Article: Dirac Live 2 Digital Room Correction Software Walkthrough

[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!

[mitchco]

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

 

Cheers,

Mitch

[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?

[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!

[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.

[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.

[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.