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!

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.

Dirac Dr Lars-Johan Brännmark

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.

Dirac Live

Better Sound for ALL Listeners

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
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.

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

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.

Co-optimization = Better Bass

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.

Dirac graph 1

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

Dirac graph 2

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.

Dirac graph 3

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?

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.

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.

dlaloum posts on September 11, 2022 01:43

buckchester, post: 1570971, member: 78944
This article reads like an advertisement. I am sceptical of the claim to make an EQ profile that will improve every seat. Also, shouldn’t these things simply focus on the frequencies that are controlled by the room (Below the room transition frequency)?

And how is one room correction tech better than another? Audyssey, ARC, Dirac, etc. As long as they have enough filters to smooth out the frequency response for the main seat below the room transition frequency, what would be the difference from one to another?

It’s not EQ – it’s more like noise cancelling – yeah the overall package includes EQ, and time alignment, impulse optimisation…

But really what they are talking about here is more like what is achieved in Noise Cancelling headphones – Trinnov already do some very similar mathematical magic with their setup…. This brings that type of tech into the mainstream (ish) price bracket.

VonMagnum posts on September 10, 2022 23:36

I’m not sure how this is supposed to work in an Atmos type system. I’ve got 17 speakers and three rows of seats in my home theater and one of the biggest problems is attenuation over distance of the mains to the back row and louder levels of rear speakers near that row to get even levels in the front row where the MLP is located.

I keep three “Smart Settings” for this. I’ve got optimized levels for the front row, the second row and a compromise between the two. The only way to further improve things was to create mixed arrays of the rears in ss#2 so they could help with levels closer to the front without having to play them as loud.

So how could you get levels even in the back and front except to use speakers not intended for those sounds (e.g. Side surrounds) to play content meant for the
L/C/R mains with delay to reinforce the sound over distance like you would for a live concert? The problem, of course is your system is no longer fully discrete and I’m afraid most Atmos fans wouldn’t like that one tiny bit given some of the derision I’ve gotten over using arrays (as if they’re evil; they make the experience better IMO for more seats, but this “discrete” obsession doesn’t jibe with expectations.

Of course, maybe they’re not addressing that at all with this system, just nearby frequency response, but that’s relatively easy to deal with using conventional room treatments above Schroeder….

TLS Guy posts on September 01, 2022 15:21

flak3, post: 1571279, member: 98452
An interesting and unique aspect of this technology is the fact it takes advantage of the capabilities of large floorstanders at low frequencies which is not the case when bass management is used for subwoofers.
The technology can make use of the energy from the main speakers in low frequencies as well when there is an overlap, rather than only depend on the subwoofers.
Also, at certain frequencies there will be more sources and this will offer more degrees of freedom to the algorithm so even a Stereo system with two subs will have four different sources of low frequencies.

That is a plus, and the way my system is designed. I have maintained here that crossing to subs with generic receiver/pre/pro crossovers is actually bad engineering.

flak3 posts on September 01, 2022 11:36

An interesting and unique aspect of this technology is the fact it takes advantage of the capabilities of large floorstanders at low frequencies which is not the case when bass management is used for subwoofers.
The technology can make use of the energy from the main speakers in low frequencies as well when there is an overlap, rather than only depend on the subwoofers.
Also, at certain frequencies there will be more sources and this will offer more degrees of freedom to the algorithm so even a Stereo system with two subs will have four different sources of low frequencies.

CreoleDC posts on September 01, 2022 00:49

mtrycrafts, post: 1571232, member: 5380
What? Swiss chocolate is inferior?

We don’t talk about “inferior”. here’s a link I’m gonna post up see which one Dr. Toole would choose over the other. Swiss? or German chocolate.