Acoustic Measures and Self-reports of Vocal Fatigue by Female Teachers

This study investigated the relation of symptoms of vocal fatigue to acoustic variables reflecting type of voice production and the effects of vocal loading. Seventy-nine female primary school teachers volunteered as subjects. Before and after a working day, (1) a 1-minute text reading sample was recorded at habitual loudness and loudly (as in large classroom), (2) a prolonged phonation on [a:] was recorded at habitual speaking pitch and loudness, and (3) a questionnaire about voice quality, ease, or difficulty of phonation and tiredness of throat was completed. The samples were analyzed for average fundamental frequency (F0), sound pressure level (SPL), and phonation type reflecting alpha ratio (SPL [1-5 kHz]-SPL [50 Hz-1 kHz]). The vowel samples were additionally analyzed for perturbation (jitter and shimmer). After a working day, F0, SPL, and alpha ratio were higher, jitter and shimmer values were lower, and more tiredness of throat was reported. The average levels of the acoustic parameters did not correlate with the symptoms. Increase in jitter and mean F0 in loud reading correlated with tiredness of throat. The results seem to suggest that, at least among experienced vocal professionals, voice production type had little relevance from the point of view of vocal fatigue reported. Differences in the acoustic parameters after a vocally loading working day mainly seem to reflect increased muscle activity as a consequence of vocal loading.     

Discrimination Functions: Can They Be Used to Classify Singing Voices?

Researchers long have searched for invariant acoustic features that can be used to identify singing voice categories or even individual singers. Few researchers have examined how listeners perceive singing voice categories or individual voices. Timbre, the most studied perceptual dimension of the singing voice, is generally believed to vary systematically between singing voice categories but is often assumed to be invariant with an individual singer. To test this assumption, 2 mezzo-sopranos and 2 sopranos were recorded singing the vowel /a/ on the pitches A3, C4, G4, B4, F5, and A5. Trials of three stimuli were constructed. Two of the three stimuli in each trial were produced by the same singer at two different pitches (X₁ and X₂), while the third stimulus was produced by a different singer (Y). Three X₁X₂ conditions were created: (1) G4, B4; (2) C4, F5; and (3) A3, A5. For each singer and each condition, Y was varied across the three remaining singers and across all six pitches. Experienced and inexperienced listeners were asked to identify which stimulus was produced by the “odd” person. The ability to correctly choose the odd person varied greatly depending on pitch factors, suggesting that the traditional concept of an invariant timbre associated with a singer is inaccurate and that vocal timbre must be conceptualized in terms of transformations in perceived quality that occur across an individual singer's range and/or registers.     

Relationship between changes in voice pitch and loudness

Changes in mean fundamental frequency accompanying changes in loudness of phonation are analyzed in 9 professional singers, 9 nonsingers, and 10 male and 10 female patients suffering from vocal functional dysfunction. The subjects read discursive texts with noise in earphones, and some also at voluntarily varied vocal loudness. The healthy subjects phonated as softly and as loudly as possible at various fundamental frequencies throughout their pitch ranges, and the resulting mean phonetograms are compared. Mean pitch was found to increase by about half-semitones per decibel sound level. Grossly, the subject groups gave similar results, although the singers changed voice pitch more than the nonsingers. The voice pitch changes may be explained as passive results of changes of subglottal pressure required for the sound level variation.     

Singing power ratio: Quantitative evaluation of singing voice quality

This paper presents a parameter for objectively evaluating singing voice quality. Power spectrum of vowel sound / a / was analyzed by Fast Fourier Transform. The greatest harmonics peak between 2 and 4 kHz and the greatest harmonics peak between 0 and 2 kHz were identified. Power ratio of these peaks, termed singing power ratio (SPR), was calculated in 37 singers and 20 nonsingers. SPR of sung / a / in singers was significantly greater than in nonsingers. In singers, SPR of sung / a / was significantly greater than that of spoken / a /. By digital signal processing, power spectrum of sung / a / was varied, and the processed sounds were perceptually analyzed. SPR had a significant relationship with perceptual scores of “ringing” quality. SPR provides an important quantitative measurement for evaluating singing voice quality for all voice types, including soprano.     

Effects of vocal training on the acoustic parameters of the singing voice

Vocal training (VT) has, in part, been associated with the distinctions in the physiological, acoustic, and perceptual parameters found in singers' voices versus the voices of nonsingers. This study provides information on the changes in the singing voice as a function of VT over time. Fourteen college voice majors (12 females and 2 males; age range, 17–20 years) were recorded while singing, once a semester, for four consecutive semesters. Acoustic measures included fundamental frequency (F₀) and sound pressure level (SPL) of the 10% and 90% levels of the maximum phonational frequency range (MPFR), vibrato pulses per second, vibrato amplitude variation, and the presence of the singer's formant. Results indicated that VT had a significant effect on the MPFR. F₀ and SPL of the 90% level of the MPFR and the 90–10% range increased significantly as VT progressed. However, no vibrato or singers' formant differences were detected as a function of training. This longitudinal study not only validates previous cross-sectional research, ie, that VT has a significant effect on the singing voice, but also it demonstrates that these effects can be acoustically detected by the fourth semester of college vocal training.     

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.     

Acoustic and Perceptual Analyses of Brazilian Male Actors' and Nonactors' Voices: Long-term Average Spectrum and the “Actor's Formant”

SUMMARY: This study investigates the possible differences between actors' and nonactors' vocal projection strategies using acoustic and perceptual analyses. A total of 11 male actors and 10 male nonactors volunteered as subjects, reading an extended text sample in habitual, moderate, and loud levels. The samples were analyzed for sound pressure level (SPL), alpha ratio (difference between the average SPL of the 1-5kHz region and the average SPL of the 50Hz-1kHz region), fundamental frequency (F0), and long-term average spectrum (LTAS). Through LTAS, the mean frequency of the first formant (F1) range, the mean frequency of the "actor's formant," the level differences between the F1 frequency region and the F0 region (L1-L0), and the level differences between the strongest peak at 0-1kHz and that at 3-4kHz were measured. Eight voice specialists evaluated perceptually the degree of projection, loudness, and tension in the samples. The actors had a greater alpha ratio, stronger level of the "actor's formant" range, and a higher degree of perceived projection and loudness in all loudness levels. SPL, however, did not differ significantly between the actors and nonactors, and no differences were found in the mean formant frequencies ranges. The alpha ratio and the relative level of the "actor's formant" range seemed to be related to the degree of perceived loudness. From the physiological point of view, a more favorable glottal setting, providing a higher glottal closing speed, may be characteristic of these actors' projected voices. So, the projected voices, in this group of actors, were more related to the glottic source than to the resonance of the vocal tract.     

Dissimilarity and the Classification of Male Singing Voices

Traditionally, timbre has been defined as that perceptual attribute that differentiates two sounds when pitch and loudness are equal, and thus is a measure of dissimilarity. By such a definition, each voice possesses a set of timbres, and the ability to identify any voice or voice category across different pitch-loudness-vowel combinations must be due to an ability to "link" these timbres by abstracting the "timbre transformation," the manner in which timbre subtly changes across pitch and loudness for a specific voice or voice category. Using stimuli produced across the singing range by singers from different voice categories, this study sought to examine how timbre and pitch interact in the perception of dissimilarity in male singing voices. This study also investigated whether or not listener experience affects the perception of timbre as a function of pitch. The resulting multidimensional scaling (MDS) representations showed that for all stimuli and listeners, dimension 1 correlated with pitch, while dimension 2 correlated with spectral centroid and separated vocal stimuli into the categories baritone and tenor. Dimension 3 appeared highly idiosyncratic depending on the nature of the stimuli and on the experience of the listener. Inexperienced listeners appeared to rely more heavily on pitch in making dissimilarity judgments than did experienced listeners. The resulting MDS representations of dissimilarity across pitch provide a glimpse of the timbre transformation of voice categories across pitch.     

The ChatterVox™ Portable Voice Amplifier: A Means to Vibration Dose Reduction?

By speaking loudly for extended periods, teachers are vulnerable to laryngeal and voice changes associated with vocal fold “vibration overdose.” Voice clinicians frequently recommend voice amplification ostensibly designed to reduce vibration dose and improve voice. However, there are few data regarding the degree of vocal loudness attenuation achieved by specific amplification devices. The purpose of this investigation was to examine the effectiveness of the ChatterVox™ Portable Voice Amplification System (Siemens Hearing Instruments) for reducing the sound pressure level (SPL) of a speaker's voice during a simulated classroom lecture. Ten participants were instructed to continuously read one of two phonetically balanced passages while amplified and unamplified. Voice intensity measurements were obtained at three inches from the mouth (i.e., mouth level) and at the back of a classroom in both amplified and unamplified conditions. When amplified with the ChatterVox™, speakers experienced an average decrease in vocal intensity at mouth-level of 6.03 dB SPL (p < 0.002). Furthermore, an average increase of 2.55 dB SPL (p < 0.038) at the back of the classroom was observed. Collectively, these results indicate that the ChatterVox™ amplification device reduced the speaker's vocal intensity level at the microphone, while it augmented the voice heard at the back of the classroom. By inference, this degree of vocal attenuation at mouth level should contribute to a desirable reduction in vibration dose, thus lowering the risk of vibration overdose.     

Average speaking fundamental frequency in soprano singers with and without symptoms of vocal attrition

Nineteen trained soprano singers aged 18–30 years vocalized tasks designed to assess average speaking fundamental frequency (SFF) during spontaneous speaking and reading. Vocal range and perceptual characteristics while singing with low intensity and high frequency were also assessed, and subjects completed a survey of vocal habits/symptoms. Recorded signals were digitized prior to being analyzed for SFF using the Kay Computerized Speech Lab program. Subjects were assigned to a normal voice or impaired voice group based on ratings of perceptual tasks and survey results. Data analysis showed group differences in mean SFF, no differences in vocal range, higher mean SFF values for reading than speaking, and 58% ability to perceive speaking in low pitch. The role of speaking in too low pitch as causal for vocal symptoms and need for voice classification differentiation in vocal performance studies are discussed.     

The abduction quotient related to vocal quality

The abduction quotient, a measure of effective glottal width, was obtained for electroglottographic recordings from a professional operatic baritone singer. The subject produced repeated tokens of the voice qualities breathy, normal, and pressed (or constricted) in both a speech and a singing manner. In the singing manner, the subject produced the three vocal qualities at three pitch levels and three loudness levels. The abduction quotient decreased from breathy to pressed voice, suggesting that the measure corresponds to effective glottal width. The measure was found to be consistently low during all conditions of singing, suggesting that the subject produced all singing tokens with relatively strong laryngeal adduction at the vocal process level. Although the results of this study support the validity and usefulness of the abduction quotient, further verification is needed.     

Effects of Professional Singing Education on Vocal Vibrato—A Longitudinal Study

Vocal vibrato is regarded as one of the essential characteristics of voice quality in classical singing. Professional singers seem to develop vibrato automatically, without actively striving to acquire it. In this longitudinal investigation, the vocal vibrato of 22 singing students was examined at the beginning of and after 3 years of professional singing education. Subjects sang an ascending-descending triad pattern in slow tempo on vowel [a:] at a comfortable pitch level twice at soft (piano) and twice at medium (mezzoforte) loudness. The top note of the triad pattern was sustained for approximately 5s. The mean and the standard deviation (SD) of the vibrato rate were measured for this note. Results revealed that after 3 years of training, voices with vibrato slower than 5.2 Hz were found to have a faster vibrato, and voices with vibrato faster than 5.8 Hz were found to have a slower vibrato. Standard deviation of vibrato rate was higher in soft than in medium loudness, particularly before the education. Also high values of SD of vibrato rate, exceeding 0.65 Hz, had decreased after the education. These findings confirm that vibrato characteristics can be affected by singing education.     

Laryngeal and pharyngeal behavior in countertenor and baritone singing—A videofiberscopic study

Changes in vocal tract configuration during singing were studied in four semiprofessional countertenors and one professional bass-baritone, by means of fiberoptic laryngoscopy. All of the countertenors showed a marked narrowing of the lower pharynx with increasing pitch when they used their countertenor voice (CT voice) but only a slight narrowing when using their baritone voice (B voice). The bass-baritone's pharynx remained unchanged with increasing pitch. Increasing loudness gave a widening of the pharynx in three of the four countertenors' CT voices, whereas no change was observed for the countertenors' B voices or for the bass-baritone voice. Vocal fold length seemed to decrease in one countertenor's B voice and in the bass-baritone with increasing loudness. Thus, the countertenors in this study exhibit several characteristic patterns of vocal tract gestures in countertenor voice that differ from both their own baritone voices and from the bass-baritone.     

Pitch Matching Accuracy of Trained Singers, Untrained Subjects with Talented Singing Voices, and Untrained Subjects with Nontalented Singing Voices in Conditions of Varying Feedback

At a physiological level, the act of singing involves control and coordination of several systems involved in the production of sound, including respiration, phonation, resonance, and afferent systems used to monitor production. The ability to produce a melodious singing voice (eg, in tune with accurate pitch) is dependent on control over these motor and sensory systems. To test this position, trained singers and untrained subjects with and without expressed singing talent were asked to match pitches of target pure tones. The ability to match pitch reflected the ability to accurately integrate sensory perception with motor planning and execution. Pitch-matching accuracy was measured at the onset of phonation (prephonatory set) before external feedback could be utilized to adjust the voiced source, during phonation when external auditory feedback could be utilized, and during phonation when external auditory feedback was masked. Results revealed trained singers and untrained subjects with singing talent were no different in their pitch-matching abilities when measured before or after external feedback could be utilized. The untrained subjects with singing talent were also significantly more accurate than the trained singers when external auditory feedback was masked. Both groups were significantly more accurate than the untrained subjects without singing talent.     

Suppression of slag foaming by a sound wave

The aim of this work was to study the effects of sound frequency, sound intensity and viscosity of slag on the slag foaming rate and the steady-state foam height. Experiments were carried out using two slags (BaO–B₂O₃) melted at a temperature of 1223 or 1273 K, as well as water–glycerin solutions at room temperature. Low frequency sound waves (<1.3 kHz) are found to be more effective in the slag foaming suppression than high frequency waves (1.3–12 kHz). The steady-state foam height decreases abruptly when the sound pressure reaches a threshold value that depends on sound frequency and liquid viscosity. The results can be explained in terms of enhancing the rates of liquid drainage and film rupture induced by sound.     

The sound level of the singer's formant in professional singing

The relative sound level of the "singer's formant," measured in a 1/3-oct band with a center frequency of 2.5 kHz for males and of 3.16 kHz for females, has been investigated for 14 professional singers, nine different modes of singing, nine different vowels, variations in overall sound-pressure level, and fundamental frequencies ranging from 98 up to 880 Hz. Variation in the sound level of the singer's formant due to differences among male singers was small (4 dB), the factors vowels (16 dB) and fundamental frequency (9-14 dB) had an intermediate effect, while the largest variation was found for differences among female singers (24 dB), between modes of singing (vocal effort) (23 dB), and in overall sound-pressure level (more than 30 dB). In spite of this great potential variability, for each mode of singing the sound level of the singer's formant was remarkably constant up to F0 = 392 Hz, due to adaptation of vocal effort. This may be explained as the result of the perceptual demand of a constant voice quality. The definition of the singer's formant is discussed.     

Neck and Shoulder Muscle Activity and Thorax Movement in Singing and Speaking Tasks with Variation in Vocal Loudness and Pitch

The aim of this study was to examine respiratory phasing and loading levels of sternocleidomastoideus (STM), scalenus (SC), and upper trapezius (TR) muscles in vocalization tasks with variation in vocal loudness and pitch. Eight advanced singing students, aged 22 to 28 years, participated. Surface electromyographic (EMG) activity was recorded from STM, SC, and TR. Thorax movement was detected by two strain gauge sensors placed around the upper (upper TX) and lower (lower TX) thorax. A glissando and simplified singing and speaking tasks were performed. Sustained vowels /a:-i-ae-o:/ were sung in a glissando from lowest to highest pitch (mixed voice/falsetto) back to lowest pitch and in short singing sequences at comfortable, low, and high pitches. The same vowels were spoken softly and loudly for about the same length. The subjects inhaled between the vowels. It was concluded that the inspiratory phased STM and SC muscles produced a counterforce to compression of upper TX at high pitches in glissando. STM and SC were activated to higher levels during phonation than in inhalation. As breathing demands were reduced, STM and SC activity was lowered and the respiratory phasing of peak amplitude changed to inhalation. TR contributed to exhalation in demanding singing with long breathing cycles, but it was less active in singing tasks with short breathing cycles and was essentially inactive in simplified speaking tasks.     

Electroglottographic wavegrams: a technique for visualizing vocal fold dynamics noninvasively

A method for analyzing and displaying electroglottographic (EGG) signals (and their first derivative, DEGG) is introduced: the electroglottographic wavegram ("wavegram" hereafter). To construct a wavegram, the time-varying fundamental frequency is measured and consecutive individual glottal cycles are identified. Each cycle is locally normalized in duration and amplitude, the signal values are encoded by color intensity and the cycles are concatenated to display the entire voice sample in a single image, similar as in sound spectrography. The wavegram provides an intuitive means for quickly assessing vocal fold contact phenomena and their variation over time. Variations in vocal fold contact appear here as a sequence of events rather than single phenomena, taking place over a certain period of time, and changing with pitch, loudness and register. Multiple DEGG peaks are revealed in wavegrams to behave systematically, indicating subtle changes of vocal fold oscillatory regime. As such, EGG wavegrams promise to reveal more information on vocal fold contacting and de-contacting events than previous methods.     

Vocal responses to unanticipated perturbations in voice loudness feedback: an automatic mechanism for stabilizing voice amplitude

The present study tested whether subjects respond to unanticipated short perturbations in voice loudness feedback with compensatory responses in voice amplitude. The role of stimulus magnitude (+/- 1,3 vs 6 dB SPL), stimulus direction (up vs down), and the ongoing voice amplitude level (normal vs soft) were compared across compensations. Subjects responded to perturbations in voice loudness feedback with a compensatory change in voice amplitude 76% of the time. Mean latency of amplitude compensation was 157 ms. Mean response magnitudes were smallest for 1-dB stimulus perturbations (0.75 dB) and greatest for 6-dB conditions (0.98 dB). However, expressed as gain, responses for 1-dB perturbations were largest and almost approached 1.0. Response magnitudes were larger for the soft voice amplitude condition compared to the normal voice amplitude condition. A mathematical model of the audio-vocal system captured the main features of the compensations. Previous research has demonstrated that subjects can respond to an unanticipated perturbation in voice pitch feedback with an automatic compensatory response in voice fundamental frequency. Data from the present study suggest that voice loudness feedback can be used in a similar manner to monitor and stabilize voice amplitude around a desired loudness level.