1. S. Graetzer, E. J. Hunter and P. Bottalico
Vocal Comfort and Effort in Speech: Accommodation to Different Room Acoustic Conditions
5aSC15
S. Graetzer, E. J. Hunter and P. Bottalico
Dept. of Communicative Sciences and Disorders, Michigan State University, East Lansing, MI
Abstract
Method
Discussion
Vocal effort is a physiological entity that accounts for variation in voice production as loading increases, measured as sound pressure level (SPL). A number of studies have investigated vocal effort and load, but few have considered the role of acoustic clarity (C50), the early-to-late arriving sound energy ratio. In this study, 20 subjects performed vocal tasks in various room acoustic conditions in soft, normal, and loud styles. C50 in the position of the talker was changed by means of two acrylic glass panels. Two noise levels were used: background noise, and artificial child babble noise. After each task, the subject answered questions addressing their perception of vocal comfort, control and fatigue. SPL was measured. It was found that self-reported comfort and control tended to increase when panels were present, especially in the babble condition and in loud speech. SPL decreased when panels were present. The results indicate that even while keeping reverberation time constant, reflective surfaces may be used to increase voice comfort and reduce vocal effort.
10 M and 10 F y. subjects with normal speech and hearing read a text at different volumes in different room acoustic conditions. After each task, subjects responded to 3 questions: Q1: How fatigued would your voice be if you were to speak continuously in this condition for 20 minutes? Q2: How comfortable was it to speak in this condition? Q3: How well were you able to control your voice in this condition? See Fig. 1. Visual analogue scales, 10cm. Room acoustics assessed measuring the IRs generated by balloon pops (Fig.2 reports the Reverberation Time). IRs measured with KEMAR 45BB-1 HATS (mouth-ears) were used to quantify the effect of the panels (C50; Fig. 3). C50 modified by introducing reflective Plexiglas panels at 1m at 45⁰ on-axis. Speakers exposed to 60 dB child babble noise during half of the tasks (babble, randomized; background noise: 40 dB). Three volumes or “styles” of speech: loud, normal, soft (but not a whisper). Recorded by head-mounted Glottal Enterprises M-80 omnidirectional mic and Behringer ECM. Roland R-05 Wave digital recorder. Sound board: Scarlett 2i4 Focusrite. Recording software: Audacity. Analysis conducted in Aurora, MATLAB and R.
RQ1: In the loud vs. normal style, self-reported comfort and control decreased, while fatigue increased. Comfort and control were greater when noise was absent. Fatigue was greater in the loud style, especially with noise. Soft vs. normal style was associated with lower comfort and control responses.
RQ2: To evaluate the effect of the first reflection on the talker, C50 was measured from the IR (HATS mouth-ears), i.e., how a subject might perceive his/her feedback was evaluated (see [2]). When panels were present, i.e., when C50 was increased within the frequency range associated with speech, subjects tended to adjust their responses: in normal and loud styles (without babble noise), fatigue tended to decrease with panels; in the loud style, comfort and control tended to increase with panels; while in babble noise, control tended to increase with panels.
RQ3: Across most noise and style conditions, SPL decreased - hence vocal effort decreased - when panels were present. Additionally, a Lombard Effect of 0.24 dB/dB was found, which is comparable to effects reported in the literature in laboratory settings [3].
Results
Fig. 2
Fig. 3
Background
Conclusions
Vocal effort: physiological entity accounting for changes in voice production when loading increases; measured as SPL. Vocal comfort: psychological entity; magnitude determined by those aspects that reduce vocal effort [1]. Vocal control: capacity to self- regulate vocal behavior.
Reflective surfaces may be used by speakers in communication environments to increase perceived vocal comfort and to decrease vocal effort. In particular, effective use of early reflections directed towards the speaker in the design phase of a room could facilitate a reduction of vocal effort. In classroom design standards [4], this effect is not considered. Classroom acoustics standards should address the issue of reflections towards speakers so that acoustics can be optimized for teachers and pupils.
Fig. 4
Fig. 5
Research Questions
RQ1: What are the effects of volume (style) and noise on self-reported vocal fatigue, comfort and control? RQ2: Does acoustic clarity (C50) have an effect on perception of vocal fatigue, comfort and control? RQ3: Does C50 have an effect on vocal effort, measured as the difference in SPL from normal speech behavior for each subject (ΔSPL; ISO-9921)?
References
Bottalico, P., & Astolfi, A. (2012). Investigations into vocal doses and parameters pertaining to primary school teachers in classrooms. JASA 131,
Brunskog, D. J., Gade, A. C., Ballester, G. P., & Calbo, L. R. (2009). Increase in vocal level and speaker comfort in lecture rooms. JASA 125,
Kryter, K. D. (1946). Effects of ear protective devices on the intelligibility of speech in noise. JASA 18,
ANSI/ASA S Part I American National Standard Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools, Part 1: Permanent Schools (ASA, Melville, NY, 2010).
Fig 1. Example of subject’s responses for a given task.
Parameter Start st cycle th cycle th cycle th cycle
Acknowledgements
Fig 2. Upper L: Reverberation time (RT) in sec. by frequency (Hz). Mean T20 values in the octave band ranging from 125 Hz to 8 kHz with JND.
Fig 3. Upper R: Effect of reflective panels on acoustic clarity (C50) in dB by frequency (Hz) measured by HATS: Panel (red) and No panel (blue).
Fig 4. Lower L: Self-reported fatigue (L), comfort (middle) and control (R) by style (Soft, Normal, Loud), panel and noise: Noise (red) and No noise (blue).
Fig 5. Lower R: Effect of panel (upper L), noise (upper R), style (lower L; Soft, Normal, Loud), and the interaction of style and noise (lower R) on ΔSPL (dB).
Thanks to Andrew Lee and Lauren Glowski for research assistance. Research was in part supported by the NIDCD of the National Institutes of Health under Award Number R01DC The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.