An Ambisonics Format for Flexible Playback Layouts

1st Ambisonics Symposium, 25-27 Juli, Graz, 2009

An Ambisonics Format for Flexible Playback Layouts

Ambisonics represents the sound field as a sum of angular modes (circular/spherical harmonics). The Ambisonics signals representing these angular modes are usually decoded to a set of loudspeakers by mode-matching equations. This works if the speakers are well-distributed on a circle or sphere. But Ambisonics playback arrangements frequently do not cover an entire circle or sphere due to practical constraints, which leads to non-trivial problems in decoder design. This paper presents two approaches to extend the capacities of Ambisonics to partial circular or spherical layouts by enabling decoder-design by mode-matching. The first approach selects suitable set of harmonics, based on their symmetry and periodicity, and works for some particular partial layouts. But these selections are difficult to use for playback on default loudspeaker layouts, i.e. a full circle/sphere, and are not applicable to arbitrary partial layouts. So finally, the paper presents a second approach, which provides full flexibility of partial layouts, while enabling playback on full default layouts. This favored second approach is driven by a reduced set of signals, which can be utilized to optimize the requirements for storage and transmission. The authors propose to store and transmit the reduced set of signals within a file exchange format that includes an appropriate reconstruction matrix.