Calibration: The Final Step in Immersive Audio Design
- CALIBRATION, DIRAC LIVE ART
You’ve designed and integrated an immersive audio system. You’ve understood the customer’s needs; specified the right speakers, subwoofers, and AV technology to fill the space with sound; and optimized acoustics based on your reading of the room. But you’re not finished.
Yes, you’ve completed 90 percent of the work, but the last 10 percent will determine whether your efforts created the intended listening experience. It’s time to perform the necessary calibration — a critical step that shapes the acoustical response of the audio system.
To help, every StormAudio Immersive Sound Processor (ISP) comes with powerful calibration tools to streamline and improve this all-important phase. But first, let’s step back and explore how you got here.
Calibration as the Last Step in Sound Optimization
In the process of designing the audio system, it has been important to follow industry norms, including the CEDIA/CTA-RP22: Immersive Audio Design Recommended Practice. Having consulted with the end user, the system design should meet a set of sound reproduction goals, including:
- Clear dialog and articulation
- Precise sound localization
- Smooth sound movements
- Sound field immersion and envelopment
- Even tonal balance
- Full dynamics
Ultimately, every seat in the listening area should be a good seat, with full audience coverage and appropriate bass impact everywhere.
Of course, no matter what speakers and AV technology you specify, it’s critical to account for the room itself. Once you turn on an immersive audio system, most of what people hear is the effect of the room — its dimensions, walls, furniture, and windows. Reflected sound wreaks havoc on a listening experience through room mode excitation, resonances, reverberation, frequency interference, and recombination. Sound becomes unnatural, through boomy, uneven bass, coloration, and a lack of clarity across the soundstage.
There are several necessary steps to overcoming the effects of the room. Many integrators start with a detailed room analysis, to optimize the seating and subwoofer locations. They may employ multiple subwoofers to optimize seat-to-seat sound variation. It is likely also necessary to apply acoustical treatments — absorption and diffusion, bass traps, etc.
The final, necessary step is to perform the required calibration, which effectively “removes” the room from the immersive sound experience. Through calibration, the integrator creates filters in the AV processor that adjust the system’s magnitude and phase responses, thereby aligning and shaping the speakers’ overall acoustical response against a target frequency curve.
Why Calibration is Important
Every listening space benefits from calibration, whether it has a two-channel stereo system or a multichannel, immersive system. The best way to approach calibration is to wait until the room and audio system are as finished as possible. The audio system is under control of the integrator, but if the homeowner plans to install shelving, purchase new furniture, or hang framed movie posters, wait to proceed. Calibration will be meaningless unless the room is exactly how it will be experienced.
Rooms vary in size, shape, furnishings, building materials, and related acoustic properties, which impact the way sound waves interact and propagate. Through calibration techniques, such as room correction and bass management, problematic acoustic characteristics — echoes, reverberation, and standing waves — can be mitigated, leading to a more consistent, immersive listening experience.
The goal of calibration is to achieve accurate and balanced sound reproduction. By calibrating speaker levels and EQ settings, integrators ensure that sound is distributed evenly across the frequency spectrum, minimizing peaks and dips in volume and frequency response. This results in a more natural and lifelike audio experience.
Traditional calibration, using sound level meters, measurement microphones, equalization, and other tools, focuses mainly on time alignment among speakers and shaping the sound they produce. What standard calibration tools cannot do, however, is correct properly for major room resonances and decay time in the low frequencies. In most cases, this must be accomplished using bulky, passive acoustic treatments, like bass traps, diffusers, and acoustic panels. Today, however, integrators can perform a more complete calibration — including adjustments for room acoustics — through software.
The Power of Calibration Tools
StormAudio Immersive Sound Processors possess a powerful calibration toolset, including the most advanced implementation of Dirac Live. Like most calibration tools, Dirac Live uses microphones placed throughout the listening space to capture its acoustic properties and collect data about frequency response, phase, impulse response, etc.
Dirac Live is run on the integrator’s laptop computer to analyze the room’s acoustics and manipulate settings to mitigate room resonances; reduce bass lingering by controlling decay time; and meet the desired target curve.
The software then generates filters that are uploaded to the AV processor. These filters adjust the audio signal in real-time as it passes through the system, correcting for the room’s acoustic characteristics and optimizing the sound output.
Specifically, Dirac Live’s Active Room Treatment module (also known as ART) does something unique in its calibration. It uses all the available speakers — including subwoofers — to reinforce one another. With ART, speakers emit sound waves that interfere with and cancel out unwanted reflections and resonances. They are controlled by algorithms created after analyzing the room’s acoustics and applied in real time. In some ways, the technology behind ART is like active noise cancellation in headphones, though, it compensates for existing room issues instead of real-time noise variations.
In terms of calibration, Dirac Live offers several key benefits. Used properly, the solution:
- Calibrates speakers as a unified system, using the speakers to control the room — not the other way around.
- Actively cancels out lingering excess bass to reduce room decay time and eliminate bass smearing.
- Optimizes sound performance across a wider area for a larger, more uniform “sweet spot.”
- Reduces the need for bulky and expensive in-room, low-frequency acoustical treatment.
After a Dirac Live-calibrated system is operational, it is important to listen to various audio content and evaluate the result. Depending on the owners’ preferences, integrators may need to optimize Dirac Live settings for different types of content.
For a complete introduction to Dirac Live Active Room Treatment, please view this webinar.
How to Successfully Use Dirac Live Active Room Treatment
When using Dirac Live Active Room Treatment for calibration, integrators can focus on frequencies above 150Hz with passive treatment, while the tool will manage the rest actively. It is still recommended to still use passive room treatments below 150Hz; ART reduces the need for such treatments but does not negate it. Ultimately, ART improves impulse response and decay time under 150Hz and significantly decreases the need for bulky passive treatments.
Crucially, all speakers in an audio system can be used for ART calibration. When it comes to low frequencies, the tool can achieve good results without subwoofers, particularly if the system’s other speakers span a wide band. But subwoofers should be considered in ART calibration for the best LFE reproduction. Ultimately, the number of support speakers depends on AV processing power.
When it comes to using Dirac Live Active Room Treatment for calibration, keep a few things in mind:
- Make sure to use the latest version of Dirac Live Active Room Treatment.
- Make sure your StormAudio ISP has firmware 4.5r0 or later.
- Know your speakers well and what they’re capable of, including rated bandwidth, because you’ll need to enter them precisely in the ART tool. Speaker data sheets help. Always give your speakers a little bit of breathing room between their published low frequency point and the low frequency of their support in the ART tool.
- You can use existing Dirac Live projects with ART, as long as they include enough room measurements—at least nine per speaker.
- If you don’t have a project to start from, the process is largely the same as with other Dirac tools: microphone selection and calibration, level adjustment, arrangement selection, measurement, and filter design.
When it comes to designing filters, adjust the target curve to suit the homeowners’ expected sound coloration. Alternatively, you can define them using Dirac’s auto-target curve or download StormAudio’s recommended target curves. Note: Whatever route you take, a flat curve is not recommended.
As expected, with a higher degree of complexity and signal processing power, a higher knowledge and understanding of system’s filter design is required. However, instead of creating a new myriad of complex acoustical problems, ART allows the entire system to function as a whole cohesive unit like never before. Thus using the room measurement data to actively manipulate and improve the room’s acoustical coherence in a manner that has to be experienced to be fully understood.
For more detailed guidance on calibration using Dirac Live Active Room Treatment, watch this StormAudio webinar. For consideration of StormAudio’s dedicated engineering team curating Active Room Treatment for your system please consult your local integrator.
Happy Calibration
Calibration is key to ensuring immersive audio systems deliver high-quality sound experiences. By fine-tuning various audio parameters and addressing acoustic challenges, calibration enhances the accuracy, clarity, and realism of sound reproduction, allowing listeners to fully engage with their content.
Calibration with Dirac Live Active Room Treatment, available on StormAudio Immersive Sound Processors, effectively removes room effect and replaces bulky room treatments. It reduces lingering bass and controls the decay time; creates a larger, more uniform sweet spot; and fills the room with more even, defined, tight bass.
You specified the best speakers for the space you’re working in. You don’t want the room to ruin this investment. Get the most out of each speaker and subwoofer through active room calibration.
