Real-time auralisation system for virtual microphone positioning

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 mi- crophone 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 sub- convolutions 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 la- tency) 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.
Fundação para a Ciência e a Tecnologia (FCT)