AES Europe 2025

Immersive audio has become a significant trend in music recording, reproduction, and the audio and entertainment industries. This workshop will explore microphone techniques for immersive sound recording from theoretical, aesthetic, and musical perspectives.

Capturing a music performance and its acoustic features in a specific reverberant field, such as a concert hall, requires specialized microphone techniques for immersive sound. Various microphone techniques have already been proposed for immersive music recording. Achieving a natural timbre, appropriate musical balance, wide frequency range, low distortion, and high signal-to-noise ratio are essential in music recordings for capturing the music performance, including immersive sound recording. The acoustic features of the musical performances can be naturally reproduced by appropriately capturing direct and indirect sounds in the sound field.

The first topic of this workshop will cluster and review microphone techniques based on their fundamental roles. The panelists will also introduce their immersive sound music recording concept, demonstrate their microphone techniques, and provide sound demos.

Immersive audio can expand the adequate listening area if the microphone technique is designed with this goal. This is crucial for popularizing immersive sound reproduction among music lovers. Therefore, the second topic of this workshop will discuss microphone techniques from the perspective of the listening area during reproduction. The panelist will explain his hypothesis that lower correlation values in the vertical direction contribute to the expansion of the listening area.

In immersive sound recording, various microphone techniques have been proposed to reproduce the top layer of the multichannel discrete loudspeaker layout. It is recommended to use directional microphones and position the top and middle layer microphones simultaneously to avoid phase differences that can degrade timbre. However, some reports suggest that separating the top and middle layers can enhance the perception of vertical spaciousness. Experiments conducted by the panelists also suggest that separating these layers and lowering the correlation between them can widen the listening area without altering the central listening position's impression. Comparing microphone types and installation positions in the upper layer is challenging in actual recording situations. Therefore, the panelists will compare listening impressions under various conditions and allow participants to experience these differences using virtual recording techniques (V2MA), which will be discussed as the third topic of this workshop.

Several papers have reviewed microphone techniques, but most have relied on subjective evaluation. The third topic of this workshop will attempt to evaluate microphone techniques from a physical viewpoint. The panel will introduce the Virtual Microphone Array technique (V2MA) to determine how each microphone captures a room's reflection sounds and identify the acoustical features of several microphone arrays used for immersive sound recording. V2MA generates Spatial Room Impulse Responses (SRIR) using a virtual microphone placed in a virtual room with spatial properties of dominant reflections previously sampled in an actual room.

Lectures and demos help us understand the acoustical features and intentions behind microphone techniques, but they are insufficient to grasp their spatial characteristics, especially for immersive sound recording. The panelists will provide 7.0.4ch demos to showcase the spatial features of microphone techniques using V2MA. V2MA generates the acoustic response of a microphone placed virtually in a room, calculated from spatial information of virtual sound sources, such as dominant reflections detected from sound intensities measured in the target room. This workshop will illustrate the spatial characteristics of microphone arrays, allowing us to discuss the types of reflections captured by microphones and discover the differences in spatial features between microphone techniques.

Following each panelist's presentation, a panel discussion will delve into microphone techniques from theoretical, aesthetic, and musical viewpoints. This workshop aims to review issues with microphone techniques for immersive sound and discuss potential solutions to achieve natural spatial reproduction of musical performances for home entertainment.

*Introduction
With the growing market of immersive audio, both new and exciting production possibilities are emerging, alongside the resurfacing of existing surround sound production techniques. As audio production continues to evolve, understanding the impact of temporal properties on spatial perception becomes increasingly critical. One of the most effective ways to create a sense of space and depth, as well as to enhance listener envelopment, is through precise manipulation of temporal characteristics of sound.

*Temporal Adjustments in Audio Production
In stereophonic recording techniques, spatialization is often achieved by carefully controlling both each microphone’s distance from the sound source and the distance between microphones, in conjunction with leveraging variations in microphone sensitivity through polar patterns and directional rejection.
These distance-based variations introduce time delays, which are fundamental to spatial localization and depth perception. Similarly, in post-production workflows, delaying and applying differentiated effects to signals serve as powerful tools for enhancing immersion and spatiality. The controlled use of delay, reflections, and micro-temporal variations plays a significant role in shaping perceived auditory space. These techniques are widely used in both as mixing approaches with music and also sound design where artificially introducing delays helps simulate the propagation of sound in physical spaces, creating a more authentic and immersive auditory experience.

*Psychoacoustic Phenomena and Spatial Perception
Closely delayed or slightly altered signals give rise to psychoacoustic effects that influence spatial perception rather than purely temporal perception.
For instance, the number, spectral characteristics, and temporal distribution of reflections can lead a listener to perceive an auditory environment akin to a concert hall, even in the absence of an actual reverberant space.
The well-known Haas effect (precedence effect) provides insights into how human perception prioritizes the first-arriving sound over subsequent delayed versions, influencing localization and clarity. Additionally, the concepts of Temporal Integration Window (auditory signal fusion) describe how multiple signals originating from the same source are perceptually fused into a single event, affecting spatial coherence and envelopment.

*Workshop and Study Overview
This workshop presents and exemplifies findings from an ongoing semester-long study, which is currently being prepared as a submission to the Journal of the Audio Engineering Society. The study investigates whether sensation, timbral perception, and temporal integration windows are influenced when the delayed signal's spatial position is altered. By showcasing how spatial modifications of delayed signals affect auditory perception, the workshop aims to contribute insights to the field of immersive audio production.

*Conclusion
This research underscores the importance of temporal manipulation in immersive audio, bridging psychoacoustics with production techniques. By examining spatial perception through the lens of delay-based processing, the study offers new perspectives on designing more effective immersive sound experiences. The workshop will provide participants with theoretical insights and practical examples, encouraging further exploration of the intersection between temporal properties and spatial audio design.