Dirac Research Questionnaire

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

cjf said:

I'm curious what your definition of "Top End" is? Where would you say that starts on the scale numerically?

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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.

cjf said:

I'm also curious what amplifiers you might be referring to that have DSP builtin? Do you mean an Integrated Amp/AV Receiver?

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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.

cjf said:

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?

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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!

cjf said:

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.

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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.

DonH50 said:

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.

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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

cjf said:

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.

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Possible with passive crossover before RC DSP and separate bass and non-bass amps.

cjf said:

I can tell you with 100% confidence that my rig sounds significantly better everywhere in the Freq scale with DSP/Room correction enabled.

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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.