Holographic auditory display and telepresence
The final goal of holographic audio is to offer an immersive auditory experience as if the listener is located in another environment. In this scenario, the sensation of the all auditory impressions should be consistent at multiple listener positions; the perceived location of sound sources, perceived stage width, even the sense of ambience should be identical to those experienced in another site.
(a) Target sound field
(b) Reproduced sound field
However, both the accurate evaluation and reproduction of multiple auditory impressions at multiple locations is nearly impossible. For this reason, sound field reproduction approaches devised to replicate the physical wave field of another environment have been useful. The current research on holographic auditory display, however, goes beyond the simple reproduction; How to design and create new sound fields that can provide new sensations? How can we reproduce sound fields that do not obey the laws of sound propagation?
[Concept of sound field reproduction]
This line of study deals with the creation/reproduction/manipulation of sound/wave fields in various shapes for holographic auditory displays and synthesis of high-dimensional auditory impressions. The underlying principle is simple interference of multiple wave fronts produced by multiple transducers/loudspeakers, but for the generation of a sound field in a desired shape, multi-dimensional aspects of a sound field should be considered in both the analysis and synthesis stages. Array signal processing techniques for controlling various objective and subjective variables in real-time constitute the core of this research field.
Sound field manipulation
> Sound field manipulation
Creation of artificial sound fields
Unlike the sound field reproduction that mainly focuses on the recreation of an existing sound field, it is also possible to create artificial sound fields rarely existing in natural conditions. The loudspeaker array can provide more degree of freedom in controlling the spatial distribution of sound, and hence, one can create a wholly new sound field with an aim of providing new auditory impressions or physical phenomena. For instance, perceived width of sound source can be arbitrarily manipulated depending on the position of a listener, or a sound hole/sink can be created to generate acoustic forces moving small particles to a specific location. The creation of new fields is possible through the aggressive amplification and control of higher order wave fields.
[Manipulation of perceived source width of a holographic object]