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    Dirac Live 2 Digital Room Correction Software Walkthrough

    Dirac 2 is the latest version of Dirac’s Digital Room Correction (DRC) technology. In this article, I walk through the steps of using Dirac to optimize the response of the Purifi SPK4 demo kit that I recently reviewed here on Audiophile Style.


    Can we make an already great sounding speaker sound better in my room? And by better I mean smoothing out the low frequency response below the room’s transition (Schroeder) frequency, making small, broad band tonal adjustments in the midrange and top end to be a bit smoother and finally a timing correction of the impulse response.


    The short answer is yes we can. We can see the improvement in the measured frequency and timing response. I can also hear an audible difference with a tighter, more clear sounding bass, smoother overall frequency response and a more coherent timing response (i.e. stereo imaging and depth of field) across a larger sweet spot.  


    With Dirac 2, designing and generating a partial correction from about 600 Hz on down below the room’s transition frequency is as simple as it gets. The sonic benefits are instant, much smoother bass response with no huge peaks and dips that plague virtually every room below Schroeder frequency. Full range correction comes with improved phase response (i.e. imaging and depth of field) covering a wider sweet spot, more on that in the subjective listening section.


    Before the walkthrough, let’s talk a bit about Dirac’s room correction technology.



    Technology Discussion


    First, what audio problem is room correction technology designed to solve? The unfortunate reality is that below a room’s transition (a.k.a. Schroder) frequency, the room controls the bass response arriving at your ears, not the loudspeakers. Due to modal resonances we get wildly different bass responses depending on where we place speakers in rooms relative to the listening position:






    The above chart is from Floyd Toole’s Audio Science Article.  As Floyd says, “In the investigation of many rooms over the years, I would estimate that something like 80% have serious bass coloration.” For those of us that take acoustical measurements of audio systems, this comes as no surprise. The peaks and dips in the low frequency response is typical and exists in virtually every room that was not specifically designed using proper room ratios, aside from construction and acoustic treatments.


    Room modes are calculated based on one’s room dimensions where room resonances take control of the low frequency response regardless of the speakers being used. I like this Room Mode calculator as you can move the cursor along the frequency scale and it will output a tone at that frequency. If your computer is hooked up to your speakers (careful with the volume!), you can hear the resonances in your room by hovering the cursor over the modes in the graph. It is an ear opening experience and great for training ones ears to know what to listen for.


    Room modes can sound like “one note bass” where the room mode is so bad, all you hear is the single droning bass note that drowns everything else out. Or the “where did the bass go?” when certain bass notes are played. Or simply just uneven bass, some notes are there, some are gone, and some are too loud.


    Dirac 2 is designed to smooth out the peaks of the low frequency room response and fill in some of the dips across the listening area. Our ears are more sensitive to peaks than dips. A good primer on why we hear what we hear in small room acoustics as it relates to room correction is James (JJ) Johnston’s, “Acoustic and Psychoacoustic Issues in Room Correction.” Download the PowerPoint if you can. The first 31 slides are worth the read.


    Dirac uses a “mixed phase” filter approach which is a combination of IIR filters and FIR filters for efficiency. The white paper linked goes into detail behind the design, and can be summarized as:


    A first main aim is to control not only the frequency domain properties of the system but also the time domain properties: The impulse responses as measured at different listening positions. In particular, we strive to reduce the “pre-ringings” (pre-echoes) that would otherwise result in an un-natural sound experience. 


    Secondly, we use dynamic models of the sound system that are based on measurements at multiple listening positions. This is important for obtaining a robust design that works over an extended region to provide a large spatial area with good sound quality. 


    Third, we may jointly optimize multiple loudspeakers to better control the sound pressures at different listening positions. This is done by precise phase control of the individual loudspeaker transfer functions at low frequencies. Joint optimization of a set of loudspeakers results in more distinct bass performance, better robustness of the compensation and better control of the impulse responses at different listening positions.


    Room correction is a complicated (and mostly misunderstood) subject area. If there is interest, I might write another article to discuss this in more detail as it is not just “eq” that is being applied here (i.e. the time domain properties are equally important).

    Dirac 2 consists of two pieces of software that work together. The Dirac Live Processer (DLP) is a VST plugin that “hosts” the correction filters in a convolution engine. The Dirac Live application is used to measure your loudspeakers in your room, design the filters, and upload the correction filters to the DLP.


    One interesting difference to other convolution engines is that the DLP accounts for any latency issues, so when switching the DLP on or off, the audio change is instant as opposed to a ¾ second silence gap with a 65K tap FIR filter. There is also no latency when switching between filters, which makes A/B comparisons easy so you can “bracket” in on your preferred frequency response in a shorter period of time.


    Since the Dirac Live Processor is a VST plugin, any software music player or Digital Audio Workstation (DAW) that supports the VST plugin architecture can simply load the DLP. In this article, I am using JRiver Media Center 64 Bit DSP audio architecture to host the DLP:







    I clicked on Manage Plug-ins in JRiver and navigated to where the DLP VST was installed and loaded it. Here we are seeing the DLP loaded into JRiver and active with a correction uploaded into the first of eight slots available.


    The 2nd piece of Dirac Live is an application that you run on your computer that is mostly “wizard” driven, and steps you through the process of:

    1. Connecting and configuring audio I/O 
    2. Adjusting playback and record levels 
    3. Select the type of measurements you want to take (i.e. chair, couch area, etc.) 
    4. Taking the measurements 
    5. Designing a correction filter whether partial or full range using a target of your preference  
    6. Examining the results of the correction in a simulation
    7. Uploading the correction filter to Dirac Processor
    8. Managing measurements, targets, corrections, etc.


    So let’s perform step 1 of the Dirac Live application wizard in the objective measurements section



    Objective Measurements





    For the measurements, I moved the couch and coffee table out of the way and the sub woofers are not active.


    This is the main screen you see once you have downloaded Dirac Live, installed it and connected to the DLP. Note that you are required to login to your Dirac Live account in order to connect to the DLP. Also, in order for the Dirac Live application to communicate with the DLP, the latter needs to be enabled and actively receiving an audio signal. Meaning that the DLP is enabled in JRiver and music is playing through Dirac Live Processor so it is “active.” Without the DLP being active, the Dirac Live application cannot connect to the DLP.








    Each step of the wizard comes with a help screen of what to do. It is concise and well written so you can quickly get the hang of what to do. Here we are selecting which recording device to use once we clear the instructions:







    Here I am using my Lynx Hilo ADC with a microphone preamp and calibrated measurement microphone. I have clicked into the area with the red square and loaded my measurement mics calibration file. In my case, the mic calibration file uses comma separated text whereas Dirac is expecting periods. Easy enough to open in a file editor and replace commas with periods. In most case, like using a UMIK-1 mic, the microphone calibration file will load without any calibration file modifications.


    Next step is to adjust speaker level and microphone gain settings:







    I wholeheartedly agree with “keep the master volume at the lowest setting and gradually increase it.”








    I have pressed play on the left channel and adjusting the levels to be in the “green.” If you have a sound level meter, 75 dB SPL C weighting at the listening position is loud enough and I would not go beyond 85 dB SPL, which to our ears, sounds twice as loud as 75 dB SPL.


    If you don’t have a sound pressure level meter (even a smart phone SPL app will do), then adjust to a comfortable playback volume. If you feel like covering your ears, then it is too loud.


    Clicking on next brings up the type of measurement you would like to take. These involve taking multiple measurements, the number of which depending on what type of listening arrangement is selected. The wider the listening area to cover the more measurements one needs to take. So it could be as few as 5 measurements and as many as 17:








    In this walkthrough, I tried two listening arrangements, a single chair with 5 measurements and the sofa wide imaging with 17 measurements. This is so I could also subjectively compare the two corrections. First lets walkthrough the single chair selection.


    Single Chair







    Click on Proceed to Measure:







    I decided to use the minimum amount of measurements for this setup to test out Dirac’s algorithms. Above, I just completed the 5th measurement. The idea is that you move the microphone relative to the placement as indicated in the diagram. In general, the mic placement is 40 to 60cm apart per placement and you can choose whatever order you want take the measurements by clicking into the location on the diagram. Note that the precise placement of the mic to the location is not crucial.


    As a side note, it is good to temporarily remove any objects between the speakers and the microphone positions, including the chair and or sofa at the listening position. We measure and correct for the loudspeaker and room with an unobstructed path and nothing around the microphone so we are getting a clean as a sound field as possible. We don’t want to correct for any reflections between the speakers and mic due to a coffee table or around the mic itself as that will lead to a colored sound. It is best to measure and correct for the unobstructed sound field first and then return the furniture to its original locations. Finally, I recommend getting a real boom mic stand for taking measurements. You can grab one at your local music store or order online. The little mic stand that comes with the UMIK-1 while cute, is not helpful as you need to place it on something to get ear height, which means reflections (i.e. colorations) are getting into the mic.


    Each time you take a measurement, Dirac will output a sweep signal starting with the left channel, then the right channel, then back to the left channel. So 3 sweeps per location times 5 locations equals 15 sweeps: 








    Here is the screen you see when taking a measurement, with the abort button in case you need to abort the measurement for whatever reason.

    Once you are happy with your measurements, click on proceed to filter design:









    Dirac suggests a target curve based on the measurements you took. Generally speaking, one is looking for a downward tilt of the frequency response at the listening position. This is because most forward firing drivers in loudspeakers start off as omnidirectional at low frequencies and become progressively more directional at higher frequencies. The rising bass energy yields a steady state room curve with a downward tilt. 


    How much tilt? The scientific research that Sean Olive (and earlier Floyd Toole) conducted over years shows that a slope of 20 Hz to around -8 to -10 dB at 20 kHz is what most listeners prefer as neutral sound. A high level overview of that can be found in, The History of the Harman Target. While the overview also discusses headphone target curves, which have the same preferred target (transfer function) as loudspeakers in rooms, it also discusses loudspeaker target preferences. More importantly, there are a listing of AES papers that one can get the details on. One example is the Subjective and Objective Evaluation of Room Correction Products:










    Of course, you are free to implement any target curve you want, but a good starting place is to use Dirac’s suggestion and if it is a bit too bright or dark sounding, one can always adjust the curve. Note that a flat in-room response is not the ideal target response as it will be exceedingly bright sounding. If you read through Sean Olive’s presentation referenced above, and in these slides, it is actually the tilting frequency response that our ears perceive as flat or neutral sounding at the listening position (see slide 25). Well worth the read.


    Looking at the analysis chart below, we are seeing the processed 5 measurements down to left and right, plus the suggested target curve:









    So these wonderful little 15L bookshelf Purifi speakers have a frequency response with the -3dB limits at 25 Hz and 22 kHz. Outstanding for such a small 2 way bookshelf speaker. Ctrl-click both checkboxes, top right to get both curves to display.


    Note the room resonances showing up below 300 Hz in my room and if I were to choose a partial correction frequency, which I have done a bit later, I would choose 600 Hz and below to be corrected as we can see by 600 Hz the “up and down” peaks and dips are no longer an issue. In fact, having been using room correction since 2011, and having seen many other people’s measurements of loudspeakers in rooms, 600 Hz seems to be the most common point where the room starts to have an influence on the frequency response and gradually taking over completely by the time one reaches the rooms transition frequency, which in my room is at 200 Hz. As linked earlier, you can use this room mode calculator to calculate your room’s transition frequency.


    See the bottom right panel where it says on one side measured and corrected on the other side? Dirac has already calculated the correction in the background and by unchecking the measurement and checking on the correction, we get:








    As one can see, a considerably smoother response. So not only smoothing out below 600 Hz, but also bringing down the broadband rise from 2 kHz to 5 kHz when compared to the original measure. Still a little dip left at 100 Hz, but as folks may have read in JJ’s presentation, our ears are not as sensitive to narrow band dips as compared to peaks, so all good. Note the (very) slight channel level difference in the top end frequency response. As @flak has commented here, “Dirac Live 2.x algorithm might even slightly compromise on FR response of one of the speakers in favor of the best possible phase coherence between them that is important for imaging.” We will be exploring that in the subjective listening section.


    Next I clicked on “Proceed to filter export” and here I am exporting the correction filter to DLP. I can give it a name and description:








    Click on Export filter and Dirac takes a few seconds to upload the filter:








    Once uploaded, I can navigate to JRiver where I have the DLP VST loaded and enabled:








    It is recommended to leave the delay and gain compensation on. I also adjusted the gain slider to about -6 dB for headroom management. The meters will peak red if there is any clipping, which I experienced none. I could probably go to 3 dB of headroom management, but I have plenty of power on tap.


    OK, now listening to music! But before I comment on the sound, I also wanted to try a partial correction to 600 Hz as can be seen as a foreshadow in slot 2 ☺



    Partial Correction


    I can go back to my saved measurements, don’t forget to save!








    And back to the filter design section. Creating a partial correction is dead easy. All I need to do is grab the right marker that was previously at 22.1 kHz and drag the marker to the left to about 600 Hz:









    So the frequencies between 25.7 Hz and 587 Hz will be corrected and the rest left alone. Note, if I were using Dirac and Digital Room Correction for the first time, this is where I would suggest starting with a partial correction. This way one can focus your attention on just listening for an improved bass response and not a change in overall frequency response. 


    We proceed to filter export and load the filter into the 2nd slot:








    As one can see, I have several filter designs loaded, but here we are focused on the partial correction.


    Let’s move on to the sofa, wide imaging measurements.


    Sofa Wide Imaging







    After you have selected Sofa and Wide imaging, proceed to take the measurements:








    In this screen shot, I am on my last of 17 measurements. 3 sweeps per measurement times 17 measurements = 51 sweeps. Whew, that’s a lot and took me about 15 minutes to get through them all. I did not use a measuring tape. I just took a guess as to where the mic should go at each location, either raising or dropping the mic height and placing the mic at the front or back of my sofa, which I have temporarily moved out of the way. Note these 17 measurements covered a 6ft wide x 2ft deep x 2ft of height variability where my couch is.


    At any time you can re measure a position. Again we proceed to filter design. I just used the same default target as before and then switching to the corrected filter response:








    The response is so smooth I need to have a look without the target obscuring the correction:








    Wowser! That’s based on 17 measurements around my three seat couch area. To give an idea of all of the responses around the area, Dirac has a “spread” feature that allows you to see this if you check the box in the lower right hand:







    Those are 17 measurements made of left and right channels at the various locations around my 6’ x 2’ couch area. One can see the variability of the measurements based on position and again, by about 500 Hz, there is less variability as the loudspeaker is in control of the frequency response and not so much the room.


    Switching the view to impulse response:







    The corrected impulse is on the left and measured impulse on the right. As one can see on the left, the impulse or transient response is a cleaned up version of the measurement. Vertical scale is amplitude and horizontal scale in milliseconds. 


    The big vertical spike is the direct sound from the loudspeaker arriving at the microphone without any reflections. The smaller spikes, after the direct sound are early reflections. The corrected impulse response shows a clean spike and very little spikes (i.e. early reflections) after. 


    Sound travels roughly 1 foot per millisecond, so it becomes easier to understand that right after the direct sound, are the reflections (i.e. diffraction) off the speaker cabinet and then the speaker stand and anything else nearby like floor bounce or front/side wall bounce or ceiling bounce, all of those reflections are contributing to the sound, after the direct sound and our ears have a pattern to integrate those early reflections (i.e. the Haas effect) and understand amplitude and frequency response.


    It is a complicated topic as it involves so many aspects of why we hear what we hear in small room acoustics; standing waves, room resonances, early reflections, later reflections, room ratios, room construction and treatments, digital filtering, FIR, IIR, our ears non-linear response to both amplitude and frequency response, the Haas Effect, which reflections are good, which are bad, and on it goes.


    At this stage, I just wanted to show that Dirac works in the time domain. Given multiple measurement locations, one can understand that the sound and reflections arrive at different times and in different ways depending on the mic location relative to the loudspeakers. Using the concept of superposition and what we know about the physics of how standing waves respond in a rooms, we can work out the pattern and therefore correct for a wider sweet spot, which is what the 17 measurements are about. Dirac knows the phase relationships between the measurements plus taking the speakers as a pair into account, is used to calculate the correction filter.


    A note about target curves. While I have been using Dirac’s suggested target curve based on the measurements, you are free to create your own target curves. As mentioned above in the Subjective and Objective Evaluation of Room Correction products, the most preferred or accurate or neutral response is one that is 20 Hz to about -8 or -9 dB at 20 kHz. 


    Here I have dialed that in the target curve by grabbing the control points of the target and dragging them down a bit to get the desired target response. Of course, one can add and delete control points along the target (right click on the target). One can also save and load targets from the menu at the top left, beside the help icon.


    I was able to catch Dirac’s old correction computation as it was calculating the new correction along the new target:








    You can see how much I pulled down the target. It is not a lot, but is an audible difference. Just my personal preference. Of course, export to DLP and start listening:







    I have 7 of the 8 slots filled with a variety of filters to listen to. Before we get to the subjective listening section, here are a couple of “spot” verification measurements I made with REW.



    REW Verification Measurements


    This is just a “spot” verification of the correction. It is a loopback measurement where I am feeding the digital output of REW sweep test tone into the JRiver’s ASIO digital line input and it passing through Dirac Live Processor with the correction engaged and fed out my Hilo DAC to the Purifi amp and speakers, picked up by the measurement mic, through a mic preamp, Hilo ADC and routed to REW’s digital input. Then the measurement can be displayed in a variety of graphs to look at different viewpoints of the acoustic measurement of the room and loudspeakers. This is not a “gated” measurement as we do want the room’s low frequencies in the picture and using REW’s default impulse window of 500 milliseconds.


    One should note that this is not fully representative as it is one measurement made at the middle listening position. Ideally, I would take 17 measurements at the same or similar locations as I did in Dirac and vector average them in REW. And even then it still will not be quite the same as Dirac is applying more than just a vector average. However, it does verify that Dirac is doing what it is supposed to do:







    On the top are the Purifi SPK4 speakers measured at the listening position from my previous article and the bottom with the Dirac correction enabled. The speakers are in a 9ft equilateral triangle. I just split the screens apart to make it an easier comparison. Let’s start with the low frequency response and work our way up to the high frequencies, calling out the differences.


    Dirac was able to extend the low end frequency response in my room to below 30 Hz. -3 dB down at 22 Hz for the left speaker (as it is more in the corner of the room) and 28 Hz for the right speaker, as it is almost center in the room and does not get the corner boundary reinforcement. Compare that to -3 dB down at 32 Hz on the left and 45 Hz for the right speaker without correction.


    Looking at the 30 Hz to 60 Hz region on the correction, both speakers are matched closer together in amplitude response for a more solid bass response. This is in addition to being smoother and less peaky at 36 Hz for the left uncorrected speaker and 55 Hz for the right uncorrected speaker. Remember, our ears follow the “envelope” of the frequency response with our ears more attuned to peaks rather than narrow dips in frequency response.


    The big correction comes at 80 and 90 Hz as one can see in the uncorrected response. The total swing from the lowest point at 90 Hz to the highest point at 110 Hz is 23 dB. To our ears, a bass note playing at 90 Hz will be ¼ as loud as compared to a bass note at 110 Hz and vice versa. I.e. a bass note at 110 Hz will sound 4 times as loud as compared to the bass note at 90 Hz. This is classic room modes and we all got em, albeit at different frequencies dependent on one’s room ratio. While the dip is still there, it has been reduced by over 50% to ±5 dB which is very close to studio tolerance of ±3 dB. I suspect it would be in this range if I vector averaged 17 measurements in REW. Good enough for a spot check.


    Note Dirac pulls downs the peaks at 234 Hz, 461 Hz and 1.2 kHz. We also see a smoother response from 2 kHz to 5 kHz which just pulls down the brightness of the AMT tweeter just a bit. Finally, we extend the response a bit past 10 kHz. From good to great goes the speaker’s in-room frequency response, not only smoother but extended on both ends of the frequency spectrum.


    Let’s look at the timing or step response. Dirac makes a claim that “misaligned drivers in multi-way loudspeakers can be corrected by automatically applying different delays to different frequency ranges.” So let’s verify this claim by first looking at the step response of the uncorrected Purifi SPK4:








    So the spike (doublet) at time 0ms on the horizontal scale is the AMT tweeter and the negative going portion is perfectly blended into the start of Purifi’s PTT6.5 woofer. Classic or “textbook” passive crossover design. However, not truly time aligned. 


    Let’s look at the corrected response:








    Here we see the drivers are perfectly time aligned with the straight vertical “step” as both drivers response are arriving at your ears at the same time. Claim verified. There is just a hint of preringing at the beginning of the step response. I know it is not audible, as I have experimented in detail with greatly exaggerated preringing examples in my book, “Accurate Sound Reproduction using DSP.” Completely innocuous with the main goal of time alignment of drivers achieved.


    While phase and time alignment are not supposed to be audible, in my listening tests I have performed over the years, they are to my ears. Excess phase correction in the low frequency response is audible to my ears as is time alignment of drivers. Perhaps a future article on more discussion around this, but suffice to say, Dirac is doing its job in the time domain.



    Subjective Listening





    Note the dual Rythmik F18 subs were not used in the evaluation. I did have to check a couple of times as the amount of sub 30 Hz output from the Purifi’s PTT6.5” (sub)woofer is astonishing. However, I do intend to use the subs in Part 2 of using Dirac Live Bass Management in an upcoming review.


    The first thing I wanted to try was use my reference bass recording, Madonna’s, “Power of Goodbye” to test out Dirac’s partial correction up to 600 Hz in my room.


    image34.jpgThe reason I like using this recording for testing bass frequencies is because it has long sustained bass notes. This makes it easier to hear the room’s resonances. As expected, there are some bass notes that practically disappear and other bass notes that dominate the sound in my room.


    Enabling Dirac brings the level of bass notes to the same amplitude and the bass response is solid and powerful on each sustained note. It is still amazing to me as when I was working in recording studio control rooms, the only way to control room modes was the geometric and acoustic design of the control room. Aside from the room controlling reflections and acoustic treatments, the bass traps required to deal with very low frequencies at long wavelengths meant for a special acoustic design: a room within a room. The bass would pass through the shell of the inner room and be “trapped” in the outer shell so as not to pass back into the inner room. You can imagine the construction costs. Now at the flick of a digital switch, for truly a fraction of the cost, one can have the same smooth solid bass response at every frequency. What a time to be alive!


    image36.jpgAnother fav track I have for listening to bass evenness is Rebecca Pidgeon’s “Spanish Harlem”. A very nice Bob Katz recording and master of an acoustic bass guitar, in addition to Rebecca’s wonderful vocal rendition. Spanish Harlem, in the key of G, uses the classic 1, 4, 5 progression. Here are the frequencies of the fundamental notes of the bass:




    So without Dirac enabled, the 62 Hz to 82 Hz range of bass notes are really down in sound pressure level and the 110 Hz bass note literally sounds like a “coke bottle” resonance it is so loud and dominating in my room. 


    Enabling Dirac, brings back the proper level balance in the low end where each bass note is heard succinctly and even in level. When your ears starting tuning in, it really becomes apparent the differences. Having nice solid, even sounding bass arriving at your ears is a real treat. The reason why I say our ears need to tune in is because we are so used to listening to uneven bass, we are simply used to it and don’t give it a second thought. Remember JJ’s presentation. But once you hear how smooth it can be with your existing loudspeakers in your room, it is impossible to go back. Just the ability to smooth out the bass response is well worth the price of the software, aside from the additional benefits we are about to discuss.


    Let’s try the full range correction, but for the single seat. I find it a great boon being able to switch on and off DLP while listening in real time. There is no delay or interruption of sound or glitches of any sort, just a smooth and transparent switch. This makes is really easy to compare uncorrected to corrected or comparing different correction filters. This makes it easy to hear the differences instantly and then appreciate them over a period of time.


    image37.jpgSRV and Double Trouble’s, “Tin Pan Alley” is one of my favorite blues recordings. It was the first song and first take of the recording for the album that captured the feeling so well. When I was recording, I was always trying to get bands to “practice” before we recorded, but I was secretly recording as invariably the first take is sometimes the best take. Case in point this tune, wow!


    Great dynamic range that pulses with the emotion of the song. Great bass line that sounds nice and smooth with Dirac enabled. 


    But what really stood out for me is the Stevie’s strat sound with the Fender Leslie Vibrotone giving it that rotating stereo effect. It sounds so clear and precise with Dirac enabled, almost spooky hearing SRV fingers sliding up and down the strings with the Leslie effect enabled. Goosebumps territory.


    I switched over to the sofa, wide imaging corrections and re-listened to the above tracks, switching from single seat to wide imaging, at the same time moving around on my couch. I wanted to see if the 5 measurements versus 17 measurements were audible in some way to my ears. I found the changes to be subtle with the 17 measurements offering a bit more clarity in the overall sound, especially moving to edges of my couch area. I must say the phantom center image was perfect between the speakers, no wandering of the center image versus frequency. Excellent spatial imaging with a 3D depth of field I only hear from speakers that are time aligned with both channels closely matching in frequency response.


    Even with the 5 measurements, Dirac’s room correction algorithm appears to be quite robust and does not require an overabundance of measurements to get good even bass and smooth overall frequency response. While I enjoyed the benefits of partial correction, my preference is for the full range correction in two areas. One advantage was smoothing any midrange and high frequency “peaks” which with the Purifi SPK4 demo kit were small, but makes a difference not only in the smoothness of the sound, but also the vocals and instruments in the midrange “sat” in the overall mix where I thought they should be rather than sitting in front of the mix being a bit forward in sound from 2 kHz to 5 kHz region.


    Finally, I like the full range correction as I can dial in a preferred target of simply what I am used to listening to. Personally, I find most speakers sound too “bright” to my ears and confirmed by my measurements. While I have performed some speaker reviews here on Audiophile Style, I have had many pass through my listening room and all too bright for my tastes. The only one that had the preferred response out of the box is the Dutch and Dutch 8c. The KEF LS50 a very close 2nd, but just voiced a little too bright in the 2 kHz range, but Dirac would do a nice job of toning that back just a bit. Maybe we will see that in a future article.





    Well folks, it is 2020 and if you are not using digital room correction, at least partial correction to smooth the bass frequencies in your listening room, you are missing out on a simple but audible optimization. At a retail price of US $349, coupled with a US $100 calibrated measurement mic like the UMIK-1, this is a “no brainer” upgrade to your existing system that is both measureable and audible in a positive way. For existing Dirac 1.x customers, it is a free upgrade. In fact, while I am biased towards advanced DSP room correction, I know of no other way to achieve this level of sonic improvement for dollars spent.


    Dirac 2 has made the process of applying room correction as simple as possible. Setup the mic, take measurements and click next, next, next, through the wizard and be listening to the smooth bass tones in the shortest time possible. They have made it difficult for anyone to mess up ☺ 


    It is interesting that Dirac chose the VST plugin route, but I can see that their market is not only audiophiles but also the semi/Pro audio market as virtually every Digital Audio Workstation (DAW) uses Steinberg’s VST software plugin architecture. Dirac also provides AU and AAX plugins for Mac users and for DAW’s that use that plugin architecture like ProTools. You can find Dirac Live on the largest marketplace for plugins at KVRAudio.


    I have all but given up going to audio shows due to the fact that below the (hotel) room’s transition frequency, the room dominates the bass response regardless of the type of or how expensive the loudspeakers used are. As Floyd Toole’s research shows that bass subjectively accounts for 30% of how we judge speakers sound quality. And “ANY loudspeaker can sound better after room EQ, so long as it competently addresses the bass frequencies - this is not a guarantee, but really is not difficult for at least the prime listener” In the case of Dirac, the sofa, wide imaging selection extends the bass sweet spot across at least three seats. 


    To answer the inevitable question, which sounds better, Acourate, Audiolense or Dirac, since I have evaluated all three. I will say they all improve the low frequency response of virtually any system in any room. One can model the “ideal” loudspeaker in an “ideal” room and then it is a matter of which room reflections and how many are positive for the sound quality and how many are not, are taken care of. There is significant scientific research on this topic and with quite a bit of agreement. Having said that, all three DSP room correction software employ different strategies to arrive at the “ideal” result. In the case of Dirac, if you are looking for the shortest path to the result, this is it. That’s also a limitation. Other than different target responses, everything else is pretty much closed off and taken care for you with no user adjustable controls. 


    I did not try Dirac 1.x, so have no way of comparing other than reading through the Dirac 1.x 42 page manual. I must say Dirac has greatly simplified the use of their room correction software for Dirac 2. I did not have to open a manual, I just started using it. I found the improvements made to my loudspeakers in my room by Dirac were audible to my ears and measurable in a positive way. Recommended.






    image38.jpegMitch “Mitchco” Barnett.


    I love music and audio. I grew up with music around me, as my mom was a piano player (swing) and my dad was an audiophile (jazz). My hobby is building speakers, amps, preamps, etc., and I still DIY today.

    I mixed live sound for a variety of bands, which led to working full-time in multiple 24-track recording studios. Over 10 years, I recorded, mixed, and sometimes produced over 30 albums. I wrote a book on, “Accurate Sound Reproduction using DSP” and run an Accurate Sound Calibration service.

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    Awesome Job!! Been searching for A/B article with Dirac and REW to compare results are legit.  Now trying to Figure out best way to implement Dirac with streaming Qobuz.  Roon? NAD C658,  or there a way with using $349 route using my laptop?

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    Complete noob here and was fascinated by your article! You have corrected your sound without the subs connected I believe. I have a 2.2 system (KEF LS50 & REL T9i) how would I do this as I believe the subs have a massive effect on the room sound? I use ROON ROCK on a NUK8i7.

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    8 hours ago, flak said:


    Excellent... thorough and knowledgeable review as expected from mitchco!

    @sem115 one of the simple solutions for streaming Qobuz can be Audirvana that directly supports it (together wih other streaming services) and supports standard plugins as well

    Thanks guys for the info.  Great news since I already have Audirvana & Mic I use with REW. Excited to get Dirac next week and spend all weekend listening to music.  

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    Thanks for another great article! $349 sounds reasonable but what about a trial/evaluation to find out what it can do for my room+system? Do you know if that's available? I can't find anything on the Dirac web site.

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    Seems like a preview of the NAD Masters M33, which will feature the first mass-market implementation of Purifi amplification and built-in DiracLive.

    NAD Masters M33.jpg

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    Finally, some evidence of why Dirac is better than REW. Looks like I need to upgrade. 5 stars!


    I'm using REW with a miniDSP to integrate my subs. Anxiously looking forward to Part 2, Active Bass Management


    PS As per my PM message, I'm hoping you can review the miniDSP SHD. The SHD Studio is also very interesting.

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    I wonder why the corrected step response shows much more ringing than the uncorrected. As far as I can see it is at around 20kHz. Is it an artifact of Umik with step transitions (I see similar ringing just measuring my Wideband drivers using Umik) or is it introduced by the DSP?

    I understand digital speaker correction which is what basically Dirac is doing at higher frequencies but I can not understand how the interaction of bass frequencies with room modes can be corrected by just altering the woofer output (past a single point in space). So I am looking forward to learn more about active bass management!

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    18 hours ago, digitaldufferme said:

    Complete noob here and was fascinated by your article! You have corrected your sound without the subs connected I believe. I have a 2.2 system (KEF LS50 & REL T9i) how would I do this as I believe the subs have a massive effect on the room sound? I use ROON ROCK on a NUK8i7.


    Yes, I did not have the subs connected, but the the little Purifi's have solid output below 30 Hz. But my Rythmik dual F18's go down to 6 Hz in my room. How is your 2.2 system connected? Is it Y cabling or ?

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    10 hours ago, blue2 said:

    Thanks for another great article! $349 sounds reasonable but what about a trial/evaluation to find out what it can do for my room+system? Do you know if that's available? I can't find anything on the Dirac web site.

    Thanks! From: https://www.dirac.com/faq-general it looks the free trial is 14 days. Perhaps @flak can confirm...

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    6 hours ago, mitchco said:


    I did not use a UMIK-1 for this particular article, even though I do have one and have not come across any ringing artefacts with it yet. But I am going to test it out extensively in an upcoming article. As the speakers are also gone, I can't retest easily to confirm what the issue was. I could have goofed on my loopback test and resampled somewhere in the chain like 48 kHz signal through a 44.1 kHz filter. When I get a chance, I will confirm using another speaker/test, but given the amount of time I have spent on trying to identify (pre)ringing artefacts previously, it certainly inaudible to these ears. The main point I was trying to get across was the time alignment.


    Understanding room correction is complicated A separate article is required to get though it all and I am contemplating writing one. In a nutshell, good room correction software will take an acoustic measurement and extract the minimum phase response and since speakers are minimum phase devices, correcting the frequency response will also correct the phase response. However, that is only half the picture as there is the room to deal with, which is what Dirac calls mixed phase or others call it excess phase, which includes room resonances and reflections.


    And in the time domain, we know what the ideal speaker target is by looking at the timing (i.e. step) response of an "ideal" minimum phase speaker. So... the room correction software corrects the time domain to follow the ideal minimum phase target. You can see that if you have my book or some of the articles here at AS show that as well. But the trick is that this is wavelength dependant, so at low frequencies, the correction time window is long (like 600ms for example) and as frequency increases the correction time window becomes shorter so above the rooms transition frequency we are looking at more of the direct sound plus baffle of the speaker. Often called frequency dependant windowing. In other words, at low frequencies, the room correction software has a large time window that corrects both the direct sound and reflected sound (i.e. room resonance) towards a target response. At high frequencies, it is mostly the direct sound because if we tried to also correct for mid-range and high frequency comb filtering room reflections, the high frequency response of the loudspeaker sounds like a dentists drill. This is how one can hear "over correction" in the high frequencies.


    Hope that helps somewhat. Like I say, requires a separate article to fully explain.

    Thanks for your response, Toole and also in a similar version Geddes are proposing to use multiple subwoofers spaced over the room to allow wider zones of bass correction (with specific phase corrections). I wonder if that is something Dirac can do and if that leads to a significant improvement compared to standard 2 woofers/subwoofers? Of course that adds a lot of complexity to the setup both computational and room design wise. REW room simulator shows some benefits but I wonder how real these simulations are?

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    10 hours ago, mitchco said:


    Yes, I did not have the subs connected, but the the little Purifi's have solid output below 30 Hz. But my Rythmik dual F18's go down to 6 Hz in my room. How is your 2.2 system connected? Is it Y cabling or ?

    Following the advice of REL, I connect the left speaker and the left sub to one RCA output on the amp and the same for the right channel so that the REL T9i get a full range signal.

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    Thanks mitchco, always very useful your articles and reviews. I have been using Dirac 1.x since 2013 and lately I have been studying Audiolense and Acourate to try to have a (perhaps) better room correction by linearizing the speakers first, and after the room in the sweet spot..
    Do you think that a better result can be achieved than Dirac 2.0?

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    Hey @mitchco, for Part Two, can you please discuss integrating subs using ported vs. sealed speakers? 2nd-order vs. 4th-order monitor roll-off is a complicating factor.

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    16 hours ago, monteverdi said:

    Thanks for your response, Toole and also in a similar version Geddes are proposing to use multiple subwoofers spaced over the room to allow wider zones of bass correction (with specific phase corrections). I wonder if that is something Dirac can do and if that leads to a significant improvement compared to standard 2 woofers/subwoofers? Of course that adds a lot of complexity to the setup both computational and room design wise. REW room simulator shows some benefits but I wonder how real these simulations are?


    Yes, I have seen both Toole's, plus Todd Welti's presentation on multiple subs, and Earl's paper, plus Duke LeJeune's swarm system. All show positive benefit's but one still needs room correction to obtain the smoothest bass response based on experiments I have run with multiple subs and locations.


    Even if your sub(s) are part of your two channel system (i.e. not using digital XO), room correction is still a major benefit, which is what Dirac does. However, the new Dirac Bass Management will provide further control, but also requires more than 2 DAC channels.


    REW Room Simulator works very well and is quite accurate! Room mode calculators are mostly based on the physical dimensions of one's room. Room construction and rooms treatments (to a certain degree as most do little below 100 Hz) have an impact, but below the room's transition frequency, it is all about the room ratio. The reality is that no matter where the speakers/subs are placed in the room relative to the listening positions, there is no escaping room modes. All that happens is that the dips and peaks move in frequency based on these (super)positions. One can get lucky and minimize, so it is worth the effort. However, in the end, still need room eq...

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    7 hours ago, Zapuan said:
    Thanks mitchco, always very useful your articles and reviews. I have been using Dirac 1.x since 2013 and lately I have been studying Audiolense and Acourate to try to have a (perhaps) better room correction by linearizing the speakers first, and after the room in the sweet spot..
    Do you think that a better result can be achieved than Dirac 2.0?

    Cheers @Zapuan As mentioned in the review, I did not get a chance to try Dirac 1.x, but according to the manufacturer, there are several improvements upgrading to D2. As I understand it, you are entitled to a free upgrade and given the simplified measurement process, it is worth a shot to try first 🙂

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    14 hours ago, digitaldufferme said:

    Following the advice of REL, I connect the left speaker and the left sub to one RCA output on the amp and the same for the right channel so that the REL T9i get a full range signal.


    There is no reason why this would not work with Dirac. When the free trial is available, you might want to give it a try. The only issue is that Roon does not support VST plugin's at this time. So you would need to temporally try it in a different music player that supports VST plugins. Then at least you could ascertain the sonic benefit, which I think would be significant in your setup.

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    46 minutes ago, mitchco said:

    Saluti @Zapuan  Come menzionato nella recensione, non ho avuto la possibilità di provare Dirac 1.x, ma secondo il produttore, ci sono diversi miglioramenti che aggiornano a D2. A quanto ho capito, hai diritto a un aggiornamento gratuito e dato il processo di misurazione semplificato, vale la pena provare prima 🙂

    my question is whether in your opinion with Acourate or Audiolense you can achieve a better result than that obtainable with Dirac 2

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    A while back you reviewed the Dynaudio Focus 600XD and raved about this speaker. Additionally you discussed its step response and its importance. Would Dirac benefit this type of active speaker and in doing so, would the step response be compromised?

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