Dirac Research Questionnaire

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Feb 14, 2020
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I received by email today a questionnaire from Dirac Research - I expect many here have also received this. It has given me an opportunity to explain exactly why I believe (and confirmed by simply listening carefully) that Dirac and its competitors, when built into full-range amps, are bad for ultimate sound quality.

I've expressed my views here on this and other forums and explained why this spoiling of ultimate sound quality may be. No one has challenged my theory, but many have said that their own systems have benefited from Room Correction DSP.

I beg anyone who is using Dirac user (or RoomPerfect or MARS or any other RC DSP built into full-range amps and who has first class speakers) to do this simple test. Listen to exciting music with not much bass (whatever should be giving you goose-bumps) with the filter engaged and then with the filter not engaged and back again. Try to ignore the bass (the area where RC adjusts for poor room acoustics) and concentrate solely on the top end - where the goose-bump factor is generated - and see what you think.

I've tried Room Perfect, Dirac and MARS and all have damaged the important top end of the frequency range just enough to reduce or to lose this goose-bump factor, even though the processor doesn't ADJUST the signal above the bass frequencies - 500 Hz in my version of Dirac Live.

I don't disagree that the job of adjusting for poor room acoustics can be simplified by RC DSP and that those with multi-speaker systems (2 channel plus subs, or AV systems) may find conventional tuning very difficult and RC DSP makes the job simple with an apparent immediate "improvement" in sound, but critical listening will (in my experience as well as others) reveal that the top end is damaged by this extra (and totally unnecessary for high frequencies) stage of signal processing, in a similar way that tone controls and graphic equalisers of the past used to. Any extra signal processing is fundamentally a bad thing!

If (and only if) the frequency range is spilt (by active crossover) first and the bass only is sent to the RC DSP and then onto the bass amp and driver, while the higher frequencies continue unmolested by DSP to their own amp and drivers can this problem be avoided. This is probably why those few speakers on the market that have amps and DSP inside their cabinets sound so good. They perform room correction the “proper” way by processing only the bass. Speakers that do this include Dutch & Dutch, Kii and Avantgarde XD range. More will follow. Perhaps the KEF LS60 (the subject of another current thread) also does – I’ve not investigated.

I’d invite anyone with first-class speakers capably of generating goose-bumps for itheir listener to do the test I’ve described and respond with your unbiased and subjective findings. You may well think on balance that RC DSP improves the overall sound, but does it spoil the top end in the process? Thanks. Peter
 
Dirac Live uses "curtains" so you can limit the correction to just the bass region. Seems like that would solve your problem? That is many folk who use Dirac Live advocate for, correcting just the bass, and leaving the normal listening range untouched.
 
I'm curious what your definition of "Top End" is? Where would you say that starts on the scale numerically?
I'm also curious what amplifiers you might be referring to that have DSP builtin? Do you mean an Integrated Amp/AV Receiver?

I imagine many people here fall into an age bracket where most sounds above 12-15khz are all but a distant memory from days gone by. Not sure anyone who fits this description can really make a concrete decision on what they think they might be hearing in that Freq range whether using DSP or not.

Have you taken any room measurements before and after the filters were enabled and noticed a difference between the two modes in the upper freq range?

I think all of those Active Monitors you listed have the same general flaw. That being, they have freq limited AD/DA converters built into them. In the case of Dutch and Dutch, they are/were limited to 24/48 according to the last Stereophile review. Some others are generous enough to at least give you 24/192 (Genelec being one).

The funny thing is, I dont have anything against any of the lower Freq limitations listed. My issue is that I dont want my speakers making that decision for me.
 
I'm curious what your definition of "Top End" is? Where would you say that starts on the scale numerically?
Probably a poor choice of words., I should have said "non-bass", meaning all frequenciees above the bass range where DSP may be helpful. This could be influenced by the DSP software (eg 500 Hz with my version of Dirac) or the crossover frequency chosen for the bass driver.

I'm also curious what amplifiers you might be referring to that have DSP builtin? Do you mean an Integrated Amp/AV Receiver?
I'm mu own case, I have used integrated amps with DSP and DAC built in (I listed the models in the first post), but the same applies if the box containing the RC DSP is anwhere between the source signal and a single full-range amp. It's when the full-range signal is sent through the DSP that I believe adversely affects the upper frequencies that deliver the goosebump factor.
Have you taken any room measurements before and after the filters were enabled and noticed a difference between the two modes in the upper freq range?
No, because I can't do that with the mic and software provided with my NAD M33. I would need a calibrated mic and independent software such as REW. However, I don't think measurement would identify what I'm driving at. It's the characteristic of the music after DSP that concerns me. The reduction in speakle, goosebump factor (call it what you like) is unlikely to be seen on a computer screen!
I think all of those Active Monitors you listed have the same general flaw. That being, they have freq limited AD/DA converters built into them.
I have not personally spent much time with these speakers, but have just read reviews. If they use a poor DAC, I'd be surprised - and disappointed if I was a potential buyer! I wouldn't need an ADC as I don't use analogue, but presumably if the one on the D&D was poor, any analogue signal could be digitised before reaching the speakers.
Dirac Live uses "curtains" so you can limit the correction to just the bass region. Seems like that would solve your problem? That is many folk who use Dirac Live advocate for, correcting just the bass, and leaving the normal listening range untouched.

You've missed the point! My own version of Dirac adusts only sub 500 Hz, but the entire full-range signal has to pass through the DSP. It's that that I believe is the cause of reduction in ultimate sound quality. Above 500 Hz (or wherever you choose to allow Dirac to stop making adjustments) should be allowed to bypass the processor altogether and reach its own amp unmolested by DSP, while the bass only gets DSP'd and proceeds to its own amp.

I hope someone will sometime do the simple test I suggested in my opening post, rather than bring red herrings into the discussion! The points raised so far, with rspect, are covered in my top post and the object was to invite members to critically listen to exctitin, low bass music through their own high quality speakers with and without their DSP filter. In my own case, there's a Setting in the app that requires a single click to move from Dirac Filter to No Filter. Thanks. Peter
 
You've missed the point! My own version of Dirac adusts only sub 500 Hz, but the entire full-range signal has to pass through the DSP. It's that that I believe is the cause of reduction in ultimate sound quality. Above 500 Hz (or wherever you choose to allow Dirac to stop making adjustments) should be allowed to bypass the processor altogether and reach its own amp unmolested by DSP, while the bass only gets DSP'd and proceeds to its own amp.

I hope someone will sometime do the simple test I suggested in my opening post, rather than bring red herrings into the discussion! The points raised so far, with rspect, are covered in my top post and the object was to invite members to critically listen to exctitin, low bass music through their own high quality speakers with and without their DSP filter. In my own case, there's a Setting in the app that requires a single click to move from Dirac Filter to No Filter. Thanks. Peter
I have done that test, Dirac Live on/off with correction limited to ~200 Hz, and in my system and room to my ears it works better with Dirac Live on. Subs and mains are better integrated and I did not detect any loss of performance above the correction set point. I figured that would be implied but obviously not, sorry for the "red herring". Without Dirac Live I was able to integrate the subs using their own phase adjustments but it was much more work and, to avoid any DSP at all, I had to use an external analog crossover to the mains.

If you use any room correction system the signal passes through the DSP but all that is done is to align the delays of the various speakers. If you have a fully-analog system and feel any conversion to digital is detrimental than you should not be using room correction programs (processing).

Sorry, out - Don
 
You've missed the point! My own version of Dirac adusts only sub 500 Hz, but the entire full-range signal has to pass through the DSP. It's that that I believe is the cause of reduction in ultimate sound quality. Above 500 Hz (or wherever you choose to allow Dirac to stop making adjustments) should be allowed to bypass the processor altogether and reach its own amp unmolested by DSP, while the bass only gets DSP'd and proceeds to its own amp.
Unfortunately I dont think what you describe is possible with two channel source material. Since the full Freq range is present in both channels its going to need to pass thru some form of DSP if you intend to try and send 500hz and below to the Sub/Subs only.

To do what you describe I believe you need to, at minimum, start with multi-channel source material. Then you need a multi channel DAC to be able to send each channel out to dedicated amp/amps.

I have multiple channels in my rig but I'm not a multichannel source material owner. I couldnt comment on whether or not each channel of a multi channel disk only contains a certain band of the Freq scale. I believe this would be a requirement though in order to not have to send certain Freq ranges thru DSP somewhere in the chain.

I'm already well aware of how my rig sounds with and without DSP engaged. I can enable and disable it with the flick of a switch on my phone while sitting in the main listening chair with almost no delay. I can tell you with 100% confidence that my rig sounds significantly better everywhere in the Freq scale with DSP/Room correction enabled.
 
Unfortunately I dont think what you describe is possible with two channel source material. Since the full Freq range is present in both channels its going to need to pass thru some form of DSP if you intend to try and send 500hz and below to the Sub/Subs only.
Possible with passive crossover before RC DSP and separate bass and non-bass amps.
I can tell you with 100% confidence that my rig sounds significantly better everywhere in the Freq scale with DSP/Room correction enabled.
I'm sure that RC DSP pays dividends with multi channel material, but my 2 channel system clearly loses a little of its top-end sparkle (what I described earlier as goosebump factor) when I engage the filter, despite the DSP only adjusting below 500 Hz. It's that top end sparkle I want to retain, so I keep DSP off and accept that the lower frequency range may not be dead flat. But of course tuning of my 2 speaker system is very much simpler that a system with multiple speakers. I have worked hard to get speakers best placed and oriented, plus room furnishings appropriate for good sound - without resorting to artificial room treatment. But thanks for your findings.
 
Possible with passive crossover before RC DSP and separate bass and non-bass amps.

I'm sure that RC DSP pays dividends with multi channel material, but my 2 channel system clearly loses a little of its top-end sparkle (what I described earlier as goosebump factor) when I engage the filter, despite the DSP only adjusting below 500 Hz. It's that top end sparkle I want to retain, so I keep DSP off and accept that the lower frequency range may not be dead flat. But of course tuning of my 2 speaker system is very much simpler that a system with multiple speakers. I have worked hard to get speakers best placed and oriented, plus room furnishings appropriate for good sound - without resorting to artificial room treatment. But thanks for your findings.
I know this is an old discussion but I wanted to know if you found a solution to this issue?

I too have come across what you have experienced and it is night and day. I will describe how I came across this which led me to seeing if there was anyone else experiencing this and well here I am.

Okay so here's the gear:
Marantz Cinema 50
VTV 2 Channel amp
Klipsch RP8000f with a home brew custom crossover I design with air coil inductors all high quality components.
Dirac Live! Full bandwidth and Bass control

Now like everyone else Dirac live! made everything clear, nice center image, tight bass etc. I didn't know better nothing to compare besides my old Klipsch factory cross over and old Yamaha rxv6a. It seemed like an obvious difference in sound I couldn't deny especially now that I unlocked more performance with my crossover.

However I came across a buried YouTube video of a man named Bob from myspeakersetup.com that had a seminar on speaker placement in a room that's not treated not symmetrical etc. He explained how you get her an almost holographic sound stage and pinpoint center imaging with a rich delivery following his technique. So I thought hell why not try it. So I turned my dirac filter to off and made sure my full range was set to on in my towers and put the AVR to pure direct. Now with both speakers in that perfect triangle and slightly towing in to the listening as almost all of use do to get it how we want made the center image sound like it was just coming from both speakers. Of course timing seemed odd no matter how perfect you place the speakers measuring it perfectly in distance from each other to listener to angle. Now I tried Bobs speaker placement technique that accounts for the room shape, size and reflections. I ended up with my left speaker pointing directly at my left ear and my right speaker away from my right ear and about 3 inches closer to the listening position. It looks weird let me tell you. However now playing songs OMG. The center is so smooth and rich coming from a horn! The sound stage open and so dynamic you hear all the effects literally all around you even behind your head. It was truly transformative like going from no bass control to bass control for your subs. Now when I flip to Dirac with filter on it lost all the richness it sounded thin in vocals and the effects are there but again thin. I believe Dirac tries to compensate for the room but in doing so it has to cut off certain frequencies when your speakers are set perfect in a non perfect room! Most of us don't have perfect rooms even if you can treat some areas. I would never thought I missed anything if I had tried this. I encourage you to try it yourself. So of course I thought okay what if I keep my new speaker layout that account for the rooms psychoacoustics with Dirac? Well 2 things happen. 1 Dirac tries to correct the timing and imaging of something I technically manually perfected for the room characteristics and sounds again like thin like it just cleans up all the fun and liveliness in the vocals and sound effects. I tried only using bass control from 20-300hz and that doesn't matter. Duract still automatically put the speaker in "small range" no matter what. So full range is not just about the speakers ability to play low but as this thread indicated it's also creating a richness around ALL spectrums of each frequency with it is what I have realized. This I think becomes more evident in my case with the high quality crossover I built that unlocked more from this speaker. So ideally Dirac would be great if I can give the option to go full range rather than lock you in automatically in small range. This would be amazing especially in movies I bet. It literally lifts the hairs up. I wish Dirac would realize this important element and look into it. The new Dirac ART helps with bass which I look forward to but again the upper frequencies are lacking big time and unless you have a good pair of speakers I don't think you will hear a difference.
 
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Interesting observations and your experience reflects my own. All "room correction DSPs" that require the entire full-range signal to pass through the signal processer, even though you may choose to allow adjustments below 200 or 500 Hz, cause damage to the top end. It's the top end of the range that in my experience suffers from having to endure this unnecessary extra processing and the loss in top end detail results in a reduction in the goosebump effect that we strive for. I've used Dirac Live, Anthem, RoomPerfect and MARS and all "accidentally" spoil the top end to a small extent. I prefer not to engage any processsor that requires the entire frequency range to pass it. The only way to avoid this is to cross over at a very early stage actively, and send only the bass to a DSP and then to its bespoke amp, while the upper range does directly (without DSP) to its own amp.
 
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Interesting observations and your experience reflects my own. All "room correction DSPs" that require the entire full-range signal to pass through the signal processer, even though you may choose to allow adjustments below 200 or 500 Hz, cause damage to the top end. It's the top end of the range that in my experience suffers from having to endure this unnecessary extra processing and the loss in top end detail results in a reduction in the goosebump effect that we strive for. I've used Dirac Live, Anthem, RoomPerfect and MARS and all "accidentally" spoil the top end to a small extent. I prefer not to engage any processsor that requires the entire frequency range to pass it. The only way to avoid this is to cross over at a very early stage actively, and send only the bass to a DSP and then to its bespoke amp, while the upper range does directly (without DSP) to its own amp.
What did you do to bypass early? I'm not familiar with this process if you don't mind telling me what to do?
 
What did you do to bypass early? I'm not familiar with this process if you don't mind telling me what to do?
I can't achieve that as long as I use my DSP-enabled amplifier to deliver the full frequency range. However I do have another option, thanks to my loudspeaker design.

My speakers are of a hybrid design that separates the incoming signal into bass (sub 170 Hz) and the rest. The rest can go straight to the horn section while the bass goes to a dedicated amplifier that includes Avantgarde's own DSP, identified by the XD tag.

Unfortunately XD is rather complex and relies on REW measurements to identify where adjustments are required. These adjustments have to be made by taking the flat response line found in the XD software and moving sections of the line up or down to compensate for dips and troughs in measured response. All a bit of a faff unless you enjoy this constant measurement regime! Personally I prefer to set speakers up as best I can and just listen to the music, even if there are a few imperfections.

The latest AG G3 Series speakers that are now optionally fully active using their iTron amplification, also feature DSP for the bass section, but my reading of the User Manual suggests that it is much simpler than the XD software for my speakers.

Meanwhile, I am leaving XD flat and experimenting with the various options for wiring up my system and perhaps looking at DL if I think I'm failing in getting my speakers to perform as well as they are capable of. I've just added my REL subs using their own built-in XO to reduce the incoming range from 170 Hz to about 60 Hz (though REL's controls have no indicative markers) and I'm pleased with the sound though doubtless still room for improvement. I'll run REW and / or DL measurements to see what's actually going on, though I'll try to make further adjustements without resorting to DL
 
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I can't achieve that as long as I use my DSP-enabled amplifier to deliver the full frequency range. However I do have another option, thanks to my loudspeaker design.

My speakers are of a hybrid design that separates the incoming signal into bass (sub 170 Hz) and the rest. The rest can go straight to the horn section while the bass goes to a dedicated amplifier that includes Avantgarde's own DSP, identified by the XD tag.

Unfortunately XD is rather complex and relies on REW measurements to identify where adjustments are required. These adjustments have to be made by taking the flat response line found in the XD software and moving sections of the line up or down to compensate for dips and troughs in measured response. All a bit of a faff unless you enjoy this constant measurement regime! Personally I prefer to set speakers up as best I can and just listen to the music, even if there are a few imperfections.

The latest AG G3 Series speakers that are now optionally fully active using their iTron amplification, also feature DSP for the bass section, but my reading of the User Manual suggests that it is much simpler than the XD software for my speakers.

Meanwhile, I am leaving XD flat and experimenting with the various options for wiring up my system and perhaps looking at DL if I think I'm failing in getting my speakers to perform as well as they are capable of. I've just added my REL subs using their own built-in XO to reduce the incoming range from 170 Hz to about 60 Hz (though REL's controls have no indicative markers) and I'm pleased with the sound though doubtless still room for improvement. I'll run REW and / or DL measurements to see what's actually going on, though I'll try to make further adjustements without resorting to DL
Very interesting how you're going about to tackle the issue. Yes I find even when you get close there's always something you know can be better because you heard it better before and not just a hunch. It's just getting it all there is the challenging part. Well I wish you the best in your trial and error. If you figure it out please share I'm sure someone will benefit from it if not simply bring awareness to this dilemma!

Cheers!
 

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