.

[mitchco]

Here is a loopback sweep through JRiver of Dirac's correction filter used in this article on top. On bottom is another DSP product using a FIR correction filter for the same speaker (both left channel). I drew a red line just above the FIR correction filter as I know that is 0 dBFS as I can inspect the FIR filter directly and measure it's peak amplitude in another application.

 

 

As I can't inspect the Dirac correction filter directly, or know what is going on in the DiracLiveProcessor (i.e. is it "just" a convolution engine or is there additional processing?) it is difficult to draw any real conclusions. The only conclusion I can draw is that the two filters are going to sound different. Note some other DRC/DSP software products provide the user the capability of adjusting how much correction is applied.

[Schlager]

Thanks for another good "walk through" of DCR software. Acourate, Audiolense and Dirac has been evaluated. May I suggest that you throw the freeware program DRC Designer into the mix? I know that the author of Acourate has been involved in the making of DRC Designer.  

http://www.alanjordan.org/DRCDesigner/DrcDesignerHelp.html

[mitchco]

Thanks @Schlagerfor your note. I should mentioned that Focus Fidelity Designer was also reviewed here at AS.

 

DRC Designer is used in conjunction with Denis Sbragion's DRC for creating room correction filters: http://drc-fir.sourceforge.net/doc/drc.html I have used this DSP software before and is very good!

 

There is a long thread on diyAudio that goes into it's usage of both DRC and DRC Designer for folks that want to roll up their sleeves and play with it: https://www.diyaudio.com/forums/full-range/275730-convolution-based-alternative-electrical-loudspeaker-correction-networks.html

 

I mention this as I don't have time for a formal review, but their is a lot of good information on the diyAudio thread.

[Schlager]

Thanks Mitchco for your reply. Good you can confirm that DRC Designer works well, now that you are very well advised in commercial products. I have used DRC a couple of years and have followed said thread and it works nicely with my DIY behemoth synergy horns. I didn't find the standard filters in DRC sufficient enough for my liking, but tweaking filters is pretty easy when using Alan Jordans GUI on top of DRC.