Every AV receiver does have room correction on board with which you can personalize the sound for your room. Still, Dirac technology claims to achieve a much better result. Arcam and NAD have already convinced them. But why would Dirac be superior?
Home cinema fans have been able to apply room correction with their AV receiver for years, via systems such as AccuEQ (Onkyo), Audyssey (Denon) and YPAO (Yamaha). Even the cheapest receiver has some form of correction built in. Recently you hear more and more in the home cinema world the name ‘Dirac’, referring to a system from Sweden. Arcam is one of the larger audio brands that it has recently started using in a number of devices, including the AVR550 and AVR850, and NAD will soon also start with Dirac. Why is there this sudden interest in technology now? And what makes it better than the other systems?
Dirac technology- why room correction?
The presence of correction software in an AV receiver is not that strange. The characteristics of the room have a significant influence on what you hear. And by ‘significant’ we really mean ‘very important’. A room can make a great speaker sound completely different and worse. Unfortunately, it almost never happens that the room can make up for a bad speaker.
The influence of the room is certainly noticeable if you place a surround setup in a living room. The placement of the speakers is almost always suboptimal in this situation. Dolby, for example, would like you to place the surround speakers at a certain angle behind you, but you cannot do that because the sofa is placed against a wall. It is a haphazard but common situation. In addition, a typical living room always has acoustic problems: the room is too small for the desired bass reproduction, there is reflection from the windows, the tiled floor makes everything sound bright, or one of the many other problems. The speakers themselves can also cause problems.
To discover what is different about Dirac, we went to two training days given by Arcam, one of the brands that use Dirac. At the invitation of Transtel-Sabima, the Belgian importer of Arcam, we visited the Cambridge offices for a first session, followed by advanced training for dealers and installers given at Alpha High End in Brasschaat, close to the Dutch border.
Many room correction systems on AV receivers work around the frequency response and volume levels, in particular to address so-called ‘room modes’ – problems with specific bass frequencies in your room – and to ensure that speakers that are not perfectly arranged still sound good in the listening position. . However, Dirac works on three fronts: frequency, phase and impulse response. The first and the last mainly have to do with room properties, but the fact that you can manipulate the phase is very special.
Optimize the speaker
Dirac applies so-called mixed phase filters, with which it tackles phase problems of your speakers itself. These are phase problems that occur between the different drivers of each speaker. Optimizing the drives at the speaker level is something that an AV receiver calibration system usually doesn’t do. At most, they check whether the speakers are in phase with each other.
No matter how good a speaker designer is, according to Dirac, perfect integration between all drivers in a speaker is impossible. In other words, it is very difficult to make sure that the tweeter, midrange driver and woofers are really in sync. “When you buy a speaker, you should really go for a model with an inert, vibration-free housing and drivers that respond very quickly,” notes Arcam product manager and teacher Andy Moore during the Advanced training.
The Dirac software is a black box at this point. Where after the measurement you can still adjust the frequency curve and view the impulse response, you will not see the phase adjustments.
Frequency
The two other domains that Dirac technology manipulates are the frequency and the impulse response. Just a word of explanation: if music or a movie soundtrack comes from your speakers, you will not hear the ‘pure’ sound in the seat. It may well be that your high-performance speakers still sound very dull, for example because high frequencies are absorbed by excessive attenuation. If you cover all the walls with a thick velvet curtain and put a fleecy carpet, you will get this result.
There is no life in it. It may also be that certain low frequencies are amplified throughout the room, causing them to dominate. Basses can sound very booming, with little detail and very woolly. This can happen, for example, if your listening chair is close to the back wall, so that you can get a kind of amplification of certain frequencies (boundary gain). Tile floors that strongly reflect high frequencies can in turn produce a very sharp and thin sound. As you can see, a lot can happen to sound in a room. Sometimes subtle, sometimes very drastic. In a later article on room effects, we will discuss this further.
Back to Dirac technology. Most systems implement Dirac Live, where you can intervene over the entire frequency response. There are also ‘light’ or basic versions of Dirac, which only intervene on the low frequencies below 500 Hz. That in itself is very powerful, because it is in this frequency range that room effects occur most strongly. Here you have to tackle standing waves and so-called ‘room modes’. These can be recognized in the measurement as extreme peaks and troughs.
Above 500-700 Hz deviations are also possible, for example due to reflection. However, intervening here is dangerous, Moore believes, and we can confirm that based on our own experiences. Adjusting the mid frequencies may mean that you just take away the ‘voicing’ or the unique sound from your speaker. And let the voicing be the reason why you chose that Bowers & Wilkins / Focal / Monitor Audio / Dali / fill-in-your-own-favorite-brand.
Impulse
The last domain where Dirac intervenes is the impulse response. In short, you could say that this is the speed of a speaker. With a sudden sound – a slap in the hand, a string strike, a kick drum – a loudspeaker has to do something difficult. From a standstill the driver suddenly has to move air and just after the peak it has to come to a stop again. It should not vibrate afterwards, because then it all becomes less exact and natural. Detail disappears because the driver is still working on the previous sound. The fact that drivers do not perfectly reproduce an impulse / tone is due to physics. Compare it with a car: it does not suddenly drive 100 km / h from a standstill. A certain amount of acceleration is required, and the same is true with braking. A driver cannot suddenly make his maximum movement and then stop.
Also keep in mind that a loudspeaker rarely needs to produce just one tone. In a hellish guitar solo by Metallica the notes follow each other very quickly. The better the impulse response, the smoother and more immersive that finger play becomes. Impulse response is also crucial for subwoofers, because the faster a woofer starts and then comes to a stop, the tighter the bass.
Where can you find it?
As mentioned, you will find Dirac technology at Arcam (the AVR390, AVR550 and AVR850 AV receivers, the AV860 surround processor and the SR250 stereo AV receiver) and at some new products from NAD (such as the T758 V3 and the AM17 MDC card for the M17 AV Processor). Less known to us are devices from Datasat, AudioControl, Theta and Emotiva. Dirac Live is also available with the separate MiniDSP audio processors. Finally, you can also get started with Dirac yourself, by using a computer (Mac or Windows) as a music source. You then buy the software separately, which costs 389 euros for the stereo edition and 650 euros for the multichannel edition.
All implementations of which we are aware require that you bring out a laptop and a USB measuring microphone for the measurement. A microphone does not have to cost a large amount. There is the meritorious UMIK-1 of around 100 euros. You therefore perform the measurement on a computer, after which you are given the opportunity to adjust the frequency curve. Then the audio data is sent to a Dirac server, where the actual filters are calculated. A few seconds later you will receive those filters, which you then upload via the software over the network to the AV receiver. This method is very different from most AV receivers, but is, for example, comparable to what you have to do if you want to make filters with the free REW that you apply in Roon.
Our experiences
We already knew Dirac from a previous test of the separate Dirac Live software, where we used a Mac mini as source, connected to a USB DAC. That test has been in the past for a while and was not as thorough as the software deserved. So it was a good thing that, with the cooperation of Arcam and Transtel, we were able to work with an AVR390 and AVR550 for a number of weeks, in combination with different speakers, including the new Monitor Audio Silver series. Both the Arcam AVR550 and the Monitor Audio Silver series will soon be featured in their own tests on HiFi.nl and Home Cinema Magazine.
Also interesting was the session at Alpha High End in Brasschaat, which took place in a listening room of the store. What made it interesting is that this space – which in itself was treated very well and certainly didn’t sound bad – could still be optimized via Dirac. The improvement was clearly audible, both when we optimized only with a stereo setup and afterwards with an Atmos setup with four height channels. With the latter, for example, it was striking how the famous Dolby rainstorm demo suddenly became much more realistic. Instead of a roar of rain, you could actually hear water droplets clatter after optimization. The improved impulse response was mainly responsible for this.
As you would expect, the measurement procedure at Dirac technology is very extensive. You have to take seven measurements and that in a fairly accurate way. You must also properly adjust the volume levels of each speaker in advance. No problem with a stereo setup with the same speakers, but with a surround setup with nine speakers and a subwoofer, a little more work. But necessary, because different speaker models are often used in surround setups and sometimes the sensitivity of speakers differs greatly.
After the measurement, Dirac technology serves an optimization curve that you can adjust manually. The Swedes are inspired by studies that attempted to determine the ideal frequency curve by questioning. The result is a curve that peaks at low frequencies and then descends. If you follow the curve that Dirac recommends, we think you will end up with a boring reproduction where the voicing of the speaker disappears.
Arcam is of the same opinion and that is why Andy Moore, together with his colleague Allan Davidson, advises to adjust the proposed curve somewhat in the higher frequencies. The great thing is that you can create filters several times after one measurement, in order to ultimately arrive at the correct result. This requires practice, because the Arcam sessions clearly showed that adjustments must be made with a very gentle hand. A frequency peak or drop of 0.5 to 1 dB made Lou Reed’s ‘Walk on the wild side’ (the reference track during the sessions) sound completely different.
A downside is that the current Arcam products are not equipped with multiple filters. When you make a curve adjustment, you have to process it and then send it to the receiver. You can switch it on and off on the receiver, but you cannot switch between, for example, three filters that you want to compare. Hopefully that is something that Dirac and partner manufacturers will make possible in the future.
Do not expect miracles
Does all this mean that Dirac technology can really solve any problem? In theory, says Moore, but in practice it’s not a good idea. Adjusting a peak or valley with more than 5 dB is not recommended, he says. For certain problems you will therefore still have to tinker with the room itself, for example with diffusers or damping. And you can’t fix bad hardware. “All calibration systems work best when they have to compensate just a little bit. You have to ensure that a system performs as well as possible before you use a system like Dirac. ” The checklist presented by Arcam during its advanced Dirac training always recommends that installers first get the speaker positioning right, lay cables properly and position speakers stably. First the basics, then Dirac.
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