Effects of Low-Pass Filtering on Acoustic Analysis of Voice

Abstract

Objective/Hypothesis-Low-pass filtering is often applied to eliminate effects of environmental noise when preparing voice recordings for acoustic analysis. This study tested the effects of low-pass filter cutoff frequency on the results of acoustic voice analysis, with a particular interest in the effects of low cutoff frequencies on nonlinear dynamic parameters.Study Design-A crossover randomized controlled trial was performed using voice recordings of sustained vowel phonation obtained from the Disordered Voice Database.Methods-A second-order Butterworth filter was applied to the voices at cutoff frequencies ranging from 5000 to 40Hz. Percent jitter, percent shimmer, fundamental frequency (F 0 ), signalto-noise ratio (SNR), D 2 , and K 2 were calculated for each signal.Results-Traditional acoustic parameters were validly measured at cutoff frequencies as low as 300Hz. SNR and percent shimmer were improved by cutoff frequencies of 300Hz or higher; F 0 and percent jitter were unaffected by filtering at these frequencies. D 2 and K 2 were measured stably for signals filtered at cutoff frequencies as low as 100Hz.Conclusion-To ensure accuracy in acoustic voice analysis, setting the cutoff frequency of a low-pass filter at least one octave above the fundamental frequency (minimum of 300Hz) is recommended. Nonlinear dynamic measures of correlation dimension (D 2 ) and second-order entropy (K 2 ) proved more robust and maintained accuracy at lower frequencies.

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“…This signal editing was performed by a single speech therapist who was not offering clinical services to the participants. The Ac signals were analyzed for calculation of a 5-point period perturbation quotient (PPQ) and an 11-point amplitude perturbation quotient (APQ) after applying low-pass filtering at 10,000 Hz [14], using the Praat software package [15]. …”

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