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PROCEEDINGS of the
24th International Congress on Acoustics
October 24 to 28, 2022, in Gyeongju, Korea
Extended abstract
Online acoustic recording education using MARRS
Hyunkook LEE
1
; Nikita GODDARD
1 Applied Psychoacoustics Lab (APL), University of Huddersfield, HD1 3DH, Huddersfield, United Kingdom
ABSTRACT
This extended abstract first discusses the importance of teaching and learning spatial audio psychoacoustic
principles in acoustic sound recording education. Then it introduces an interactive Web Audio application
named MARRS for Web, which has been used for the online teaching of a spatial recording module at the
University of Huddersfield during the pandemic period. MARRS (Microphone Array Recording and
Reproduction Simulator) provides an interactive visualization of the perceived image position of sound
source as the user changes the position and configuration of microphones. The Web version of MARRS also
provides a stereo and binaural playback of a virtual quartet with the user’s chosen sound files and room
impulse responses. The tool has been found highly useful not only for teachers to explain theoretical
principles of stereophonic imaging in stereo microphone array recording, but also for students to have a
critical listening training with respect to spatial audio attributes and ultimately design their own microphone
configuration for desired spatial imaging characteristics.
Keywords: Sound Recording, Microphone Technique, MARRS, Online teaching
1. Challenges in Sound Recording Education
Spatial acoustic recording technique using microphone arrays (i.e., stereo to multichannel) is an
important curriculum in sound recording education. There are a number of variables to consider in
order to achieve desired spatial characteristics, e.g., spacing and subtended angle between
microphones, microphone polar pattern, microphones’ height from the floor and distance from the
sound sources, etc. Furthermore, optimal settings of such variables would depend on contextual
factors such as the type of musical performance and the acoustic conditions of the recording venue.
Thus, making right decisions in terms of microphone array configuration and placement would require
not only practical experiences and musical understanding but also theoretical knowledge in spatial
audio psychoacoustics.
It is observed that recording engineers often make stereo recordings using famous microphone
configurations such as spaced omnis with 50cm spacing (AB), coincident XY with 90° subtended
angle, ORTF, NOS, Decca Tree, etc. Although such “preset” configurations can be a good starting
point, it is important to understand that all of them were devised in specific contexts and aims, and
they could not be applied in the same ways in all recording situations. Stereo imaging offered by a
specific configuration would primarily depend on the source-to-microphone distance, which should
be determined based on the desired spatial perspective (e.g., conductor or audience) and the acoustic
characteristics of the recording venue (e.g., reverberation time, early reflection energy, etc.).
Especially in education, it is crucial for students to learn fundamental principles behind different
microphone techniques and a systematic process to realize their artistic goal more effectively and
efficiently. Blindly using a popular configuration without understanding might lead them to rely on
luck for the outcome. Customizing or designing a microphone array to achieve a desired goal by
random trials and errors might cost a significant amount of time, but the result may not be reproducible
in other conditions. However, best practices built upon systematic approaches based on principles
would make them more versatile engineers who can adopt to various recording scenarios flexibly.
2. Online Teaching using MARRS for Web
Putting theory into practice in sound recording obviously requires students to go through practical
1
h.lee@hud.ac.uk
experimentations with musical ensembles in an acoustic space using microphones. However, this
would have been made difficult or impossible due to the COVID-19 restrictions. To overcome this
and carry on with teaching spatial recording techniques in the undergraduate Music Technology course
at the University of Huddersfield during two academic terms in 2020 and 2021, we updated and
utilized the MARRS for Web (https://marrsweb.hud.ac.uk/), which is the web application of the
MARRS (Microphone Array Recording and Reproduction Simulator), for online teaching of the
spatial recording module. MARRS was originally developed as iOS and Android apps (1), and the
initial Web version of the tool was introduced in (2), where technical details of the psychoacoustic
algorithm used and web audio implementation can be found.
MARRS for Web is an interactive tool that provides both audio (stereo and binaural) and visual
presentations of perceived sound image positions as well as the calculations of interchannel time and
level differences in real-time depending on the user’s microphone array settings. The tool was used
not only for teaching staff to demonstrate the psychoacoustic principles of various microphone
techniques, but also for the students to virtually experimenting with microphone settings and
eventually design their own configurations. MARRS for Web includes the following features.
• The user can change the horizontal and vertical positions of the sound sources and the
microphone array, in the top and side stage views of a virtual quartet.
• Microphone configuration is fully customizable (polar pattern, spacing, angle, height, vertical
tilting (pitch), distance).
• The perceived image positions of the sources are predicted depending on the user microphone
setting and interactively displayed in the speaker view.
• Stereo and binaural outputs for auditioning: anechoic string quartet recordings are provided by
default, but the user can also load other wave files. Each source can be muted or soloed.
• Convolution reverb with a level control is provided for simulating an acoustic space. A set of
stereo room impulse responses (RIRs) are provided, but the user can also load their own RIRs.
• The graph mode displays interchannel time and level differences and localization curve for a
given user microphone configuration.
Figure 1. The Stage and Graph modes in MARRS for Web https://marrsweb.hud.ac.uk/
MARRS for Web was found to be highly useful for students to virtually make recordings using
simulated microphone techniques during the pandemic period. In the post-pandemic era too, it will
continue to serve as a tool that students can use to consolidate their understanding about underlying
psychoacoustic principles of stereophonic recording in an interactive manner through visualization
and auditioning. Students will go through a series of controlled experimental recording sessions with
a virtual musical ensemble in a concert hall, where they try various microphone settings based on the
simulations provided by MARRS for Web, and critically listen to the recordings to discuss pros and
cons of each approach. Using such an assistive tool would allow for more effective and efficient
problem solving in sound recording. However, it is strongly encouraged for students to learn the
theoretical principles first rather than blindly relying on the result that the simulation provides.
REFERENCES
1. Lee H, Johnson D, Mironovs M, An interactive and intelligent tool for microphone array design, Proc
143rd AES Int Conv, Oct 2017. e-Brief 390.
2. Goddard N, Lee H, A web-based tool for microphone array design and phantom image prediction using
the web audio API, Proc 146th AES Int Conv, Mar 2019, e-Brief 499.