Physical task stress and speaker variability in voice quality

Abstract

The presence of physical task stress induces changes in the speech production system which in turn produces changes in speaking behavior. This results in measurable acoustic correlates including changes to formant center frequencies, breath pause placement, and fundamental frequency. Many of these changes are due to the subject's internal competition between speaking and breathing during the performance of the physical task, which has a corresponding impact on muscle control and airflow within the glottal excitation structure as well as vocal tract articulatory structure. This study considers the effect of physical task stress on voice quality. Three signal processingbased values which include (i) the normalized amplitude quotient (NAQ), (ii) the harmonic richness factor (HRF), and (iii) the fundamental frequency are used to measure voice quality. The effects of physical stress on voice quality depend on the speaker as well as the specific task. While some speakers do not exhibit changes in voice quality, a subset exhibits changes in NAQ and HRF measures of similar magnitude to those observed in studies of soft, loud, and pressed speech. For those speakers demonstrating voice quality changes, the observed changes tend toward breathy or soft voicing as observed in other studies. The effect of physical stress on the fundamental frequency is correlated with the effect of physical stress on the HRF (r = −0.34) and the NAQ (r = −0.53). Also, the inter-speaker variation in baseline NAQ is significantly higher than the variation in NAQ induced by physical task stress. The results illustrate systematic changes in speech production under physical task stress, which in theory will impact subsequent speech technology such as speech recognition, speaker recognition, and voice diarization systems.

Voice Stress Analysis: A New Framework for Voice and Effort in Human Performance

“…This timbre is the result of the combined output of the relative strength of the different subcomponents or harmonics of the sound that can be obtained by spectral analysis. A measure that gives insight into the general harmonic richness of a sound or voice quality is the harmonic richness factor (HRF) which refers to the ratio of the sum of the amplitudes of the harmonics and the amplitude of the component at the fundamental frequency ( Godin and Hansen, 2015 ). However, voice quality is not just a question of the amplitude mapping of the harmonics.…”

“…Some measures are based on a technique of inverse filtering to capture the activity of the glottal voice source waveform, the sound produced by the pulsating transglottal airflow. The aim of this procedure is to remove the effects of natural vocal tract filtering and to obtain information regarding the quality of phonation (e.g., Alku et al, 2002 ) or vice versa to gather the vocal tract signal ( Cummings and Clements, 1992 ) by measuring the duration and instant of glottal closure (e.g., Hansen, 1989 ; Godin and Hansen, 2015 ). The glottal waveform of a vowel, for instance, is a cycle of closed and open phases ( Godin and Hansen, 2015 ).…”

“…Concretely, an increased OCQ is indicative of a breathy voice whereas a decreased OCQ is related to a ‘pressed’ voice ( Alku and Vilkman, 1996 ). Another measure for ‘breathiness’ of the voice is the normalized amplitude quotient (NAQ) ( Alku and Vilkman, 1996 ; Alku et al, 2002 ; Campbell and Mokhtari, 2003 ; Godin and Hansen, 2015 ). NAQ is the ratio of the maximum peak-to-peak amplitude of the glottal flow to the minimum of the glottal flow derivative, normalized by the fundamental period and the sampling frequency ( Alku et al, 2002 ; Godin and Hansen, 2015 ).…”

“…Another measure for ‘breathiness’ of the voice is the normalized amplitude quotient (NAQ) ( Alku and Vilkman, 1996 ; Alku et al, 2002 ; Campbell and Mokhtari, 2003 ; Godin and Hansen, 2015 ). NAQ is the ratio of the maximum peak-to-peak amplitude of the glottal flow to the minimum of the glottal flow derivative, normalized by the fundamental period and the sampling frequency ( Alku et al, 2002 ; Godin and Hansen, 2015 ). In comparison with neutral speech, an increased NAQ indicates a breathy phonation, whereas a decreased NAQ is the result of a pressed phonation ( Alku et al, 2002 ; Godin and Hansen, 2015 ).…”

The physical basis of gesture-speech synchrony: Exploratory study and pre-registration

“…Given the essential and sensitive role of expiration-related muscles and alveolar pressure in the stable production of speech (more specifically phonation), we must wonder whether arm movements in the form of gestures could affect prosodic metrics of speech directly (e.g., contrasts in F0; changes in amplitude)? Despite studies that have looked at effects of gross body exercise during speaking and phonation (Godin & Hansen, 2015;Johaness et al, 2007) and further advanced research on phonation on a plethora of physical constraints on F0 modulation (e.g., breathing cycles, see Bouhuys, 1974;alveolar pressure and volume, Dromey & Ramig, 1998;heart beat cycles, Orlikoff & Baken, 1988), we are unaware of any research in phonetics that has looked at the possible biomechanical effects of upper limb movement and phonation that can be directly informative to gesture-speech dynamics.…”