Bringing the 2L Mastering Room to VIRTUOSO v2.3

We are delighted to announce that APL VIRTUOSO and VIRTUOSO Lite now include a new 2L Mastering Room preset, created in collaboration with Morten Lindberg.

This is a particularly meaningful release for us. It is not simply the addition of another room preset. It is the result of our long-standing exchange of ideas, philosophy, and techniques with Morten, all centred on the pursuit of the highest possible standards in immersive audio recording, reproduction, and binaural delivery.

Morten Lindberg and the 2L Mastering Room

Morten Lindberg, founder of 2L, is one of the world’s most respected immersive recording engineers, with 50 Grammy nominations and two wins across the craft categories of Best Engineered Album, Best Surround Sound Album, Best Immersive Audio Album and Producer of the Year. His productions are widely admired for their pristine resolution and spacious, enveloping rendering of acoustic space, achieved through his microphone arrays 2L Cube and 2L PRISM.

For final delivery, precise monitoring is essential, and the 2L Mastering Room is one of the finest immersive audio reproduction environments in the world. Designed specifically for immersive work, it offers exceptionally accurate acoustic performance and conforms to all criteria specified in ITU-R BS.1116-3 recommendations.

The room was built to avoid discriminating directionality and to provide a spacious, enveloping listening experience across the full audible range. With carefully controlled reflections, diffusion, absorption, low-frequency treatment, and a Genelec ONE + W 9.1.6 monitoring system, it delivers a listening experience that is both rich and highly detailed.

Emulating the room in VIRTUOSO

The new 2L Mastering Room preset in VIRTUOSO v2.3 has been developed to reproduce the essential acoustic character of this remarkable space with a very high degree of accuracy. Across all key acoustic parameters, including reverberation time (RT60), room response, early reflection level, clarity (C80), interaural cross-corrlelation coefficient (IACC), and direct-to-reverberant ratio, the emulation achieved measured errors within just-noticeable-difference thresholds, which means there is minimal audible difference between the real and virtual rooms. Following extensive scientific validation and tuning by Prof Hyunkook Lee of the APL, the perceived quality of the room emulation was also endorsed by Morten himself.

The result is a preset that serves two purposes. For engineers and producers, it provides a highly reliable virtual environment for monitoring and quality control. For music listeners, it offers the opportunity to experience immersive playback in one of the world’s most acoustically precise mastering rooms, wherever they are.

Why room acoustics matter in binaural listening

In binaural rendering, room acoustics are not an optional extra. Acoustic cues such as early reflections and reverberation play a vital role in making sound feel externalised, supporting accurate localisation, and creating a convincing sense of presence. Without these cues, binaural listening can resemble listening in an anechoic chamber, which most people perceive as unnatural.

At the same time, not all room acoustics are beneficial. Excessive reflections, uncontrolled reverberation, and poorly balanced room responses can introduce comb filtering and undesirable colouration. This is exactly why standards for critical listening rooms, such as ITU-R BS.1116-3 and IEC 268-13, exist.

Drawing on more than 20 years of our research into the psychoacoustics of 3D audio and room acoustics, VIRTUOSO uses ASPEN‘s perceptually optimised virtual acoustic simulation to reproduce the benefits of a real listening room while avoiding unpleasant room-related artefacts. The goal is not simply to add “reverb”, but to recreate a trustworthy acoustic reference for monitoring, quality control, and immersive listening.

A shared workflow for remote QC

This collaboration also reflects a practical workflow we have already been developing together. Through the VIRTUOSO partnership programme, Morten has been using VIRTUOSO and VIRTUOSO Lite to support remote quality control with his clients and collaborators.

As Morten puts it:

In the process of immersive music production, we actively invite composers, conductors, and musicians to participate as directly as possible. Between attended sessions, we provide our project partners with the APL Virtuoso software, which now emulates our 2L mastering studio. The ADM file format allows for remote evaluation of edits, mixes, and masterings with reliable sonic qualities. APL Virtuoso overcomes traditional limitations in binaural rendering, offering a glimpse into the potential of future immersive virtualization for headphone listening.

This is exactly the kind of application we believe will become increasingly important in immersive production: enabling reliable remote evaluation without giving up the acoustic qualities of a trusted reference room.

ADM playback and the APL-2L offer

The collaboration also highlights the value of ADM as a master format for immersive audio production and delivery. By combining object-based metadata with lossless audio, ADM preserves the full fidelity and flexibility of a production for rendering, exchange, and delivery. Both the VIRTUOSO and VIRTUOSO Lite standalone apps include ADM playback, allowing users to experience immersive releases in true master-quality form. Morten has already been using this capability to support remote QC with his clients.

To help more people experience immersive recordings at mastering quality, APL and 2L are currently offering a joint promotion:

• VIRTUOSO and VIRTUOSO Lite is available at up to 50% off until 31 May.

• APL customers will receive a voucher for 20% off 2L ADM files or any other products from the 2L Music Store.

• 2L customers will receive a voucher for an additional 10% off VIRTUOSO and VIRTUOSO Lite during this period, and 20% off the regular price thereafter.

A shared vision

For us, the inclusion of the 2L Mastering Room preset in VIRTUOSO v2.3 represents more than a product update. It reflects Morten’s and our shared belief that immersive audio should be delivered with both highest possible quality and perceptual realism, and that binaural headphone listening can go far beyond its traditional limitations when the room, the rendering, and the monitoring philosophy are all treated with the seriousness they deserve.

We are proud to bring this collaboration to VIRTUOSO users, and we hope it will help both professionals and listeners experience immersive audio in a new way.

Creating a truly realistic binaural listening experience takes more than just good HRTFs. To make headphone reproduction sound natural, convincing, and speaker-like, two other elements are just as important: room acoustics and head tracking.

Without them, even binaural rendering with accurate directional cues can still sound unnatural or unstable.

HRTFs Alone Are Not Enough

Head-related transfer functions (HRTFs) are essential for binaural reproduction because they provide the directional cues our ears use to localise sound. But HRTFs on their own do not guarantee realistic externalisation.

When binaural audio is based only on anechoic HRTFs, sounds tend to become internalised – perceived inside the head rather than out in space. This is like listening in an anechoic chamber, where there are no natural room cues and distance perception becomes limited, relying heavily on loudness alone.

Furthermore, when listening to anechoic or very dry binaural audio in a lively room, the brain has to reconcile the visual and acoustic cues of the physical space with the unnaturally dry sound presented over headphones. This mismatch can make externalisation more difficult and increase cognitive load.

That is why room acoustic simulation is so important.

Room Acoustics Help Sound Leave the Head

A realistic sense of externalisation depends heavily on the acoustic context around the sound source. Reflections and reverberation help the brain interpret where a sound is located and how far away it is.

APL VIRTUOSO’s perceptually optimised, natural room simulation helps provide this missing context, making binaural listening feel far more like listening to real loudspeakers in a real space. It supports stronger externalisation and a more believable sense of space, while preserving the tonal integrity of the original source, much like listening in a very well-treated studio through premium monitor speakers. VIRTUOSO’s high-quality binaural rendering has been validated in academic research and endorsed by many world-class sound engineers.

But even with a perfect room simulation, something important is still missing if the listener’s head remains perfectly still.

Real Hearing Is Dynamic, Not Static

In everyday listening, we rarely hear the world with our head completely fixed. Even very small head movements continuously update the binaural cues reaching our ears, including interaural time and level differences, and spectral changes.

These dynamic changes are a fundamental part of how we localise sound and judge auditory distance.

With static binaural listening, those updates are absent. As a result, some sounds, especially those positioned directly in front, such as a phantom centre or real centre channel, may still not feel immediately externalised, even when the room simulation is good.

Head Tracking Makes Binaural Audio Feel Real and Natural

Head tracking restores the natural dynamic behaviour of hearing. As the listener moves, the virtual sound field updates accordingly, just as it would with real loudspeakers. This makes externalisation stronger, localisation more accurate, and the entire listening experience more natural and convincing. When dynamic cues are missing, listeners may need to work harder cognitively to interpret the virtual sound scene. Head tracking helps relieve that effort by giving the auditory system the information it naturally expects.

Head tracking is especially important in headphone mixing because it stabilises the virtual sound stage and makes spatial positions feel more natural and speaker-like. In immersive work, this helps engineers judge localisation, depth, width, and front-back placement more accurately, leading to more reliable mix decisions and better translation to loudspeaker playback.

A Solution to Front/Back Confusion

One of the most persistent problems in binaural reproduction is front/back confusion – when a sound in front is misperceived as coming from behind, or vice versa. Head tracking plays a crucial role in reducing this problem.

A slight turn of the head causes opposite cue changes for front and rear sources, giving the brain the information it needs to distinguish between them. Research has shown that even with personalised HRTFs, front/back confusions can remain significant when head movement is restricted. Allowing even small head rotations can substantially reduce these errors and improve spatial realism.

APL VIRTUOSO + HeadTrek

APL HeadTrek is a lightweight, camera-based head tracking solution designed to work seamlessly with APL VIRTUOSO on macOS.

Free for both existing and new VIRTUOSO users, it uses standard webcams or built-in cameras to track head orientation in real time and transmit that data directly to VIRTUOSO. This enables more accurate binaural monitoring and a more immersive listening experience, without the need for specialised hardware.

The result is a practical and accessible way to bring binaural reproduction closer to the realism of real loudspeaker listening.

The Bottom Line

Realistic binaural audio is not just about reproducing the right directional cues. It is about recreating the way we naturally hear sound in space.

HRTFs provide the directional foundation, but on their own they are not enough. Room simulation provides the acoustic context that helps sounds externalise naturally, convey distance, and preserve a believable sense of space. Head tracking then brings the experience fully to life by restoring the dynamic cue changes that occur as we move our head in everyday listening.

Together, these elements make binaural listening more natural, immersive, and much closer to the experience of hearing real loudspeakers in a real room.

Our new study introduces a more efficient way to analyse and auralise room reflections in spatial audio!

We published a new paper in Applied Acoustics presenting a method that could improve how room acoustics are analysed, represented and reproduced in spatial audio systems. The study, titled “Spatial segmentation of impulse response for room reflection analysis and auralization,” was authored by Dr Alan Pawlak and Prof Hyunkook Lee. It was Alan’s PhD project supervised by Prof Lee and funded by Genelec Oy. 

The paper introduces a new technique called Spatial Segmentation of Impulse Response (SSIR). It was developed to address a longstanding challenge in parametric spatial audio reproduction: representing early reflections in a way that is both perceptually accurate and more manageable for analysis and creative control. Early reflections play a major role in how listeners perceive space, source width, timbre and realism, yet existing methods can make them difficult to isolate and manipulate effectively. 

SSIR works by detecting and segmenting early sound events within measured spatial room impulse responses (SRIRs), allowing individual events to be represented more compactly while remaining within the framework of the well-established Spatial Decomposition Method (SDM). According to the paper, this enables more efficient spatial representation and greater control of individual reflections without sacrificing perceptual performance.

To evaluate the method, the researchers carried out two perceptual experiments. The first tested overall fidelity by comparing SSIR with an optimized SDM variant, a reflection extraction method and a dummy head reference. The second focused on spatial and timbral fidelity, comparing SSIR against both the original SDM formulation and the optimized SDM variant. The results showed that SSIR delivered significant improvements in spatial and timbral fidelity over standard SDM, while showing no significant perceptual difference from the state-of-the-art optimized variant. It also outperformed an early reflection extraction approach.

Importantly, the study reports that SSIR achieved this while reducing the complexity of spatial data and preserving key perceptual qualities such as apparent source width and externalisation. This makes the method promising not only for room acoustic analysis and auralisation, but also for psychoacoustic research and future spatial audio tools where efficient yet perceptually robust room representation is needed.

Our new paper has been published in this month’s issue of the Journal of the Audio Engineering Society. This work from Miki Morinaga’s Masters by Research project, supervised by Prof Hyunkook Lee at APL, identifies salient perceptual attributes of 3D microphone arrays and shows that the off-centre listening positions in immersive audio playback can lead to greater variations in the perceived differences among the arrays. Tonal attributes such as clarity, fullness,and brightness were found to be particularly salient in off-centre positions.

This paper forms Part 2 of the 3D Microphone Array Comparison (3D-MARCo) research series. Part 1 focused on objective measurements of the arrays, which provide theoretical explanations for some of the findings reported in this paper. Since the 3D-MARCo open-access database of high-quality 3D mic array recordings was published in 2019, it has been downloaded 43,000 times, and has generated numerous academic and industrial impacts, helping engineers, educators, students and researchers learn how to capture 3D sounds, and more broadly, how to listen to and evaluate spatial audio. The journey is still continuing, inspiring our sister ECHO-Project as well as other spatial audio and AI research projects. Part 3 will come one day.

I’m excited to share that my paper, “A Unified Conceptual Model of Immersive Experience in Extended Reality” has been published in Computers in Human Behavior Reports (Q1, IF 4.9)! The initial manuscript of this paper has been available as a preprint on Psyarxiv for nearly 5 years, so I am especially glad to see it finally find a home. It’s published Open Access and can be accessed freely here.

This paper explicates various underlying concepts of immersive experience and proposes an overarching conceptual model that can serve as a foundation for systematically and consistently assessing immersive systems and experiences.

A persistent issue in this research field is the inconsistency in terminology: different researchers use different terms for the same concepts—or the same terms for different concepts. Immersion is often used by some researchers to describe the technological process, while others use it to refer to a psychological state. This lack of conceptual clarity makes it difficult to compare studies and build a coherent body of research around immersive experience in XR.

While there are existing definitions of immersion, they often focus solely on either the system’s sensory simulation capabilities or the user’s cognitive engagement. But both aspects are essential, and they influence each other. Immersive experience is a complex, multidimensional construct, and no single standardised questionnaire can fully capture it across different contexts. When designing studies or evaluating the immersive potential of systems or content, it is crucial to understand the dimensions of immersion, the related concepts, and their conceptual hierarchy.

In this model, I first propose using a clear terminology: Immersive Experience (IE) and Immersive System (IS), rather than just immersion. This helps avoid confusion.

The model considers three core dimensions of immersive experience, which encapsulate a wide range of immersion-related terms found in the literature. The typology of Presence is based on Biocca (1997)’s but with slightly revised definitions to cover AR/MR as well as VR.

• Physical Presence (PP)
• Social Presence & Self Presence (SP)
• Involvement (INV).

PP, SP and INV are enabled by three preconditions:

• Sensorimotor Engagement
• Task/Motor Engagement
• Narrative Engagement

These are influenced by the properties of IS and content:

• Plausibility
• Interactivity
• Interestingness

, while also being modulated by subjective factors:

• Internal Reference (due to prior experiences and cultural background)
• Skill/Knowledge
• Personal Preferences

Please read the paper to find out more about the model. I hope this unified model contributes to a clearer understanding about immersion and provides a useful framework for researchers and practitioners working in XR.

Train Journey, 1st mov. (2024) – Volker Berterlmann (Hauschka)
Orchestral layout: Circular
Mic array: 2L Prism – Morten Lindberg

Atmos 7.1.4 – Binaural

Kammersinfonie für 23 Soloinstumente (1916) – Franz Schreker
Orchestral layout: Traditional
Mic array: AIR Cage – Nick Wollage

Atmos 7.0.2 – Binaural

Decca Tree (L/C/R only) – Stereo

Orchestral Layouts

Circular layout

The orchestra is positioned around the microphone arrays.

Traditional layout

The orchestra was in the front facing the conductor, with the arrays positioned right behind the conductor, facing the orchestra.

Microphone arrays are particularly important in channel-based audio, especially for capturing the acoustics of a space as well as sound sources. When properly designed, they allow for accurate spatial and tonal reproduction of sound field. The configuration of an array can be adjusted through various factors, including the type of microphone, polar pattern, spacing and angles between capsules, and finally, the placement of both the array and the musicians.

The ECHO Project invited seven expert recording engineers to explore their approaches to immersive orchestral recording. Seven microphone arrays, each tailored to a specific recording scenario—classical, film score, or game soundtrack—were used to capture the performance of the London Contemporary Orchestra in both traditional and circular layouts at AIR Lyndhurst Hall. Below, each focus group recording engineer presents their rationale behind their chosen array. Click here to find out about the orchestral setups and musical pieces recorded.