Development of an ambisonic guitar system GASP: Guitars with ambisonic spatial performance

Ambisonics, pioneered by Michael Gerzon (1977,1985), is a kernel-based 3D surround sound system. The encoding (recording or panning) of the audio is separated from the decoding (or rendering) of the audio to speaker feeds or, more recently, head tracked headphones (by binaurally decoding the Ambisonic sound field). Audio encoded in this way can be rendered to any number of speakers in almost any position in 3D space, as long as the positions of the speakers are known. Moreover, Ambisonics is a system optimised around a number of psycho-acoustic criteria which, when implemented, reduce the variability of audio no matter what speaker arrangement is used for reproduction. This allows for a `mix once' system where subsequent remixing is not necessary when replayed over different loudspeaker systems or headphones and allows for full 3D reproduction. The Ambisonics system is finally gaining some traction due to its use in Virtual Reality audio, using the ambiX standard (Nachbar et al. 2011) but few instruments exist that make use of this 3D spatial audio format, although previous studies into some aspects of the relationship between instruments, performance and spatialisation is available, for example, see Pysiewica and Weinzierl (2017), Graham and Bridges (2017), Bates (2010), Pukette (2007) and Graham (2012). The system combines custom and off-the-shelf hardware/software to create both a live performance Ambisonic guitar system, and virtual reality (VR) ready, binaural performance instrument. The system comprises of two aspects: firstly as an innovative audio project, fusing the musical with the technical, combining individual string timbralisation with Ambisonic surround sound. And secondly as an artistic musical project, providing alternative experimental surround sound production ideas for the guitarist and music producer, with potential applications in the Sound Arts world as well as commercial musical applications. This paper explores the possibilities of the Guitar as a spatial instrument detailing the technical and artistic processes involved in the production and live performance of the instrument.
Key features of the described system include: Multichannel hexaphonic guitar pickups facilitate the guitar system to process individual strings independently for both timbre and spatial location. Guitar production timbre and effects are achieved with Line 6 Helix commercial sound processing software for individual string timbralisation. Ambisonic surround-sound performance: spatial positioning is achieved using our own bespoke WigWare algorithms and can be heard over either an array of circular (2D) or spherical (3D) loudspeakers, alternatively the user can listen to the output with headphones using binaural implementation. Rhythmic gate-switching of individual strings, such that either simple or complex polyrhythms can be programmed or performed live across individual strings (producing similar results to a keyboard controlled arpeggiator).
‘Auditory Scenes’ have been developed for presenting combinations of individual string timbres, spatial, and rhythmic arpeggiator parameters.
The system can be applied to post-production sound manipulation, or as a real-time live Ambisonic performance instrument within a concert environment. These two categories can yield differing production possibilities. We have also identified potential applications for guitar training and education.