Will Dirac’s New Active Room Treatment Minimize Need for Passive Treatments?

Imagine a "spatial" room correction to let all speakers work together to correct each other to overcome acoustical problems and get good sound at every seat. Dirac's on the cusp of making this a reality for you!

Over the past two decades, room-correction has become such an important part of the home theater industry that some consumers will only consider buying a certain AV processor or receiver if it has a specific room-correction technology on board. For example, the high-end AV processors from Trinnov fetch such steep prices largely because that company’s proprietary software — including room correction — is so powerful and flexible. For my money, the only DSP-based room-correction solution that competes on even ground with Trinnov is Dirac Live, which has slowly but steadily become one of the most sought-after features in mainstream audio components. Dirac Live is highly effective at compensating for certain room acoustics problems, improving overall performance in either a stereo or surround-sound system. It can be found in a wide variety of products, from affordable NAD integrated amps and Onkyo AV receivers, all the way up to state-of-the-art AV processors from the likes of Storm Audio and JBL Synthesis. Despite this success, the scientists at Dirac Research believe that the next generation of digital loudspeaker and room correction will go far beyond what is possible today, and the future may be closer than we realize.

Dr. Lars-Johan Brännmark, the Research Fellow and Chief Scientist at Dirac, recently wrote an article in audioXpress magazine outlining an entirely new approach to room correction that promises to revolutionize the industry by going beyond the frequency domain and time domain optimization employed in today’s solutions. Designed specifically for immersive audio systems (such as a Dolby Atmos home theater), Dirac’s new “spatial” room-correction takes advantage of the additional speakers required for immersive audio. For existing DSP room-correction systems, the complexity of these multichannel setups presents a challenge since each channel receives its own filter. After each loudspeaker is measured with a microphone, the room-correction system generates a filter to correct the speaker/room response for that channel. The process is repeated for every channel, and the time and frequency properties of each are optimized independently of the other channels. Dr. Brännmark suggests that this approach, as effective as it can be, simply isn’t sufficient when multiple people are listening from multiple locations within a dynamic space. Instead, Dirac’s proposed “spatial” room correction solution would use all speakers working together to optimize the reproduction of each input channel.

Better Sound for ALL Listeners

Today’s best room-correction systems, such as Dirac Live, can correct a signal in both the time and frequency domains, but the “spatial response” is left unchanged. What exactly is the spatial response? Dirac defines it as “the way the sound propagates and interacts with objects and room boundaries (and) the way sound pressure at one position relates to pressure at other positions.” For an immersive home theater, room correction must be “spatially robust,” according to Dr. Brännmark. That means the system needs to be able to improve audio performance throughout a spatial distribution of listener positions, not just in one sweet spot. Some rooms have such a complex room response that a small change in listener position results in a very large change in frequency response. In such a room, standard room-correction filters are more limited in what they can achieve. Simply put, traditional room-correction methods (with one filter applied individually to a single channel) just aren't able to reshape a three-dimensional sound field in space. The solution, according to Dr. Brännmark, is something called loudspeaker co-optimization, in which all of the speakers in a given system work together to reproduce each input channel in an optimal way. In such a system, multiple speakers could cooperate, with room-correction filters operating simultaneously on several speakers throughout the space. This concept is similar to what Dirac has employed in its Dirac Live Bass Control solution for multiple subwoofers, which reportedly “ensures that low frequencies add up so that not only the average is controlled, but most importantly, seat-to-seat variation is minimized as we can now achieve a level of control in multiple locations at once.” Multiple subwoofers are equalized and phase-shifted with regard to their in-room sum response, so that variations in seat-to-seat frequency response are limited in the common bass channel. What if a similar approach could be used, not just with one bass channel, but with all input channels across a much wider range of frequencies? That’s the goal of spatial room correction. Dirac believes that such an approach could “stretch a sound system spatially,” and help it reach its full potential.

DIRAC Spatial Room Correction - Revolutionize Audio Calibration? 

According to Dr. Brännmark, there has been some previous research into methods for achieving sound field control. The DSP and acoustics research communities have come up with various theories about the subject over the years, but most of that research has not resulted in products for the consumer audio market, other than a few beam-steering and binaural rendering applications used in devices like soundbars, TVs, and laptops. These methods rely on multichannel filtering (a.k.a. MIMO, or multiple input multiple output) combined with the physical principles of sound field superposition. What has prevented these technologies from finding their way into immersive home theater products? Dr. Brännmark suggests that it comes down to system complexity and sensitivity. If you want to combine sound from separate channels to achieve the desired spatial effect, the sounds produced by the various speakers and room reflections must add up in the right ways and at exactly the right times at multiple points in space. This level of precision places a high demand on system reliability and robustness, right down to equipment manufacturing tolerances and even the stability of electromechanical components over time. Despite these challenges, Dr. Brännmark claims that Dirac’s proposed system of loudspeaker co-optimization can achieve the desired effects for true spatial room correction. Via these techniques, a sound wave can be controlled in time, frequency, and space. This means that a user can control how a sound wave interacts with room boundaries — not just how it propagates from the loudspeaker to the listener. This control is what will allow all speakers in a complex multichannel system to work together to reproduce each input channel in an optimized way.

“Support” Speakers and “Super” Speakers

Typically, having more speakers means more challenges when it comes to room correction. But in Dirac’s spatial room-correction system, having a large number of speakers becomes an advantage. Loudspeaker co-optimization means that each speaker in the system will simultaneously play two roles. First, each speaker acts as a primary speaker, reproducing a specific signal for that channel, likely in need of some correction from the room-correction system. Second, each speaker also acts as a “support” speaker, used to correct other speakers in the room. Every speaker in the system is helped by the other speakers in order to achieve the target response. The goal is to get the optimal impulse response from each speaker, using other speakers as “support” speakers, in order to create a virtual “super” speaker. Instead of one speaker being used to reproduce each input channel, all speakers are used to reproduce each input channel. In the context of an immersive home theater system, this approach would allow for reflections to be effectively canceled and for room resonances to be controlled in ways that have never before been possible. For example, there might be no way to manipulate the signal sent to a source speaker so that its reflected sound — sound coming from the speaker and then bouncing off of a far wall or other reflecting surface — is controlled. But by enlisting the help of speakers located nearer to that reflecting surface, it would be possible to cancel reflections coming from that direction. And the use case for loudspeaker co-optimization isn’t limited to multi-channel audio sources; even a stereo recording can benefit. In a normal two-channel system, each input channel is played back by one of the two speakers, each working independently. The only way to address room modes is to add or remove power at certain frequencies. Even if the speakers being used can handle the increased power (this is not always the case), the sweet spot for the corrected response will be very small. If played back on a larger system with multichannel control, a stereo recording could benefit from the use of additional speakers to add or remove power in various positions, with different timing, all at the same time. The result, according to Dirac, would be a much larger sweet spot with more even bass reproduction and better timing.

Loudspeaker Co-optimization = Better Bass

As I mentioned earlier, the Dirac Live Bass Control solution for multiple subwoofers already demonstrates some of the benefits of co-optimization, but it deals with just one input channel. Dirac’s proposed MIMO control paradigm performs bass management differently, using true loudspeaker co-optimization. Subwoofers (and/or bass-capable full-range speakers) can be used to extend the frequency range of other speakers in the system with less bass capability, but  — and here’s the big advancement over previous systems — the bass content of separate input channels is not re-routed to a single bass channel. The bass content of each channel remains intact and is fed to separate speakers, which themselves have been corrected and bass-extended. Dirac says that immersive, multichannel content such as Dolby Atmos will enjoy “significantly improved correction with control in time, frequency, and space, including a higher degree of control over speaker and room response.” The overall sound should be tighter, with more extended low bass and reduced spatial variations in the room. But the benefits of co-optimization don’t stop with better bass. Consider this unusual advantage: loudspeaker co-optimization and spatial room correction are such powerful tools that users could actually “shape” the immersive sound field that they want. Just as shaping the frequency response of a system to match a certain target curve allows a user to “shape” the sound to taste with respect to frequency, it would be possible to shape the sound with respect to the spatial properties of sound. For example, users with a small or even cramped home theater could copy the spatial response of a larger, more comfortable theater room. If your retro living room is still sporting shag carpet, over-sized beanbag chairs, and velvet curtains, you might be suffering from dry, over-damped bass. Using loudspeaker co-optimization and spatial room correction, you could reshape the sound of your room without redesigning your pad.

The measured responses of an uncorrected system, in 64 microphone positions (grey lines) and their average (black line).

The measured response of a system using room correction based on single-channel technology. The average (black) is improved but spatial variations (grey) over different measurement positions remain.

The measured response of a system using loudspeaker co-optimization for room correction, reflecting a flattening out, a reduction in spatial variations, and cancellation of room resonances.

Room Correction Redefined?

It’s my understanding that Dirac’s spatial room correction technology is still in development, but Dr. Brännmark seems convinced that it represents the future, not only for Dirac, but for room correction in general. I’ll be curious to see what kind of processing power will be required to make it work. The first time I ever heard Dirac Live in action, it was running on a laptop (as a rather costly and fiddly add-on to the Amarra high-res music playback software) because at that time, purpose-built audio components simply didn’t have the necessary horsepower onboard. As we’ve seen from products like the $549 NAD MDC2 BluOS-D module (an optional add-on for the brand’s C 399 and C 389 integrated amps), Dirac Live can now run on small and relatively inexpensive hardware — a development that has surely contributed to the widespread adoption of the tech. Perhaps Dirac’s spatial room correction solution will eventually replace Dirac Live as the go-to solution for gear at all price points, or maybe it will only work on super-high-end products, like the Storm Audio AV processor in the Audioholics Smart Home. We’ll just have to wait and see.

Does an AV device’s onboard room correction software influence your purchasing decisions? Would you be more likely to buy a certain processor or receiver if it had Dirac Live, or a different solution that you prefer? Share your thoughts in the related forum thread below.