Speakers' comfort and voice level variation in classrooms: laboratory research

Teachers adjust their voice levels under different classroom acoustics conditions, even in the absence of background noise. Laboratory experiments have been conducted in order to understand further this relationship and to determine optimum room acoustic conditions for speaking. Under simulated acoustic environments, talkers do modify their voice levels linearly with the measure voice support, and the slope of this relationship is referred to as room effect. The magnitude of the room effect depends highly on the instruction used and on the individuals. Group-wise, the average room effect ranges from -0.93 dB/dB, with free speech, to -0.1 dB/dB with other less demanding communication tasks as reading and talking at short distances. The room effect for some individuals can be as strong as -1.7 dB/dB. A questionnaire investigation showed that the acoustic comfort for talking in classrooms, in the absence of background noise, is correlated to the decay times derived from an impulse response measured from the mouth to the ears of a talker, and that there is a maximum of preference for decay times between 0.4 and 0.5 s. Teachers with self-reported voice problems prefer higher decay times to speak in than their healthy colleagues.     

Equal autophonic level curves under different room acoustics conditions

The indirect auditory feedback from one's own voice arises from sound reflections at the room boundaries or from sound reinforcement systems. The relative variations of indirect auditory feedback are quantified through room acoustic parameters such as the room gain and the voice support, rather than the reverberation time. Fourteen subjects matched the loudness level of their own voice (the autophonic level) to that of a constant and external reference sound, under different synthesized room acoustics conditions. The matching voice levels are used to build a set of equal autophonic level curves. These curves give an indication of the amount of variation in voice level induced by the acoustic environment as a consequence of the sidetone compensation or Lombard effect. In the range of typical rooms for speech, the variations in overall voice level that result in a constant autophonic level are on the order of 2 dB, and more than 3 dB in the 4 kHz octave band. By comparison of these curves with previous studies, it is shown that talkers use acoustic cues other than loudness to adjust their voices when speaking in different rooms.     

Comment on "Increase in voice level and speaker comfort in lecture rooms" [J. Acoust. Soc. Am. 125, 2072-2082 (2009)] (L)

Recently, a paper written by Brunskog Gade, Paya?-Ballester and Reig-Calbo, "Increase in voice level and speaker comfort in lecture rooms" [J. Acoust. Soc. Am. 125, 2072-2082 (2009)] related teachers' variation in vocal intensity during lecturing to the room acoustic conditions, introducing an objective parameter called "room gain" to describe these variations. In a failed attempt to replicate the objective measurements by Brunskog et al., a simplified and improved method for the calculation of room gain is proposed, in addition with an alternative magnitude called "voice support." The measured parameters are consistent with those of other studies and are used here to build two empirical models relating the voice power levels measured by Brunskog et al., to the room gain and the voice support.     

Reverberation time and maximum background-noise level for classrooms from a comparative study of speech intelligibility metrics

Speech intelligibility metrics that take into account sound reflections in the room and the background noise have been compared, assuming diffuse sound field. Under this assumption, sound decays exponentially with a decay constant inversely proportional to reverberation time. Analytical formulas were obtained for each speech intelligibility metric providing a common basis for comparison. These formulas were applied to three sizes of rectangular classrooms. The sound source was the human voice without amplification, and background noise was taken into account by a noise-to-signal ratio. Correlations between the metrics and speech intelligibility are presented and applied to the classrooms under study. Relationships between some speech intelligibility metrics were also established. For each noise-to-signal ratio, the value of each speech intelligibility metric is maximized for a specific reverberation time. For quiet classrooms, the reverberation time that maximizes these speech intelligibility metrics is between 0.1 and 0.3 s. Speech intelligibility of 100% is possible with reverberation times up to 0.4-0.5 s and this is the recommended range. The study suggests "ideal" and "acceptable" maximum background-noise level for classrooms of 25 and 20 dB, respectively, below the voice level at 1 m in front of the talker.     

Acoustic Prediction of Voice Type in Women with Functional Dysphonia

The categorization of voice into quality type (ie, normal, breathy, hoarse, rough) is often a traditional part of the voice diagnostic. The goal of this study was to assess the contributions of various time and spectral-based acoustic measures to the categorization of voice type for a diverse sample of voices collected from both functionally dysphonic (breathy, hoarse, and rough) (n=83) and normal women (n=51). Before acoustic analyses, 12 judges rated all voice samples for voice quality type. Discriminant analysis, using the modal rating of voice type as the dependent variable, produced a 5-variable model (comprising time and spectral-based measures) that correctly classified voice type with 79.9% accuracy (74.6% classification accuracy on cross-validation). Voice type classification was achieved based on two significant discriminant functions, interpreted as reflecting measures related to "Phonatory Instability" and "F(0) Characteristics." A cepstrum-based measure (CPP/EXP ratio) consistently emerged as a significant factor in predicting voice type; however, variables such as shimmer (RMS dB) and a measure of low- vs. high-frequency spectral energy (the Discrete Fourier Transformation ratio) also added substantially to the accurate profiling and prediction of voice type. The results are interpreted and discussed with respect to the key acoustic characteristics that contributed to the identification of specific voice types, and the value of identifying a subset of time and spectral-based acoustic measures that appear sensitive to a perceptually diverse set of dysphonic voices.     

Evaluation of acoustical conditions for speech communication in working elementary school classrooms

Detailed acoustical measurements were made in 41 working elementary school classrooms near Ottawa, Canada to obtain more representative and more accurate indications of the acoustical quality of conditions for speech communication during actual teaching activities. This paper describes the room acoustics characteristics and noise environment of 27 traditional rectangular classrooms from the 41 measured rooms. The purpose of the work was to better understand how to improve speech communication between teachers and students. The study found, that on average, the students experienced: teacher speech levels of 60.4 dB A, noise levels of 49.1 dB A, and a mean speech-to-noise ratio of 11 dB A during teaching activities. The mean reverberation time in the occupied classrooms was 0.41 s, which was 10% less than in the unoccupied rooms. The reverberation time measurements were used to determine the average absorption added by each student. Detailed analyses of early and late-arriving speech sounds showed these sound levels could be predicted quite accurately and suggest improved approaches to room acoustics design.     

Acoustic analysis of voice in individuals with amyotrophic lateral sclerosis and perceptually normal vocal quality

Currently, early phonatory changes in amyotrophic lateral sclerosis(ALS) are not well understood. The aim of this study was to compare acoustic parameters of voice in ALS subjects who demonstrated perceptually normal vocal quality on sustained phonation with a control group. We hypothesized that objective analysis of voice would reveal significant differences on specific acoustic parameters of voice compared to the control group. Results revealed statistically significant differences between the two groups on measures related to frequency range and phonatory stability. The findings suggest that early bulbar signs affecting the laryngeal system may be present in patients with ALS before the occurrence of perceptually aberrant vocal characteristics.     

Adverse Effects of Environmental Noise on Acoustic Voice Quality Measurements

An accurate analysis of voice quality is imperative when using acoustic measurements to diagnose vocal pathologies. It is known that noise has a significant effect on the reliability and validity of acoustic voice measurements, but the precise relationship has not been established. The purpose of this study was to investigate the influence of noise on the accuracy, reliability, and validity of acoustic voice quality measurements while balancing for gender, age, intersubject and intrasubject variability, microphones, computer hardware, analysis software, and type of noise. Level of noise was precisely controlled. The specific focus of interest was to determine the critical levels of noise that can invalidate voice quality measurements and to generate practical recommendations. Results suggest that the recommended, acceptable, and unacceptable levels of noise in the acoustic environment are above 42 dB, above 30 dB, and below 30 dB signal-to-noise ratio, respectively.     

Indoor Noise Reduction Index with an open window (Part II)

An index to evaluate indoor noise level reduction with an open window Noise Reduction Index (NRI) was proposed [Buratti C. Indoor Noise Reduction Index with open window. Appl Acoust 2002;63(4):431-51]. The reduction was due to the installation of a false ceiling in the room, thus reducing the contribution of the reverberant field. Experimental data related to two different kinds of false ceiling were compared to the results obtained by an original calculation model. Good agreement was found between experiments with two different materials and predictions. The present paper examines six different kinds of false ceiling and arrives at a new validation of the model. Calculations of NRI show good agreement with experimental data: a maximum difference of −1.2 dB(A) was found with a mean difference of 0.5 dB(A) for a wide range of absorption coefficient values. Hence the model represents a reliable instrument for indoor NRI prediction, if the acoustic absorption characteristics of materials are known.     

Rating,ranking, and understanding acoustical quality in university classrooms

Nonoptimal classroom acoustical conditions directly affect speech perception and, thus, learning by students. Moreover, they may lead to voice problems for the instructor, who is forced to raise his/her voice when lecturing to compensate for poor acoustical conditions. The project applied previously developed simplified methods to predict speech intelligibility in occupied classrooms from measurements in unoccupied and occupied university classrooms. The methods were used to predict the speech intelligibility at various positions in 279 University of British Columbia (UBC) classrooms, when 70% occupied, and for four instructor voice levels. Classrooms were classified and rank ordered by acoustical quality, as determined by the room-average speech intelligibility. This information was used by UBC to prioritize classrooms for renovation. Here, the statistical results are reported to illustrate the range of acoustical qualities found at a typical university. Moreover, the variations of quality with relevant classroom acoustical parameters were studied to better understand the results. In particular, the factors leading to the best and worst conditions were studied. It was found that 81% of the 279 classrooms have "good," "very good," or "excellent" acoustical quality with a "typical" (average-male) instructor. However, 50 (18%) of the classrooms had "fair" or "poor" quality, and two had "bad" quality, due to high ventilation-noise levels. Most rooms were "very good" or "excellent" at the front, and "good" or "very good" at the back. Speech quality varied strongly with the instructor voice level. In the worst case considered, with a quiet female instructor, most of the classrooms were "bad" or "poor." Quality also varies with occupancy, with decreased occupancy resulting in decreased quality. The research showed that a new classroom acoustical design and renovation should focus on limiting background noise. They should promote high instructor speech levels at the back of the classrooms. This involves, in part, limiting the amount of sound absorption that is introduced into classrooms to control reverberation. Speech quality is not very sensitive to changes in reverberation, so controlling it for its own sake should not be a design priority.     

The room acoustic rendering equation

An integral equation generalizing a variety of known geometrical room acoustics modeling algorithms is presented. The formulation of the room acoustic rendering equation is adopted from computer graphics. Based on the room acoustic rendering equation, an acoustic radiance transfer method, which can handle both diffuse and nondiffuse reflections, is derived. In a case study, the method is used to predict several acoustic parameters of a room model. The results are compared to measured data of the actual room and to the results given by other acoustics prediction software. It is concluded that the method can predict most acoustic parameters reliably and provides results as accurate as current commercial room acoustic prediction software. Although the presented acoustic radiance transfer method relies on geometrical acoustics, it can be extended to model diffraction and transmission through materials in future.     

Work-Related Communicative Profile of Voice Teachers: Effects of Classroom Noise on Voice and Hearing Abilities

PurposeVocal instructors during their normal workday are exposed to high noise levels that can affect their voice and hearing health. The goal of this study was to evaluate the voice and hearing status of voice instructors before and after lessons and relate these evaluations with voice and noise dosimetry taken during lessons.MethodsEight voice instructors volunteered to participate in the study. The protocol included (1) questionnaires, (2) pre/post assessment of voice quality and hearing status, and (3) voice and noise dosimetry during lessons. Acoustic measurements were taken of the unoccupied classrooms.ResultsIn six of eight classrooms, the measured noise level was higher than the safety recommendations set by National Institute for Occupational Safety and Health. The background noise level and the reverberation time in the classrooms were in compliance with the national standard recommendations. We did not find a clear pattern comparing pre- and post-measurements of voice quality consistent among genders. In all subjects, the Sound Pressure Levels mean increased, and the standard deviation of fundamental frequency decreased indicating association to vocal fatigue. Previous studies link these changes to increasing vocal fatigue. The audiometric results revealed seven out of eight instructors have sensorineural hearing loss.ConclusionsThe interaction of the acoustic space and noise levels can contribute to the development of hearing and voice disorders for voice instructors. If supported by larger sample size, the results of this pilot study could justify the need for a hearing and voice conservation program for music faculty.     

Influence of Data Acquisition Environment on Accuracy of Acoustic Voice Quality Measurements

Accuracy of acoustic voice analysis is influenced by the quality of recording. Lately, articles have suggested that soundcards perform equivalently to specialized professional-grade data acquisition (DA) systems. The purpose of this study was to investigate the influence of DA environment (DA system and microphone) on acoustic voice quality measurement (VQM) while balancing for gender, age, intersubject and intrasubject variability, and analysis software. More specifically, the relative performance of different hardware environments and the relationship between their technical characteristics and VQM performance was investigated. The discretization error and the effective dynamic range of the different DA environments were measured. We used 3 software systems to record and measure separately 2000 acoustic samples of sustained phonation for fundamental frequency, jitter, and shimmer. Analyses of variance (ANOVA) were performed with these parameters as the dependent variables. The results of the study suggested that professional-grade DA hardware is strongly recommended to provide accurate and valid voice assessment. The fundamental frequency measurement differences across DA environments were highly correlated to the discretization error (r=1.00), whereas jitter and shimmer were highly correlated to the effective dynamic range of the DA environments (r=-0.68 and r=-0.86, respectively).     

Acoustical Aspects of Vocal Function Following Radiotherapy for Early T1a Laryngeal Cancer

We evaluated acoustic voice characteristics of 18 male patients undergoing radiotherapy. The subjects were seen for voice assessment preradiotherapy and at 1 month, 3 months, 6 months, and 1 year following radiotherapy. A multidimensional voice analysis computer program (IVANS, Avaaz Innovations, 1998) was employed to evaluate measures of traditional frequency and amplitude perturbation as well as time-based and linear prediction (LP) modeled "noise" parameters of the acoustic output in conjunction with perceptual judgments of overall vocal quality. The results indicate vocal deterioration of vocal function immediately following radiotherapy with gradual and significant improvement in acoustic and perceptual features over 9 to 12 months following the radiation treatment. Measures of glottal noise demonstrated higher sensitivity than frequency-based measures of voice perturbation, and with more consistent, less variable changes in acoustical voice output from the preradiation to the 12 month postradiation periods. Future research evaluating vowel type and acoustic perturbation measures with a larger sample of subjects over a longer time period seems warranted.     

Comparison between measured and calculated parameters for the acoustical characterization of small classrooms

This paper presents a comparison between measured and calculated acoustical parameters in eight high school classrooms. The mid frequency unoccupied and occupied reverberation times and the 1 kHz sound propagation (SP) of the reverberant and total speech levels in occupied classrooms were compared with analytical and numerical predictions. The ODEON 6.5 code and the Sabine formula gave the most accurate results for reverberation time in the empty classrooms with overall relative differences of 8.1% and 9.7%, respectively. With students present, the Eyring and Sabine formulas and Hodgson’s empirical model resulted to be the most accurate with relative differences of 11.1%, 13.2% and 13.6%, respectively. The reverberant speech levels decrease with increasing distance from the source at rates varying from −1.21 to −2.62 dB/distance doubling, and the Hodgson model fits the slope values quite well. The best predictions of the SP of the reverberant and total speech levels are shown, in order of accuracy, for the ODEON code, the Barron and Lee theory and the classical diffuse field theory. Lower rms errors were found when the measured total acoustic absorptions were used. The lowest rms error of 1.4 dB for the SP of the total speech level were found for both the ODEON code and the Barron and Lee theory.     

Evaluation of Voice Pathology Based on the Estimation of Vocal Fold Biomechanical Parameters

Voice disorders are a source of increasing concern as normal voice quality is a social demand for at least one third of the population in developed countries in cases where voice is an essential resource in professional exercise. In addition, the growing exposure to certain pathogenic factors such as smoking, alcohol abuse, air pollution, and acoustic contamination, and other problems such as gastro-esopharyngeal reflux or allergy as well as aging, aggravate voice disorders. Voice pathologies justify the assignment of larger resources to prevention policies, early detection, and less aggressive treatments. Traditional pathology detection relies on perceptive evaluation methods (GRABS), acoustic analysis, and visual inspection (indirect laryngoscopy, and modern fibro-endo-stroboscopy). This article describes a method for voice pathology detection based on the noninvasive estimation of vocal cord biomechanical parameters derived from voice using specific signal processing methods. Preliminary results using records from patients showing four frequent causes of voice pathology (nodules, polyps, chronic laryngitis, and Reinke's edema) are given. The results show that the alteration (distortion, unbalance, or deviation) of cord biomechanical parameters may serve as an indicator of pathology. Statistical methods based on hierarchical clustering and principal component analysis reveal that combining biomechanical estimates with classic perturbation parameters increases the accuracy of acoustic analysis, improving the detection of voice pathology. This research could open new possibilities for noninvasive screening of vocal fold pathologies and could be used in the implantation of e-health voice care services.     

Self-to-other ratios measured in an opera chorus in performance

Four volunteer members of the chorus of Opera Australia, representing four different voice categories, wore binaural pairs of wireless microphones during a penultimate dress rehearsal on the Opera Theater stage of the Sydney Opera House. From the recordings, data were obtained on sound levels and on the self-to-other ratios (SORs). The sound levels were comparable to those found in loud music in chamber choir performance. The average SOR ranged from +10 to +15 dB. Compared to chamber choirs in other types of room, the SOR values were high. On a separate occasion, the stage support parameters ST1 (early reflections) and ST2 (late reflections) were measured over the whole stage area. ST1 was about -16 dB, which is typical for opera stages, and -20 dB for ST2, which is unusually low. It is concluded that the SOR in the opera chorus depends mostly on choir formation, which is highly variable, and that an opera chorus artist generally can hear his or her own voice very well, but little of the others and of the orchestra. This was confirmed by informal listening to the recordings.     

Perceptual sensitivity to first harmonic amplitude in the voice source

Little is known about the perceptual importance of changes in the shape of the source spectrum, although many measures have been proposed and correlations with different vocal qualities (breathiness, roughness, nasality, strain...) have frequently been reported. This study investigated just-noticeable differences in the relative amplitudes of the first two harmonics (H1-H2) for speakers of Mandarin and English. Listeners heard pairs of vowels that differed only in the amplitude of the first harmonic and judged whether or not the voice tokens were identical in voice quality. Across voices and listeners, just-noticeable-differences averaged 3.18 dB. This value is small relative to the range of values across voices, indicating that H1-H2 is a perceptually valid acoustic measure of vocal quality. For both groups of listeners, differences in the amplitude of the first harmonic were easier to detect when the source spectral slope was steeply falling so that F0 dominated the spectrum. Mandarin speakers were significantly more sensitive (by about 1 dB) to differences in first harmonic amplitudes than were English speakers. Two explanations for these results are possible: Mandarin speakers may have learned to hear changes in harmonic amplitudes due to changes in voice quality that are correlated with the tones of Mandarin; or Mandarin speakers' experience with tonal contrasts may increase their sensitivity to small differences in the amplitude of F0 (which is also the first harmonic).