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Post by urwi on Dec 19, 2014 5:51:29 GMT -5
How does the XMC determine the correct crossover settings, delay and gain? Dirac treats the speaker as full range. BM is applied to the corrected signals. Tony |
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Post by ansat on Dec 19, 2014 9:11:34 GMT -5
How does the XMC determine the correct crossover settings, delay and gain? Dirac treats the speaker as full range. BM is applied to the corrected signals. Tony You decide the xover points gain and delay are controlled by dirac. Tony |
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Post by urwi on Dec 19, 2014 10:33:27 GMT -5
So speaker distance becomes part of the Dirac filter? What if you switch off Dirac, speaker distance would be off, no? Does Dirac honor the crossover points set or does it equalize the speaker response independently of crossover settings? You decide the xover points gain and delay are controlled by dirac. Tony |
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Post by ansat on Dec 19, 2014 10:52:13 GMT -5
So speaker distance becomes part of the Dirac filter? What if you switch off Dirac, speaker distance would be off, no? Does Dirac honor the crossover points set or does it equalize the speaker response independently of crossover settings? You decide the xover points gain and delay are controlled by dirac. Tony Dirac is independent of xover settings. To turn dirac off you have to select another speaker setup which you can set the delays manually. |
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Post by douglasssf on Dec 19, 2014 18:34:03 GMT -5
Flavio- Thanks for your input in this forum and in the miniDSP nanoAVR DL forum. I'm trying to get a basic grip on the starting-off case of "small" LCR/surrounds and a single subwoofer that handles both the LFE channel and the bass portion of the LCR/surround channels redirected to it by the receiver's bass management. I.e., a garden-variety 5.1 setup. Is the following a fair summary of how Dirac Live works on the XMC-1 for this configuration? 1. Dirac will properly correct the subwoofer's output (combined LFE plus BM-redirected signal) in the frequency domain, assuming BM was active during measurement and isn't changed afterwards. 2. Unless the subwoofer is physically close to the speakers whose low frequencies are being redirected to it by BM, Dirac will have a hard time correcting in the time domain, because each of the LCR/surround channels will be coming from two different locations--the higher frequencies from a "small" speaker and the lower frequencies from the subwoofer. If this fairly describes how Dirac Live works on the XMC-1, can you suggest a work-around for #2? Are there other Dirac Live implementations that time-correct the BM signal (or the combined LFE-plus-BM signal) as if it were a separate channel? The literature on the Datasat RS20i makes it sound like it might do that. Thanks. Dirac treats the speaker as full range. BM is applied to the corrected signals. Tony True enough, and I assume the frequency adjustments will work out fine. But I don't see how Dirac can time-correct a notional full-range speaker that's located in two different physical positions...at the subwoofer for the lows and at the channel-specific speaker for the mids and highs. |
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Post by lbrown105 on Dec 19, 2014 19:33:06 GMT -5
^ that is what I am trying to figure out. I guess I will understand better when I can try the XMC-1 version. In the two channel it was simple but here I would think it should level set and time align individual subs and then eq the combined sub response. Then running the LCR and surrounds making sure the xover integration is good and of course the rest of the range is multi phase corrected where needed.
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Post by ansat on Dec 20, 2014 11:20:04 GMT -5
Dirac treats the speaker as full range. BM is applied to the corrected signals. Tony True enough, and I assume the frequency adjustments will work out fine. But I don't see how Dirac can time-correct a notional full-range speaker that's located in two different physical positions...at the subwoofer for the lows and at the channel-specific speaker for the mids and highs. ^ that is what I am trying to figure out. I guess I will understand better when I can try the XMC-1 version. In the two channel it was simple but here I would think it should level set and time align individual subs and then eq the combined sub response. Then running the LCR and surrounds making sure the xover integration is good and of course the rest of the range is multi phase corrected where needed. All bass managment seems to be applied after dirac and is not tested. With multiple subwoofers, room correction could be designed to handle multiple subwoofers, but I have yet to see any do it right. The problem is that in a speaker array (2 or more speakers playing the same content) needs to be time adjusted to avoid cancelation. Then eq applied to both speakers so that its summed response is flat across the widest listening positions. Once finished, the xover needs to be tested on the lcr, and the summed response needs to be time adjusted to avoid cancelation at the xover point (the best you can). Sometimes it's best to move the xover point in this process to get good results across multiple speakers. Tony |
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Post by jking on Dec 22, 2014 6:07:49 GMT -5
True enough, and I assume the frequency adjustments will work out fine. But I don't see how Dirac can time-correct a notional full-range speaker that's located in two different physical positions...at the subwoofer for the lows and at the channel-specific speaker for the mids and highs. ^ that is what I am trying to figure out. I guess I will understand better when I can try the XMC-1 version. In the two channel it was simple but here I would think it should level set and time align individual subs and then eq the combined sub response. Then running the LCR and surrounds making sure the xover integration is good and of course the rest of the range is multi phase corrected where needed. All bass managment seems to be applied after dirac and is not tested. With multiple subwoofers, room correction could be designed to handle multiple subwoofers, but I have yet to see any do it right. The problem is that in a speaker array (2 or more speakers playing the same content) needs to be time adjusted to avoid cancelation. Then eq applied to both speakers so that its summed response is flat across the widest listening positions. Once finished, the xover needs to be tested on the lcr, and the summed response needs to be time adjusted to avoid cancelation at the xover point (the best you can). Sometimes it's best to move the xover point in this process to get good results across multiple speakers. Tony since my living room is not finished yet I have had to place my subs on opposing walls about 13 feet apart and facing each other not facing me. The subs are also about 1 foot forward of the main floor standing speakers which, are setup for stereo listening at 9 feet apart. This about as far from perfect a setup as you can get. So far the Dirac software has been able to flatten out the sound gurve without any problems. I have thrown different speaker set ups ( large , small with different crossover points) and found that the software has no problems fixing any of the problems I throw it. I just may break out my old B&W 650 sub and put it in the rear of the room and see what happens with 3 subs totally misplaced. Dirac Le so far does everything I asked of it. |
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Post by urwi on Dec 22, 2014 7:04:17 GMT -5
I do hope it's the other way around. If bass management is applied after equalization you might end up with unwanted interference effects. The correct way of doing it is to first apply bass management and then equalize the individual speaker channels. Dirac treats the speaker as full range. BM is applied to the corrected signals. Tony |
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Post by ansat on Dec 22, 2014 8:10:50 GMT -5
I do hope it's the other way around. If bass management is applied after equalization you might end up with unwanted interference effects. The correct way of doing it is to first apply bass management and then equalize the individual speaker channels. Dirac treats the speaker as full range. BM is applied to the corrected signals. Tony My solution was to use outboard delay and eq. With the arc that I have played with, I have come to the conclusion that I would rather keep multiple subwoofers under my own control. Tony |
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Post by jmilton on Dec 22, 2014 8:48:45 GMT -5
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Post by urwi on Dec 22, 2014 10:20:46 GMT -5
That's not what I've meant. If equalization is performed before bass management is applied then the signal will be distorted by the summing stage in bass management. The simple solution is to first apply bass management and then equalize the individual speaker feeds. So how does the XMC-1 handle this? My solution was to use outboard delay and eq. With the arc that I have played with, I have come to the conclusion that I would rather keep multiple subwoofers under my own control. Tony |
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Post by ansat on Dec 22, 2014 11:52:22 GMT -5
From my measurements and tests, Dirac creates a filter for each speaker. Dirac determines the usable frequency range and only creates a filter to address that portion. I am unsure if the BM and slope is applied before or after the filter in the xmc. BM is not applied during the filter creation. Also, it appears Dirac time aligns all speakers to a reference point and does not take into consideration the xover alignment or multiple subs played at the same time.
But the problems I have seen at the crossover points, are time alignment issues. I have had to shift the subs time alignment to eliminate the nulls at the xover points.
Tony
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Post by urwi on Dec 22, 2014 15:24:11 GMT -5
Pretty important to get this right. Measurements could show if the implementation is correct. I am unsure if the BM and slope is applied before or after the filter in the xmc. |
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Post by jking on Dec 24, 2014 8:00:23 GMT -5
This is a real good look into the Dirac System from the top Man in charge. Please note that they will be coming out with a Bass enhancement control maybe in 2015 \. Happy reading Copied from Audoholics
Dirac Room Correction Interview With Mathias Johansson
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by Steve Munz — November 05, 2014
The Emotiva XMC-1 features a custom version of Dirac Live. .
Like Audyssey MultEQ, Yamaha's YPAO, and Pioneer's MCACC, Dirac Live is a room correction system designed to counter the ill effects of placing loudspeakers in a real room. While we know Dirac's products are used on high end products like the Emotiva XMC-1 and Theta Digital Casablanca, we can't really claim to know all the fine details of how Dirac Live actually works. Fortunately, we know somebody that does: Mathias Johansson, CEO of Dirac. Of course, Mathias isn't just a business man; he's got a Ph.D. in Signal Processing. If you want to know the full scoop on Dirac Live, keep reading!
Audioholics: What kind of filters do your room correction products use, and at what resolution (i.e. 1/3 octave, 1/12 octave, etc.)?
Mathias Johansson: Dirac Live uses a proprietary structure that is neither plain FIR nor plain IIR. The downsides of using parametric filters (IIR) include that you are limited in resolution by the number of filters employed and they have inherent limitations in optimizing phase/impulse response properties of the loudspeaker. If you don’t have sufficient word lengths, you also get problems in maintaining the resolution in the bass region. FIR filters, on the other hand, are also limited but in slightly different ways: First, with a finite number of filter taps (FIR = Finite Impulse Response) you lose resolution in the low-frequency region. The high-frequency resolution may instead even be too high, unless you smooth your response by other means. Too high resolution seems like an oxymoron, but then don’t forget that a filter acts both in the frequency domain and in the time domain. If you do very detailed corrections in the high frequency region, you also introduce ringing in the time domain. That may not always be easily audible, but a typical artifact of too detailed high-frequency compensation is a more diffuse sound when you are using stereo or multi-channel systems. The reason is that the time-domain ringing on one channel is different from another channel, and then the sound becomes de-correlated. Second, they cost more to implement than IIR filters, that is, they require more CPU power. On the up side, an FIR part is required in order to do correction of the phase/impulse response properties of an acoustic system. FIRs are also less cumbersome to implement than IIRs, as they are non-recursive and therefore less susceptible to round-off errors, etc.
Dirac’s solution is to use the best of the FIR filter (mixed-phase correction, i.e. time-domain correction) and IIR’s for what they are best at. Dirac Live does not simply use an FIR in cascade with a number of IIR sections, but a more complicated structure. The result is that our filter resolution is not limited by the filter structure, but by the measured properties of the acoustic environment. In essence, by using multiple measurements you can find the optimum resolution that does not lead to overcompensation. In a small listening area, you can do more detailed correction than in a large listening area.
Audioholics: What is the maximum boost / cut your room correction products will apply? Is it possible for users to set a limit in this respect (i.e. no more than 3dB of boost)?
Dirac’s solution is to use the best of the FIR filter (mixed-phase correction, i.e. time-domain correction) and IIR’s
Mathias Johansson: Normally, Dirac Live does not allow you to boost more than 10 dB. You can lower this by adjusting the target curve. However, narrow dips (nulls) are never compensated, as they are always position dependent in real acoustic spaces.
Audioholics: How do your room correction products help to address the typical issues a room causes (resonances, modal peaks/nulls, etc.)? Does room correction largely negate the need for room treatments for consumers, or would you suggest using both room correction and physical treatments?
Mathias Johansson: No room correction system negates the need for room treatments. What makes Dirac Live different from other systems that we have tested is how we make use of many measurement points to be able to do the best optimization of time-domain and frequency-domain properties. It is important to understand that only by using multiple measurements is it possible to understand the large differences in the response in the room, and thus to make the best optimization and compromise between different measurements. For example, making a time-domain optimization based on a single measurement in a reverberant room is a very bad idea as the impulse response varies so much from one position to another. With a single measurement you will always be guessing what happens in other positions. Room acoustics is cruel. Just inches away, the correlation drops so much you can’t infer what happens just based on one measurement. Only by using several measurements is it possible to get enough information to make a good correction which does not imply pre-ringing or de-correlation just inches away (and don’t forget that we have two ears. Just inches apart…) See the images below to understand some of the difficulties faced in making a good tuning of a speaker to a room.
This picture below shows 64 different measurement points in a room (one loudspeaker only). You might think that you don’t care about the results in that many points. Correct, but then you should be aware that these measurements were taken in an area spanning a very small volume of only 0.3 by 0.3 by 0.3 meter in the normal listening position of a chair! If you would just pick one of these measurement positions, you would be very lucky to get anything near the average (bold) line below. And if you are not that lucky, your “correction” will only improve some aspects, and actually deteriorate others.
Image 1
Here is another image. It shows impulse responses from 9 different measurement positions within the sweet spot of a very well damped room using Genelec monitors. The impulse responses have been time-aligned here to make them easier to compare. For reference, we show how the same impulse responses look after application of a Dirac Live filter and another filter with identical magnitude response but no phase correction (a so called minimum phase filter)
Image 2
Our approach gives an optimal compromise between multiple measurement positions, both in the frequency domain and in the time domain. Out of the room correction systems that we have been able to test so far, no other system yields a time-domain correction which is useful for many positions (for example, two ears). From the multiple measurements, we infer which time-domain and frequency-domain properties are common to all measurements, and therefore can be robustly compensated. In mathematical terms, we can derive the optimum filter by evaluating how the poles and zeros of different measurement positions are clustered. It is a cautious strategy in line with the maxim that we should optimize as much as we can, but not more.
Most other room correction systems are minimum-phase, which means that they try to not add any time-domain distortion, whereas Dirac Live actually reduces time-domain distortion. The results are audible in terms of imaging, clarity and bass tightness.
Digital room correction cannot change the response variations across different listening positions. This is where room treatments help tremendously, as they eliminate the reflections, etc, that cause acoustic variations across the room. However, Dirac recently showed a preview of an altogether different kind of digital room correction, which we prefer to call active room treatment. This approach, which we have named Dirac Unison, aims not just to combat average room behavior, but also changes the whole wave pattern in the room. This is accomplished by using multiple speakers. For example, if you are listening to stereo material on a 5.1 speaker set-up, Dirac Unison can use the remaining speakers to actively treat the room, rather than just do a virtual surround up-mix or simply shut them off. A speaker may be a primary source or a support source. The support sources are used to improve the impulse responses and frequency responses of the primary sources in all measurement positions. This way, we can control the wave pattern in the room, and speakers in corners start acting as bass traps, etc. We showcased this system at CES 2014, but we have not yet launched it commercially within HiFi. The first commercial system with Dirac Unison will actually be the brand new Volvo XC90 with a B&W loudspeaker set-up. In premium car audio systems, you may have up to 20 speakers and beyond. Without Dirac Unison as a ”conductor” that makes them play in perfect synch, it is very difficult to make that many speakers act coherently as a team.
Audioholics: Do your room correction products utilize multi-point measurements? Why or why not? If so, how many measurement points are available?
Mathias Johansson: Please see above. We recommend 9 measurement positions spread out in the listening region as randomly as possible, to capture all relevant sound field variations. In large listening venues such as cinemas, we of course use more measurements.
Audioholics: Do your room correction products correct subwoofer response? How do your products calibrate and correct the response of multiple subwoofers? Please describe the benefits of your method.
Mathias Johansson: Yes, we correct subwoofers. Regardless of the number of subwoofers, one of the main benefits of Dirac Live is the time-domain optimization. A lot of room acoustic behavior is non-minimum-phase and only a proper mixed-phase correction using multiple measurements can maximize the tightness of the bass.
It should be mentioned that the coming Dirac Unison technology will improve first and foremost the bass interaction of multiple-woofer systems through its unique joint time-domain optimization of all speakers. The first launch for the HiFi segment is not yet scheduled firmly, but will likely happen in 2015.
We recommend 9 measurement positions spread out in the listening region as randomly as possible
Audioholics: What is the default frequency range corrections are applied to? In other words, is there a frequency ceiling or floor above/below which correction isn't applied? If correction isn't applied full band, please explain.
Mathias Johansson: Dirac Live RCS uses a full-band correction as a default. We however offer the user a low-frequency limit and a high-frequency limit if the user wants to compensate only a certain frequency region. We have just started offering a ”bass-only” version of Dirac Live, which applies correction below 500 Hz only. But you can still adjust the target curve freely within that range.
Audioholics: Does your room correction software show users "before", "target", and "after" response curves? Is it possible for end users to adjust the final response curve such that they can flavor the sound to taste?
Mathias Johansson: Yes. We also suggest a target curve, and the user can change the response by simply editing the curve.
To continue our investigation of the various room correction products on the market, we got in touch with Mathias Johansson of Dirac who was kind enough to answer a few questions. For those unfamiliar with the company, their room correction solution is used commercially (i.e. in cinemas, recording studios, etc.) as well as in home audio products like the Theta Digital Casablanca and Emotiva XMC-1. Want to know the details of how Dirac Live works its magic? Keep reading!
Audioholics: What do you feel are the important differentiators between your room correction solution and competitors?
Mathias Johansson:
1. Correctly accounting for the spatial domain, that is, variations between the ears and between listening positions.
2. Working time-domain optimization that improves imaging, clarity and bass tightness
3. Compatibility when listening from a computer. Our ”virtual soundcard” processes all sound output from your computer, not just certain music software.
4. User friendliness. Advanced technology does not have to be difficult to use.
Audioholics: Does your room correction software run on an AVR/Pre-Pro or require an external computer for processing? If it requires an extra computer, what platform(s) does it run on? Can consumers purchase your solution as a stand-alone product/solution or only bundled as part of an AVR/pre-pro?
Mathias Johansson: Dirac Live Calibration Tool, which is used for taking measurements and creating the filters, run on Mac and Windows. To process sound, the Dirac Audio Processor, processes all sound output from the computer and acts just like a normal sound card. Sonic Studio also offers a version of Amarra that has built-in Dirac Live support up to 384 kHz.
Dirac Live RCS can create as many presets as you like.
There are a number of hardware units that use Dirac Live. These include Datasat RS20i, AP20 (for professional cinema), Theta Digital Casablanca, Emotiva XMC1, and the MiniDSP Dirac series. Users include broadcasting stations such as Swedish Radio, cinemas across the world, music producers, studio engineers, artists, as well as a wide variety of HiFi and home theater enthusiasts. You don’t have to be a professor to understand how to use Dirac Live or enjoy the benefits of a time-domain correction.
Dirac Live Suite
Dirac is available as a software solution for your computer in addition to being integrated on a variety of hardware units.
Audioholics: Do users have the ability to set multiple profiles--for example, setting a separate "music" and "movie" room correction profile where one can be tailored for a different frequency response range, bass response, different crossovers, etc?
Mathias Johansson: Yes. The number of presets depends on the particular hardware implementation. For Dirac Live RCS you can create as many presets as you like.
Acknowledgements
We'd like to thank to Dr. Johansson for sharing his insights on Dirac Live with us.
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Post by bolle on Jan 22, 2017 13:07:58 GMT -5
Was this actually ever tested how bass management and DIRAC interact in the XMC-1?
There are 2 possibilities:
1. DIRAC corrects speakers and sub. Bass management happens before the DIRAC filters are applied, so the sub gets the correct filters applied to the LFE and the redirected bass.
2. DIRAC corrects speakers and LFE. Bass management happens after the DIRAC filters are applied, so the sub gets a mix of different filters depending on if it is playing back LFE or redirected bass.
1. would be correct, 2. would be wrong. Actually 2 is the way DIRAC is currently implemented in the ARCAM products... How is it in the XMC-1?
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Post by ansat on Jan 22, 2017 13:34:50 GMT -5
Was this actually ever tested how bass management and DIRAC interact in the XMC-1? There are 2 possibilities: 1. DIRAC corrects speakers and sub. Bass management happens before the DIRAC filters are applied, so the sub gets the correct filters applied to the LFE and the redirected bass. 2. DIRAC corrects speakers and LFE. Bass management happens after the DIRAC filters are applied, so the sub gets a mix of different filters depending on if it is playing back LFE or redirected bass. 1. would be correct, 2. would be wrong. Actually 2 is the way DIRAC is currently implemented in the ARCAM products... How is it in the XMC-1? I did test this 2 years ago using rew, and taking measurements at the output of the xmc, for the life of me i cannot remember the details though. I want to say that #2 was what i found. But i would have to repeat the testing to be sure. T. |
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Post by bolle on Jan 22, 2017 13:37:29 GMT -5
Thank you for the answer! I can test this myself, just was curious if it has been done already.
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Post by urwi on Jan 23, 2017 16:42:28 GMT -5
Say it ain't so. Can't believe such a major bug would go unnoticed for years! Was this actually ever tested how bass management and DIRAC interact in the XMC-1? There are 2 possibilities: 1. DIRAC corrects speakers and sub. Bass management happens before the DIRAC filters are applied, so the sub gets the correct filters applied to the LFE and the redirected bass. 2. DIRAC corrects speakers and LFE. Bass management happens after the DIRAC filters are applied, so the sub gets a mix of different filters depending on if it is playing back LFE or redirected bass. 1. would be correct, 2. would be wrong. Actually 2 is the way DIRAC is currently implemented in the ARCAM products... How is it in the XMC-1? I did test this 2 years ago using rew, and taking measurements at the output of the xmc, for the life of me i cannot remember the details though. I want to say that #2 was what i found. But i would have to repeat the testing to be sure. T. |
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Post by bolle on Jan 24, 2017 5:06:12 GMT -5
I will measure on the weekend. Just asked because a user in a german home-cinema board stumpled upon the fact that it is the same problem in the new ARCAM devices using DIRAC... They also do bass management AFTER Dirac.
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Dirac treats the speaker as full range. BM is applied to the corrected signals.
