Why things don't work: What you need to know about spatial audio

ï~~Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011 WHY THINGS DON'T WORK: WHAT YOU NEED TO KNOW ABOUT SPATIAL AUDIO Gary S. Kendall Sonic Arts Research Center Queen's University Belfast [email protected] ABSTRACT Composers engaged in the sonic arts have frequently found themselves attempting to use spatial audio in ways that didn't work as intended. Maybe more than any other facet of technological music, mastering spatial audio seems to involve a learning process in which one slowly discovers the things that work and those that don't. The purpose of this paper is to foster understanding of spatial audio through examples of practical problems. These problems reveal some general misconceptions about spatial hearing that explain why things go wrong. A particular lesson to be gleaned from this discussion is that there is no silver bullet for solving spatial audio problems, and every situation needs to be understood in its proper context. 1. INTRODUCTION Composers engaged in the sonic arts have frequently found themselves attempting to use spatial audio in ways that didn't work as intended. Maybe more than any other facet of technological music, mastering spatial audio seems to involve a learning process in which one slowly discovers the things that work and those that don't. That this learning process is so tentative and empirical reflects the lack of a conceptual foundation that could guide the artist when conceiving spatial ideas and when translating these ideas into practice. It is also easy to be misled by preconceptions about how spatial audio should work. The purpose of this paper is to foster understanding of spatial audio through examples of practical problems. The early pioneers of electroacoustic music pushed the frontiers of spatial audio and achieved monumental successes in the artistic use of space. Varese, Stockhausen, Schaeffer and Poullin, Bayle with the Acousmonium, Chowning and onwards---spatial audio has been an expanding area of artistic expression. On the other hand, the great advantages in computer and audio technology that we enjoy today have not necessarily led to great advances in spatial audio. Quite possibly, pushing back the frontiers of spatial audio practice depends more on understanding spatial perception and cognition than on raw computing power. 2. GENERAL MISCONCEPTIONS In everyday life, every person is able to navigate the spatial world, to think about space and even to imagine unknown spaces; spatial thinking is one of our most deeply embedded cognitive capacities. The ease with 37 Andres Cabrera Sonic Arts Research Center Queen's University Belfast mantaraya36@ gmail.com which we think about space is possibly a miscue to how easily spatial ideas can be translated into spatial audio, which has its own intrinsic nature and inherent limitations. Sonic artists need to be alert to the nuances and idiosyncratic relationship of spatial hearing to spatial thinking. Not every spatial idea can be reverse engineered into sound. Clearly, our expectations about spatial audio should be in alignment with the fundamental capacities of the auditory system. For example, consider how auditory spatial acuity varies with the direction of the sound source. In front of the listener, horizontal localization blur is +3.6Â~, and to the sides it is Â~9-10o. Above the head and slightly to the rear, vertical localization blur is Â~22Â~ [3]. Apparently, what listeners perceive is not well described as a point source. More appropriately listeners' perceptions can be described in terms of a small set of auditory spatial attributes. Following work by Rumsey [16], Kendall [11] offered the image in Figure 1 as an illustration of these attributes. Depth/\ i Depth Height Width Figure 1. Auditory spatial attributes (from [11]). Important for spatial audio is the primary role of envelopment as a spatial attribute. Envelopment has been the focus much research in spatial audio [5, 20]. One of those idiosyncratic aspects of spatial audio is that there is no clear separation between auditory width and envelopment; one can blend into the other. 3. WHAT WENT WRONG? The way that most composers and audio engineers discover their misconceptions about spatial audio is through direct encounters with things that don't work. 3.1. Why doesn't the sound image get broader when I distribute a signal to three of more adjacent loudspeakers?