irregular,ambisonics,ITU 775

Eridanus is a 40-minutes-long sci-fi thriller story told through Spatial audio technologies and applied psychoacoustics, using a bespoke 21.4 array of speakers. In a dark black room, an audience of four people is able to experience the performance at one time.

This research and body of work explores how Spatial Audio can be used as a tool for storytelling. There are various media that tell stories relying only on sound, such as radio drama, audio books, and sound installations. These involve different conceptual and technological approaches that allow stories to be told in different ways, such as the use of narration to describe how characters feel, or the environment where they are in. By taking inspiration from Virtual Reality and its 360 degree viewpoint available, this project explores how, using only 360 degree audio, or immersive audio, technically called Spatial Audio, a story can be told.
After an analysis of various forms of digital media and how they use sound to convey meaning, an hybrid narrative format is created, with the aim of realising an entertaining piece of work.

Different Spatial Audio techniques and tools are available for practical use, and various sonic aspects can be used with these, such as the creation of convincing and immersive soundscapes, characters’ ‘sound shapes’, and emotions triggering with sound localisation.

The project involves the development of an original story, building a custom loudspeaker array, an advanced workflow for object-based mixing creation, pre-production, spatial sound design, recording, mixing and presentation.

Currently, the ITU standard surround sound speaker arrangement is based on an irregular 5 speaker array.  However, this may change to an irregular 7 speaker array (as is now the standard on computer hardware) or more in the future.  The Ambisonic system, pioneered by Micheal Gerzon, among others, in the late 1960’s, is very well suited to situations where the end system speaker configuration is not fixed in terms of number or position while also offering a simple way (via energy and velocity vector analysis) of quantifying the performance of such systems.  However, while the derivation of the decoders is well documented for regular speaker arrangements [1], optimising the decoders for irregular layouts is not a simple task, where optimisation requires the solution of a set of non linear simultaneous equations, complicated further by the fact that multiple solutions are possible [2].  Craven [3] extended the system to use higher order circular harmonics and presented a 4th order Ambisonic decoder (9 input channels), although the derivation method used was not presented. 

In this paper a semi-automated decoder optimisation system using heuristic methods will be presented that will be shown to be robust enough to generate higher order Ambisonic decoders based on the energy and velocity vector parameters.  This method is then analytically compared to Craven’s decoder using both energy/velocity vector and head related transfer function based methods.


[1] Gerzon, M.A. (1985) Ambisonics in Multichannel Broadcasting and Video.  Journal of the Audio Engineering Society, Vol. 33, No. 11, p. 851-871.
[2] Gerzon, M. A. & Barton, G. J. (1992) Ambisonic Decoders for HDTV.  Proceedings of the 92nd International AES Convention, Vienna. 24 – 27 March. Preprint 3345.
[3] Craven, P. (2003), Continuous Surround Panning for 5-speaker Reproduction, AES 24th International Conference, Banff, Canada.