Rahul Shrivastav

Objective measures of breathy voice quality obtained using an auditory model

While several acoustic measures have been proposed to quantify listener ratings of breathy voice quality, most have failed to give a consistent and high correlation with perceptual ratings of breathiness. One reason for these limitations is that most acoustic measures do not address the nonlinear processes that occur in the peripheral auditory system during the auditory perceptual process. It was hypothesized that modeling such nonlinear events during signal processing may provide objective parameters that better correspond to perceptual ratings of breathy voice quality. Ten listeners rated 27 voice stimuli using a five-point rating scale. Acoustic measures were determined from these stimuli and were selected based on their history of having a moderate to strong correlation to perceptual ratings of breathiness. The stimuli were also analyzed using an auditory model proposed by Moore, Glasberg, and Baer [J. Audio Eng. Soc. 45(4), 224-239 (1997)], and new measures were calculated from the output of this model. These measures included the partial loudness of the signal and the loudness of the aspiration noise. Measures obtained from the output of the auditory model were found to account for a high amount of variance in the perceptual ratings of breathiness.

The use of an auditory model in predicting perceptual ratings of breathy voice quality

Despite much research, the relationship between vocal acoustic signals and perceived voice quality is not well understood. The present study used an auditory model proposed by Moore et al to study how changes in the acoustic spectrum may relate to changes in perceptual ratings of breathiness. Perceptual ratings of breathiness were obtained using a multidimensional scaling (MDS) design. The stimulus distances on the dominant MDS dimension were correlated with several commonly used acoustic measures for voice quality. These distances were also compared with measures obtained from the output of the auditory model. Results show that the partial loudness of the harmonic energy obtained with the aspiration noise acting as a masker was the most important predictor of perceptual ratings of breathiness. Results also demonstrate that measures obtained from the auditory spectrum were better predictors of perceptual ratings of breathiness than were commonly used acoustic spectral measures.

Some difference limens for the perception of breathiness.

Perception of breathy voice quality appears to be cued by changes in the vowel spectrum. These changes are related to alterations in the intensity of aspiration noise and spectral slope of the harmonic energy [Shrivastav and Sapienza, J. Acoust. Soc. Am., 114 (4), 2217-2224 (2003)]. Ten young-adult listeners with normal hearing were tested using an adaptive listening task to determine the smallest change in signal-to-noise ratio that resulted in a change in breathiness. Six vowel continua, three female and three male, were generated using a Klatt synthesizer and served as stimuli. Results showed that listeners needed as much as 20-dB increase in aspiration noise to perceive a change in breathiness against a relatively normal voice. In contrast, listeners needed approximately an 11-dB increase in aspiration noise to discriminate breathiness against a severely breathy voice. The difference limens for breathiness were observed to vary across the six talkers. Voices having aspiration noise that was predominantly in the high frequencies had smaller difference limens. No significant differences for male and female voice were observed.

Noise and tremor in the perception of vocal aging in males.

OBJECTIVE/HYPOTHESIS To specify a set of acoustic cues for vocal aging and to establish their perceptual relevance. STUDY DESIGN Perceptual testing. METHODS To identify the acoustic and perceptual correlates of the aging voice, voice quality [in conjunction with speaking rate and fundamental frequency (F(0))] was systematically manipulated using resynthesis to determine its effect on perceived age. Ten young male voices were resynthesized using two levels of noise (random modulation of F(0) contour) and two levels of tremor (constant modulation of F(0) contour with a low-amplitude wave) under a speaking-rate manipulation (an increase in speaking rate that is common to older male voices). These materials were submitted to 40 naive listeners in an age-estimation task. Two sets of comparison materials were also included for evaluation: unmanipulated samples from a 150 voice database of young, middle-aged, and older voices and disordered voice samples representing natural manifestations of the voice qualities of interest. RESULTS Speaking rate, highest degree of tremor, and highest degree of noise all shifted, in an additive manner, the mean perceived age of the young male voices by a maximum of 12 years on average; individual voices were observed being shifted by a generation. Fundamental frequency manipulations had no significant effect on perceived age. CONCLUSIONS Voice quality (both tremor and noise) and speaking rate are all perceptually relevant cues of age in male voices.

Perceptual Distances of Breathy Voice Quality: A Comparison of Psychophysical Methods

Experiments to study voice quality have typically used rating scales or direct magnitude estimation to obtain listener judgments. Unfortunately, the data obtained using these tasks are context dependent, which makes it difficult to compare perceptual judgments of voice quality across experiments. The present experiment describes a simple matching task to quantify voice quality. The data obtained through this task were compared to perceptual judgments obtained using rating scale and direct magnitude estimation tasks to determine whether the three tasks provide equivalent perceptual distances across stimuli. Ten synthetic vowel continua that varied in terms of their aspiration noise were evaluated for breathiness using each of the three tasks. Linear and nonlinear regressions were used to compare the perceptual distances between stimuli obtained through each technique. Results show that the perceptual distances estimated from matching and direct magnitude estimation task are similar, but both differ from the rating scale task, suggesting that the matching task provides perceptual distances with ratio-level measurement properties. The matching task is advantageous for measurement of vocal quality because it provides reliable measurement with ratio-level scale properties. It allows the use of a fixed reference signal for all comparisons, thus allowing researchers to directly compare findings across different experiments.

Disordered speech assessment using automatic methods based on quantitative measures

Speech quality assessment methods are necessary for evaluating and documenting treatment outcomes of patients suffering from degraded speech due to Parkinsons disease, stroke, or other disease processes. Subjective methods of speech quality assessment are more accurate and more robust than objective methods but are time-consuming and costly. We propose a novel objective measure of speech quality assessment that builds on traditional speech processing techniques such as dynamic time warping (DTW) and the Itakura-Saito (IS) distortion measure. Initial results show that our objective measure correlates well with the more expensive subjective methods.

Combined modality treatment of adductor spasmodic dysphonia.

INTRODUCTION The hallmark characteristic of adductor spasmodic dysphonia (ADSD) is irregular and uncontrollable spasms within the intrinsic laryngeal muscles, resulting in erratic disruption of normal voicing. METHODS Using a random assignment and the inclusion of a behavioral sham to determine the effect of voice therapy after initial botulinum toxin type A (BTX-A) injections for ADSD, this study examined duration of injection benefit, perceived vocal quality of life from the Voice-Related Quality of Life (V-RQOL) scale, acoustic measures of vocal instability, and perceptual ratings of voice quality. Measures of these variables were collected before initial injection; 3, 7, and 12 weeks postinjection; and immediately before reinjection. Thirty-one individuals with ADSD participated in this study. One-third received no further intervention after BTX-A injection, one-third received a standard 5-week course of voice therapy after BTX-A injection, and one-third received a 5-week course of sham voice therapy after BTX-A injection. RESULTS AND CONCLUSIONS Significant effects were observed on perceived quality of life and acoustic variables for all participants, over time. Participants who received voice therapy after BTX-A injection did not experience longer injection effect duration or significantly greater improvements in V-RQOL or acoustic variables than participants in BTX-A only or BTX-A plus sham therapy groups. Additionally, perceptual ratings of voice quality improved for all participants in response to BTX-A injection. For participants in this investigation, undertaking voice therapy did not appear to exert significant beneficial effects on the variables of interest.

Differential sensitivity of cranial and limb motor function to nigrostriatal dopamine depletion.

The present study determined the differential effects of unilateral striatal dopamine depletion on cranial motor versus limb motor function. Forty male Long Evans rats were first trained on a comprehensive motor testing battery that dissociated cranial versus limb motor function and included: cylinder forepaw placement, single pellet reaching, vermicelli pasta handling; sunflower seed opening, pasta biting acoustics, and a licking task. Following baseline testing, animals were randomized to either a 6-hydroxydopamine (6-OHDA) (n=20) or control (n=20) group. Animals in the 6-OHDA group received unilateral intrastriatal 6-OHDA infusions to induce striatal dopamine depletion. Six-weeks following infusion, all animals were re-tested on the same battery of motor tests. Near infrared densitometry was performed on sections taken through the striatum that were immunohistochemically stained for tyrosine hydroxylase (TH). Animals in the 6-OHDA condition showed a mean reduction in TH staining of 88.27%. Although 6-OHDA animals were significantly impaired on all motor tasks, limb motor deficits were more severe than cranial motor impairments. Further, performance on limb motor tasks was correlated with degree of TH depletion while performance on cranial motor impairments showed no significant correlation. These results suggest that limb motor function may be more sensitive to striatal dopaminergic depletion than cranial motor function and is consistent with the clinical observation that therapies targeting the nigrostriatal dopaminergic system in Parkinsons disease are more effective for limb motor symptoms than cranial motor impairments.

Acoustic parameters critical for an appropriate vibrato.

BACKGROUND A plethora of investigations have studied the acoustic characteristics of vibrato such as the rate, extent, onset (time from initiation of phonation until the first peak of vibrato), and periodicity. Despite extensive research, the degree to which various parameters of vibrato contribute to its acceptability remain unclear. PURPOSE The present study sought to determine the psychoacoustical relationship of mean fundamental frequency (f(0)), modulation frequency (f(f0m)), modulation depth (d(f0m)), and intensity to the appropriateness or inappropriateness of vibrato. METHOD Phonation samples of eight voice majors singing at low, middle, and high pitches were obtained. A high fidelity vocoder (STRAIGHT; Kawahara, 1997) was used to resynthesize these vowels with systematic manipulations of f(f0m) and d(f0m) of the f(0) contours resulting in a total of 600 stimuli (8 singers×3 pitches×5 f(f0m) levels×5 d(f0m) levels). Nine listeners (four experts and five students) evaluated these stimuli for appropriateness of vibrato at two different presentation levels (70 and 90 dB sound pressure level). RESULTS Statistical analyses of the perceptual data suggest that appropriateness of vibrato tends to increase with mean f(0) and decrease with d(f0m.) Appropriateness of vibrato is greatest for f(f0m) value of 6 Hz, but decreases both above and below this frequency. CONCLUSION perceived appropriateness of vibrato results from an interaction of mean f(0), f(f0m), and d(f0m) of the vowel waveform.

Disordered speech evaluation using objective quality measures

Speech quality assessment methods are necessary for evaluating and documenting treatment outcomes of patients suffering from degraded speech due to Parkinsons disease, stroke or other disease processes. Subjective methods of speech quality assessment are more accurate and more robust than objective methods but are time-consuming and costly. We propose a novel objective measure of speech quality assessment that builds on traditional speech processing techniques such as dynamic time warping (DTW) and the Itakura-Saito (IS) distortion measure. Initial results show that our objective measure correlates well with the more expensive subjective methods.