Active Room Treatment (ART) by Dirac

[thcdru2k]

For bass, most AVRs sum low frequencies to mono below the crossover, which removes left/right spatial cues. ART doesn’t just do a simple mono sum, but it still prioritizes smoothness across speakers rather than preserving strict channel separation, whereas keeping channels discrete into DSP retains those spatial cues more effectively. There are tradeoffs between spatial consistency and channel-specific fidelity. For the majority of rooms and setups, spatial consistency is the better tradeoff, therefore approaches like ART tend to yield more reliable overall results.

 

[thcdru2k]

I’d recommend listening to “Opus” by Eric Prydz. I’ve heard it live where the bass clearly moves across the stage. A home system won’t replicate that scale, but it can still reproduce the sense of width and movement if the integration is right. I’d listen on good headphones first to understand the mix, then compare on your system.

 

[JRowland]

I’d recommend listening to “Opus” by Eric Prydz. I’ve heard it live where the bass clearly moves across the stage. A home system won’t replicate that scale, but it can still reproduce the sense of width and movement if the integration is right. I’d listen on good headphones first to understand the mix, then compare on your system.

There is a difference between directional bass and what @Oddball was asking about which is auditory envelopment just to be clear about what that whole Billie Eillish song thing is about. I’m way out of my lane but this describes more of the technical aspects if you scroll to Temporal Response. https://www.genelec.com/-/blog/how-to-analyse-frequency-and-temporal-responses

His second reply here explains the subjective part a little

Genelec GLM Review (Room EQ & Setup)

In a nutshell, since I do this for a living. You need EQ whether using one sub or multiple. Very difficult to get a flat response even with multiple subs. What you want is a response you can equalize, meaning no dips that can't be fixed with EQ. If you are mixing music for instance and you only...

www.audiosciencereview.com

 

[kifeep]

@OCA mentioned on another thread:

use heavy filter downsampling and multirate algorithms like ART does (uses 1024 tap filters of varying sample rates per speaker/sub)

Rather than hijack that thread, I thought I'd ask here if anyone can explain how multirate filters work and if/how that gets around the usual bucket size limitation of low-tap-count FIR filters?

 

[Keith_W]

@OCA mentioned on another thread:


Rather than hijack that thread, I thought I'd ask here if anyone can explain how multirate filters work and if/how that gets around the usual bucket size limitation of low-tap-count FIR filters?

Let's say you have 4096 taps at 96kHz. The bin size is Fs/n = 96000/4096 = 23.4Hz. In other words, you would be correcting in 23.4Hz chunks - clearly not enough resolution for bass correction.

Now suppose we divide the incoming signal into two. One for <200Hz, and another for >200Hz. We assign half the taps to each (2048). And while we are at it, let's drop the sample rate for the <200Hz part to 1kHz (still well above the Nyquist freq). Now the bin size is 1024/2048 = 0.5Hz.

Disclaimer: I have the paper for multirate filters, and I have tried to read it, but the maths went a little bit over my head. That's about what I understood from it. Maybe someone with more DSP expertise can come along and correct me if i'm wrong.

 

[Oddball]

On the D&M setup you can set the subs to "Directional Bass" but when I was having some problems getting ART to recognize my rear subs (I have 4, 2 in front and 2 rear) Dirac tech support said to set this in the non-directional setting. I still had problems after this so I ended up resetting my receiver and that fixed it but I didn't go back to see if the directional bass needs to be off to work, or if it matters in ART since it's doing the bass management. But I've also seen (I think Dirac mentions this) that if you want the bass to be more directional (stereo) you should group your subs with the speakers, meaning left sub with left speaker etc. I haven't had time to try this in my system but I can say that stereo subs do make a sometimes obvious difference in the reproduction of spaciousness on recordings that haven't summed the bass to mono. I would expect the same for multi channel recordings as well. I myself don't know how much "directionality" is affected with subs grouped together normally because I have't had time to try all this out. I listen to both multi channel and stereo recordings on my system. I haven't listened to the Billie Eilish recording mentioned in another reply but it's certainly helpful to have a recording that demonstrates the difference when you're experimenting. I'm also traveling but will spend some time on this when I get a chance.

ART will disregard directional bass setting on D&M bass management, as well as any other settings like crossovers. So that's not a way to go directional with ART.

The most directional 2.2 setup, as you say, would be to create profile/calibration with 4 groups. L, R, L sub and R sub (subs being right by L/R speakers). Then support L with L sub and R with right sub. This is pretty much guaranteed to provide you with maximum "spaciousness". However, as @thcdru2k noted, this is a trade off with the overall performance of traditional cross-support ART system - which I also noted in my previous post. Unless very lucky with the room or the room is heavily treated, including low bass traps, FQ response and decay (to name just two - most important IMO) will not be that great.

So if you don't like the overall performance of the most directional setup, next step is to keep adding support from other speakers and subs until you get to the point where it is balanced. As @JRowland noted, stretching L and R low support to the max (but having in mind the SPL and distortion as well) would be beneficial to retain as much spacial clues as possible.

 

[JRowland]

stretching L and R low support to the max (but having in mind the SPL and distortion as well) would be beneficial to retain as much spacial clues as possible.

I believe, as @jhaider pointed to, compression at high SPL is probably more of a concern than the distortion.

 

[Oddball]

I believe, as @jhaider pointed to, compression at high SPL is probably more of a concern than the distortion.

Agreed - I wish we had more speaker reviews with compression tests. Solid subs reviews provide that.

I am still worried about distortion at high SPL though, even in the low end. What we have been told is that around/below 20hz distortion does not really matter. Assuming that is right, it still remains a question how much THD above that is audible. I started with 2 subs in my room and they were struggling. SPL was probably almost there, but it was not clean or controlled. 3rd sub would probably do the job, but then decided to go with 4 and do a partial DBA to clean up some decay as well (all before ART). 4 of them are really doing a great job and headroom is evident as they are set between 50-70% output, depending on distance.

Some screenshots from review of SVS PB 4000 to illustrate above. I have 2 SVS PC 4000 which are supposed to be the same in a different form factor. Other two subs are Arendals 1723 2V which are, generally, similar to these.

EDIT: Link to full review of SVS PB 4000

SVS PB-4000 Ported Subwoofer Review

The SVS PB-4000 is the latest evolution of a powerful subwoofer design that has stood the test of time. Read our in-depth review with measurements to see how SVS improved on their classic design.

www.audioholics.com

 

[JRowland]

Agreed - I wish we had more speaker reviews with compression tests. Solid subs reviews provide that.

I am still worried about distortion at high SPL though, even in the low end. What we have been told is that around/below 20hz distortion does not really matter. Assuming that is right, it still remains a question how much THD above that is audible. I started with 2 subs in my room and they were struggling. SPL was probably almost there, but it was not clean or controlled. 3rd sub would probably do the job, but then decided to go with 4 and do a partial DBA to clean up some decay as well (all before ART). 4 of them are really doing a great job and headroom is evident as they are set between 50-70% output, depending on distance.

Some screenshots from review of SVS PB 4000 to illustrate above. I have 2 SVS PC 4000 which are supposed to be the same in a different form factor. Other two subs are Arendals 1723 2V which are, generally, similar to these.

View attachment 521865View attachment 521866View attachment 521867

EDIT: Link to full review of SVS PB 4000

SVS PB-4000 Ported Subwoofer Review

The SVS PB-4000 is the latest evolution of a powerful subwoofer design that has stood the test of time. Read our in-depth review with measurements to see how SVS improved on their classic design.

www.audioholics.com

If I understand things right distortion removes energy but also adds energy in harmonics that can/will screw up the ART algorithm. Also my understanding (I could be way wrong and I hope somebody corrects me if i am) is that compression removes energy (signal ART is expecting) and that occurs before that extra distortion energy would be added. That would also whack out the ART algorithm and generally occurs first, again from my limited understanding and non scientific experimentation.

I know what I hear when I start driving my speakers too far (and also when I do drive them too far - audible distortion). When I start to overdrive them what I notice is I add volume to the knob but don't get back the output that I normally would or what I expect. When I then back off there comes a point where the sound opens back up and everything sounds "right" again. I'm just a hobbyist and mainly a music listener, the whys and hows of some of the science I enjoy learning from this site. It really gives me a headache at times though and isn't enjoyable but I feel it is important enough for me to grasp at least the basics so I can shoot for the best mediocrity I can get if that makes sense. Hopefully I am grasping somewhat blindly in the general vicinity of the straw.

 

[90sNintendoKid]

That is what Dirac recommends even for a single position and is consistent with experience people had for other room EQ systems. You spread the measurements tight around your head and probably at least +/- 20 cm up/down and L/R. After all you don't want to be missing on anything if you just happen to move your head.

Than there is this moving microphone method that many rave about...But it reminds me too much of a shaman doing their ritual so have never tried it, apparently at my own peril.

I’ve found the Magic Beans True Target Dirac ART 2 pass method which uses the moving mic method for nearfield and MLP measurements with that Dirac measurement pattern to be awesome and better than standard Dirac ART.

I will be doing a new Dirac ART calibration soon, I can post the post EQ measurements here.

 

[kifeep]

Let's say you have 4096 taps at 96kHz. The bin size is Fs/n = 96000/4096 = 23.4Hz. In other words, you would be correcting in 23.4Hz chunks - clearly not enough resolution for bass correction.

Now suppose we divide the incoming signal into two. One for <200Hz, and another for >200Hz. We assign half the taps to each (2048). And while we are at it, let's drop the sample rate for the <200Hz part to 1kHz (still well above the Nyquist freq). Now the bin size is 1024/2048 = 0.5Hz.

Disclaimer: I have the paper for multirate filters, and I have tried to read it, but the maths went a little bit over my head. That's about what I understood from it. Maybe someone with more DSP expertise can come along and correct me if i'm wrong.

That's a neat trick. TBH, it makes me a bit more willing to buy into the Dirac ecosystem, since similar resolution seems to only be possible on other systems with very high tap counts.

 

[levimax]

I am still worried about distortion at high SPL though, even in the low end.

The LF distortion thing fascinates me. Many of the same people that chase around SINAD of > 100 for electronics are OK with SINAD of < 10 for their subwoofers. In a way harmonic distortion at LF is more audible than it is at higher frequencies because of the Fletcher-Munson curve. The second harmonic of a 20 Hz tone is 40 Hz which we are 20 dB more sensitive to. The distortion levels from many consumer grade subs is so high that when playing 20 Hz the 40 Hz distortion is perceived louder than the fundamental. I have read that many people actual "prefer" this because it makes the bass sound louder and or that is what we are used to hearing. It appears that it all comes down to Hoffman's Iron law and the overwhelming preference for small enclosures which supersedes everything else. It is trivially easy to get LF with high SPL and low distortion with a large enclosure and large driver. With small enclosures it takes heroic efforts and rapidly becomes futile as the enclosure and driver get smaller.

I built some giant subs that can play loud and clean and low and they sound different than the SVS SB 3000 subs they replaced. Whether or not this difference is "worth it" is debatable but after getting used to clean LF I find it distracting to go back to high distortion bass. For most recordings without a lot of LF content it really doesn't make much difference but for recordings with a lot of LF content the difference is quite noticeable.

To me it seems like the "solution" is IB (Infinite Baffle) subwoofers. Fantastic performance without taking up any space and not really expensive. Only issue is not possible in every situation but for many HT applications it probably is. IB subs will probably be my next experimental project.

 

[Oddball]

The LF distortion thing fascinates me. Many of the same people that chase around SINAD of > 100 for electronics are OK with SINAD of < 10 for their subwoofers. In a way harmonic distortion at LF is more audible than it is at higher frequencies because of the Fletcher-Munson curve. The second harmonic of a 20 Hz tone is 40 Hz which we are 20 dB more sensitive to. The distortion levels from many consumer grade subs is so high that when playing 20 Hz the 40 Hz distortion is perceived louder than the fundamental. I have read that many people actual "prefer" this because it makes the bass sound louder and or that is what we are used to hearing. It appears that it all comes down to Hoffman's Iron law and the overwhelming preference for small enclosures which supersedes everything else. It is trivially easy to get LF with high SPL and low distortion with a large enclosure and large driver. With small enclosures it takes heroic efforts and rapidly becomes futile as the enclosure and driver get smaller.

I built some giant subs that can play loud and clean and low and they sound different that the SVS SB 3000 subs they replaced. Whether or not this difference is "worth it" is debatable but after getting used to clean LF I find it distracting to go back to high distortion bass. For most recordings without a lot of LF content it really doesn't make much difference but for recordings with a lot of LF content the difference is quite noticeable.

To me it seems like the "solution" is IB (Infinite Baffle) subwoofers. Fantastic performance without taking up any space and not really expensive. Only issue is not possible in every situation but for many HT applications it probably is. IB subs will probably be my next experimental project.

20hz is a difficult frequency, and for flawless reproduction in that range that one would need to get probably 21" subs in big enclosure. I am really chasing 25hz and above due to constraints of my room. 6 13.5/13.8 drivers and 5kW of power seem to do a great job reducing the load, providing the headroom and from what I hear, reducing the distortion to levels that can not be audibly detected.

Obviously, the bigger the subs, the lower the natural distortion will be. But than there is also approach to build the system based on 4 subs (D&M limit) that will get you to where you aim to be. For smaller rooms it could be even two SVS PB 1000s that will get your there. For larger spaces, especially irregular, one should not count with room gain, but quite the opposite.

 

[levimax]

20hz is a difficult frequency, and for flawless reproduction in that range that one would need to get probably 21" subs in big enclosure. I am really chasing 25hz and above due to constraints of my room. 6 13.5/13.8 drivers and 5kW of power seem to do a great job reducing the load, providing the headroom and from what I hear, reducing the distortion to levels that can not be audibly detected.

Obviously, the bigger the subs, the lower the natural distortion will be. But than there is also approach to build the system based on 4 subs (D&M limit) that will get you to where you aim to be. For smaller rooms it could be even two SVS PB 1000s that will get your there. For larger spaces, especially irregular, one should not count with room gain, but quite the opposite.

Any chance to try IB subs? Probably not, as I think the pictures of your place show it to be a high rise, but attics can make a great large enclosure.

 

[Oddball]

If I understand things right distortion removes energy but also adds energy in harmonics that can/will screw up the ART algorithm. Also my understanding (I could be way wrong and I hope somebody corrects me if i am) is that compression removes energy (signal ART is expecting) and that occurs before that extra distortion energy would be added. That would also whack out the ART algorithm and generally occurs first, again from my limited understanding and non scientific experimentation.

I know what I hear when I start driving my speakers too far (and also when I do drive them too far - audible distortion). When I start to overdrive them what I notice is I add volume to the knob but don't get back the output that I normally would or what I expect. When I then back off there comes a point where the sound opens back up and everything sounds "right" again. I'm just a hobbyist and mainly a music listener, the whys and hows of some of the science I enjoy learning from this site. It really gives me a headache at times though and isn't enjoyable but I feel it is important enough for me to grasp at least the basics so I can shoot for the best mediocrity I can get if that makes sense. Hopefully I am grasping somewhat blindly in the general vicinity of the straw.

Well compression is just inability of the speaker to produce more output/energy. ART is generally not counting on these circumstances as it will adjust its filters by the sweep that is not at high SPL. Same with distortion - it will not measure distortion, just the FQ response capabilities. So both of these have to be extrapolated into building filters and determining support low levels if the desired SPL is in excess of the sweeps.

I think you nailed it as to the point where you start driving speakers too hard. It is exactly as you note - at least in my experience.

 

[Oddball]

Any chance to try IB subs? Probably not, as I think the pictures of your place show it to be a high rise, but attics can make a great large enclosure.

Lol, perhaps in the next house. As you said, what I have in the high-rise is already bordering excessive. We are looking to relocate to a house, but my wife is so picky that it makes it a very difficult project. With the house, I would have the opportunity to build adjacent building for HT, which would be my audio dream.

 

[No_hair_left]

Im completely lost with the grouping, Im assuming I leave the group 6 subs alone and uncheck everything?

In my front l/r (group 1) I have checked the Group 3 box (side surrounds) and the group 6 box(subs) but seeing as the surround are much further back am I supposed to do this?

Or is it really a case of the separate groups support nothing but the subs?

and the atmos just support each other?

I am lost

Also lots of talk about dirac making bass better but in my case with the gravity test the heartbeat in the beginning seems incredibly muted, definitely have more to learn it seems, I have probably watched about 4 hours of videos and still dont understand lol

 

[Flak]

ART will disregard directional bass setting on D&M bass management, as well as any other settings like crossovers. So that's not a way to go directional with ART.

The most directional 2.2 setup, as you say, would be to create profile/calibration with 4 groups. L, R, L sub and R sub (subs being right by L/R speakers). Then support L with L sub and R with right sub. This is pretty much guaranteed to provide you with maximum "spaciousness". However, as @thcdru2k noted, this is a trade off with the overall performance of traditional cross-support ART system - which I also noted in my previous post. Unless very lucky with the room or the room is heavily treated, including low bass traps, FQ response and decay (to name just two - most important IMO) will not be that great.

So if you don't like the overall performance of the most directional setup, next step is to keep adding support from other speakers and subs until you get to the point where it is balanced. As @JRowland noted, stretching L and R low support to the max (but having in mind the SPL and distortion as well) would be beneficial to retain as much spacial clues as possible.

Directional Bass is also commented on here at 37:20

 

[smygolf]

Im completely lost with the grouping, Im assuming I leave the group 6 subs alone and uncheck everything?

In my front l/r (group 1) I have checked the Group 3 box (side surrounds) and the group 6 box(subs) but seeing as the surround are much further back am I supposed to do this?

Or is it really a case of the separate groups support nothing but the subs?

and the atmos just support each other?

I am lost

Also lots of talk about dirac making bass better but in my case with the gravity test the heartbeat in the beginning seems incredibly muted, definitely have more to learn it seems, I have probably watched about 4 hours of videos and still dont understand lol

I would say let LCR and subs act a support on all groups. (with a smaller C do not use it as support)
Do not use atmos as support, not even support within the atmos group.
And i do not let surround support each other but they give support @ 100-150hz

Since the decay is much lower a tad higher lvl in the bass can be needed.

 

[No_hair_left]

I would say let LCR and subs act a support on all groups. (with a smaller C do not use it as support)
Do not use atmos as support, not even support within the atmos group.
And i do not let surround support each other but they give support @ 100-150hz

Since the decay is much lower a tad higher lvl in the base can be needed.

My lcr are arendal 1961 monitors so they are all smaller really.

So It would look something like this then?
Increase the sub support a little
Leave the 2 atmos groups all unchecked at their 120hz crossover
Leave the surround channels unchecked at their 80hz crossover
Have l/r at their 80hz crossover support all channels, including atmos? center is a possibility.

The group 6 box for me is the subs I'm assuming I uncheck that completely as I don't want speakers trying to support my subs.