Realistisk formidling af virtuelle lydkilder - 4-to-one

nyttigt af have teknikker til troværdig formidling af lydens rumlige karakter med i vores værktøjskasse.
Det bliver spændende at følge, hvad der sker på området i de kommende år.
English summary
English title: Realistic mediation of virtual sound sources. An experimental exploration of binaural synthesis
and head tracking, and of how this combination can be used in a system for communication of realistic 3D
sound.
Since the first systems for storing and playing back sound were invented in the second half of the 19th
century, we have become increasingly better at reproducing sound, resulting in an increasing degree of
fidelity. However, we still have difficulties reproducing the spatial properties of a sound phenomenon –
the experience of the exact spatial location of the individual sound sources.
This paper describes the development of a system that aims at doing exactly this. It uses binaural syn-
thesis, head tracking and acoustics simulation in an attempt to create a realistic sense of the spatiality of
sound played though headphones – this, within an experience-oriented context. It is not the first system
of its kind. These technologies have been combined before in different systems for reproducing 3D
sound for different purposes. The system described in this paper is based on the knowledge and experi-
ences gained in the development of such similar systems. However, I also hope to be able to present
solutions and experiences that might be a help to any future work in this area.
The following is a dense summary of the system’s construction and functionality.
The system is built in the programming environment Max, also known as Max/MSP 78 .
The binaural synthesis is based on convolution with impulse responses from the CIPIC HRTF database 79 .
Inspired by the article, Rendering Localized Spatial Audio in a Virtual Auditory Space 80 , it was decided to per-
form the convolution in the frequency domain, since this is ‘cheaper’ than time domain convolution pro-
cessor-wise. The impulse responses from the CIPIC database were, beforehand, interpolated in Matlab 81 ,
by first aligning the responses in time, and then interpolating (still in the time domain). The cropped time
delay of each impulse response is saved separately and re-implemented real-time (after convolution)
where an interpolation is performed on this parameter. Then the responses were then converted to the
frequency domain via FFT (so that this should not be done real-time) with a FFT size of 2048 and ex-
ported to Max. In Max, the data of a given CIPIC subject is ‘held’ by jit.matrix objects. The binaural syn-
78 http://cycling74.com
79 http://interface.cipic.ucdavis.edu/sound/hrtf.html
80 Zotkin, Duraiswami, and Davis.
81 http://www.mathworks.se/products/matlab/index.html
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