A computer application was developed to simulate the process of microphone positioning in sound recording applications. A dense, regular grid of impulse responses pre-recorded on the region of the room under study allowed the sound captured by a virtual microphone to be auralised through real-time convolution with an anechoic stream representing the sound source. Convolution was performed using a block-based variation on the overlap-add method where the summation of many small subconvolutions produced each block of output data samples. As the applied RIR filter varied on successive audio output blocks, a short cross fade was applied to avoid glitches in the audio. The maximum possible length of impulse response applied was governed by the size of audio processing block (hence latency) employed by the program. Larger blocks allowed a lower processing time per sample. At 23.2ms latency (1024 samples at 44.1kHz), it was possible to apply 9 second impulse responses on a standard laptop computer.

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This paper describes a software package for auralisation in interactive virtual reality environments. Its purpose is to reproduce, in real time, the 3D soundfield within a virtual room where listener and sound sources can be moved freely. Output sound is presented binaurally using headphones. Auralisation is based on geometric acoustic models combined with head-related transfer functions (HRTFs): the direct sound and reflections from each source are computed dynamically by the image-source method. Directional cues are obtained by filtering these incoming sounds by the HRTFs corresponding to their propagation directions relative to the listener, computed on the basis of the information provided by a head-tracking device. Two interactive real-time applications were developed to demonstrate the operation of this software package. Both provide a visual representation of listener (position and head orientation) and sources (including image sources). One focusses on the auralisation-visualisation synchrony and the other on the dynamic calculation of reflection paths. Computational performance results of the auralisation system are presented.

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