Archives of Acoustics, 34, 4, pp. 491-506, 2009

Application of Hilbert Transform-Based Methodology to Computer Modelling of Reverberant Sound Decay in Irregularly Shaped Rooms

Mirosław MEISSNER
Institute of Fundamental Technological Research, Polish Academy of Sciences

A study into the application of the Hilbert transform in
numerical simulations of reverberant sound decay in irregularly shaped
enclosures is presented. It is shown that there are some limitations in the use
of this integral transform to exponentially decaying harmonic signals because
the integration result consists not only of a signal, which differs from the
original one by a phase shift of [ampersand]pi;/2, but also of a decaying non-oscillating
signal occurring due to the fact that a spectrum of exponential function is
unbounded. An initial amplitude of this signal is directly proportional to the
ratio between a damping coefficient and a mode frequency, thus for lightly
damped rooms, where this ratio is much smaller than unity, it can be neglected.
Results of numerical simulation carried out for L-shaped enclosure indicate that
the Hilbert transform is a useful tool in calculating instantaneous properties
of reverberant sound, especially an envelope of the sound pressure level. It is
of special importance in the case of irregularly shaped rooms, where a deviation
from the exponential sound decay often occurs because of differences between
reverberant responses for particular modes.
Keywords: Hilbert transform; analytic signal; irregularly shaped enclosures; reverberant room response; reverberation time; early and late decay times
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