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. 2024 Jan;38(1):1-9.
doi: 10.1016/j.jvoice.2021.08.004. Epub 2021 Oct 12.

Characterization of Source-Filter Interactions in Vocal Vibrato Using a Neck-Surface Vibration Sensor: A Pilot Study

Rosemary A Lester-Smith  1 , Elaina Derrick  2 , Charles R Larson  3
Affiliations

Characterization of Source-Filter Interactions in Vocal Vibrato Using a Neck-Surface Vibration Sensor: A Pilot Study

Rosemary A Lester-Smith et al. J Voice. 2024 Jan.

Abstract

Purpose: Vocal vibrato is a singing technique that involves periodic modulation of fundamental frequency (fo) and intensity. The physiological sources of modulation within the speech mechanism and the interactions between the laryngeal source and vocal tract filter in vibrato are not fully understood. Therefore, the purpose of this study was to determine if differences in the rate and extent of fo and intensity modulation could be captured using simultaneously recorded signals from a neck-surface vibration sensor and a microphone, which represent features of the source before and after supraglottal vocal tract filtering.

Method: Nine classically-trained singers produced sustained vowels with vibrato while simultaneous signals were recorded using a vibration sensor and a microphone. Acoustical analyses were performed to measure the rate and extent of fo and intensity modulation for each trial. Paired-samples sign tests were used to analyze differences between the rate and extent of fo and intensity modulation in the vibration sensor and microphone signals.

Results: The rate and extent of fo modulation and the extent of intensity modulation were equivalent in the vibration sensor and microphone signals, but the rate of intensity modulation was significantly higher in the microphone signal than in the vibration sensor signal. Larger differences in the rate of intensity modulation were seen with vowels that typically have smaller differences between the first and second formant frequencies.

Conclusions: This study demonstrated that the rate of intensity modulation at the source prior to supraglottal vocal tract filtering, as measured in neck-surface vibration sensor signals, was lower than the rate of intensity modulation after supraglottal vocal tract filtering, as measured in microphone signals. The difference in rate varied based on the vowel. These findings provide further support of the resonance-harmonics interaction in vocal vibrato. Further investigation is warranted to determine if differences in the physiological source(s) of vibrato account for inconsistent relationships between the extent of intensity modulation in neck-surface vibration sensor and microphone signals.

Keywords: Modulation; Source-filter; Vibrato.

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Conflict of interest statement

Declarations of Interest

None

Figures

Figure 1:
Figure 1:
Waveform (upper panel) and narrowband spectrogram (lower panel) for simultaneously recorded normalized microphone (left panel) and vibration sensor signals (right panel) for /ɑ/ with vibrato.
Figure 2:
Figure 2:
Results of the rate of fundamental frequency (fo) modulation analysis, with the microphone signal on the x-axis and the vibration sensor signal on the y-axis. The orange 1:1 line represents matched rates of fo modulation in the microphone and vibrato sensor signals.
Figure 3:
Figure 3:
Results of the extent of fundamental frequency (fo) modulation analysis, with the microphone signal on the x-axis and the vibration sensor signal on the y-axis. The orange 1:1 line represents matched extents of fo modulation in the microphone and vibration sensor signals.
Figure 4:
Figure 4:
Results of the rate of intensity modulation analysis, with the microphone signal on the x-axis and the vibration sensor signal on the y-axis. The orange 1:1 line represents matched rates of intensity modulation in the microphone and vibration sensor signals.
Figure 5:
Figure 5:
Results of the extent of intensity modulation analysis, with the microphone signal on the x-axis and the vibration sensor signal on the y-axis. The orange 1:1 line represents matched extents of intensity modulation in the microphone and vibration sensor signals.
Figure 6:
Figure 6:
Illustration of the relationship between the difference in the rate of intensity modulation in the microphone and vibration sensor signals and the typical difference in F1 and F2 based on Peterson & Barney (1952).
See this image and copyright information in PMC

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