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Computer Simulations of Periodically Time-Varying Filters for Acoustic Feedback Control

Several modern systems for reverberation enhancement use time-varying electronic filters to increase their gain before instability (GBI). A computer simulation study is presented of systems with linear periodically time-varying (LPTV) filters based on an iterative frequency-domain method. Results are given from simulations and measurements of a single feedback loop with phase and delay modulators and feedback via an electronic reverberation unit. Comparison of measured and predicted values of GBI with a sinusoidal phase modulator showed deviations typically around 0.1 dB and at most 0.3 dB for modulation frequencies between 0.5 and 4 Hz and modulation indexes of up to 4.2 radians. Phase modulators displayed GBI improvements increasing almost monotonically with a modulation index up to 4.2 radians. Delay modulators gave slight improvement when used broad band, but when high-pass filtered at 600-Hz substantial improvements resulted with variations as low as ±0.5 ms. The detrimental effects of modulation in the form of audible amplitude and frequency fluctuations were studied as well.

Author: Svensson, Peter U.
Affiliation: Department of Applied Acoustics, Chalmers University of Technology, Gothenburg, Sweden
JAES Volume 43 Issue 9 pp. 667-677; September 1995 Import into BibTeX

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