Comparisons of jitter, shimmer, and signal-to-noise ratio from directly digitized versus taped voice samples

The purpose of this study was to compare jitter, shimmer, and signal-to-noise ratio (SNR) measures obtained from tape-recorded samples with the same measures made on directly digitized voice samples, with use of the CSpeech acoustic analysis program. Subjects included 30 young women who phonated the vowel /a/ at a comfortable pitch and loudness level. Voice samples were simultaneously recorded and digitized, and the resulting perturbation measures for the two conditions were compared. Results indicated that there were small but statistically significant differences between percent jitter, percent shimmer, and SNR calculated from taped samples compared with the same measures calculated from directly digitized samples. It was concluded that direct digitization for clinical measures of vocal perturbation was most desirable, but that taped samples could be used, if necessary, with some caution.     

Spectral models of additive and modulation noise in speech and phonatory excitation signals

The article presents spectral models of additive and modulation noise in speech. The purpose is to learn about the causes of noise in the spectra of normal and disordered voices and to gauge whether the spectral properties of the perturbations of the phonatory excitation signal can be inferred from the spectral properties of the speech signal. The approach to modeling consists of deducing the Fourier series of the perturbed speech, assuming that the Fourier series of the noise and of the clean monocycle-periodic excitation are known. The models explain published data, take into account the effects of supraglottal tremor, demonstrate the modulation distortion owing to vocal tract filtering, establish conditions under which noise cues of different speech signals may be compared, and predict the impossibility of inferring the spectral properties of the frequency modulating noise from the spectral properties of the frequency modulation noise (e.g., phonatory jitter and frequency tremor). The general conclusion is that only phonatory frequency modulation noise is spectrally relevant. Other types of noise in speech are either epiphenomenal, or their spectral effects are masked by the spectral effects of frequency modulation noise.     

Perception of aperiodicities in synthetically generated voices

The purpose of this study was to investigate univariate relationships between perceived dysphonia and variation in pitch perturbation, amplitude perturbation, and additive noise. A time-domain, pitch-synchronous synthesis technique was used to generate sustained vowels varying in each of the three acoustic dimensions. A panel of trained listeners provided direct magnitude estimates of roughness in the case of the stimuli varying in pitch and amplitude perturbation, and breathiness in the case of the stimuli varying in additive noise. Very strong relationships were found between perceived roughness and either pitch or amplitude perturbation. However, unlike results reported previously for nonspeech stimuli, the subjective quality associated with pitch perturbation was quite different from that associated with amplitude perturbation. Results also showed that perceived roughness was affected not only by the amount of perturbation, but also by the degree of correlation between adjacent pitch or amplitude values. A strong relationship was found between perceived breathiness and signal-to-noise ratio. Contrary to previous findings, there was no interaction between signal-to-noise ratio and the amount of high-frequency energy in the periodic component of the stimulus: Stimuli with similar signal-to-noise ratios received similar ratings, regardless of differences in the spectral slope of the periodic component.     

Transmission of noise coded versus additive signals through a neuronal ensemble

Neuronal populations receive signals through temporally inhomogeneous spike trains which can be approximated by an input consisting of a time dependent mean value (additive signal) and noise with a time dependent intensity (noise coded signal). We compare the linear response of an ensemble of model neurons to these signals. Our analytical solution for the mean activity demonstrates the high efficiency of the transmission of a noise coded signal in a broad frequency band. For both kinds of signal we show that the transmission by the ensemble reveals stochastic resonance as well as a nonmonotonous dependence on the driving frequency.     

Effects of practice with and without knowledge of results on jitter and shimmer levels in normally speaking women

The effects of practice on jitter and shimmer were assessed in two groups of normally speaking women. Subjects in both groups sustained trials of /a/ as steadily as possible during a baseline session, two practice sessions, and a transfer session. Subjects in one group received visual and verbal feedback during the practice sessions. Subjects in the other group received no feedback. Shimmer means remained essentially stable over the four sessions for both groups, and no differences were apparent between the groups. Jitter values were significantly different between sessions for both groups, and between the two groups for the practice sessions. These results are consistent with findings from manual performance and retention tasks. The present findings also support a recently developed neurologic model of jitter.     

Post-processing synchronization and characterization of generated signals by a repetitive Marx generator

In the present paper, a new approach was developed for solving the problem of time synchronization of a set of signals obtained by different measurement techniques without a common trigger. The recorded signals were the result of sparks and bursts generated by a repetitive Marx generator. A thermal imaging camera, a high speed camera and an audio recorder were used to obtain the necessary data for synchronization and characterization. Moreover, a piezoelectric sensor was applied for shock waves characterization during the early stages of bursts. In the first place, different data with evident time shifts were acquired. Then, A set of simple operations such as maximum selection and localization, threshold comparison, Euclidean distance calculation and minimization were employed for signal analysis and pattern matching to ensure a good data synchronization, which allowed a detailed analysis of the phenomenon in the end.     

嗓音源谐波噪声独立分量分离估计方法

以发声生理和病理为基础,针对唇端语音、线性预测反滤波处理后的声门气流体积速度波和颈前体表传导嗓音信号分别采用独立分量分析,分离出谐波与噪声信号,并估计其谐波噪声比。在不同元音、不同发声方式以及不同病变条件下给出了实验结果,并与传统的谐波噪声比计算方法进行综合比较。分别证实了在正常和病变条件下更客观、准确地判断嘶音程度和喉病的适应方法。对发声基础研究、语言声学和喉病检测等领域有重要意义。     

Investigation of a glottal related harmonics-to-noise ratio and spectral tilt as indicators of glottal noise in synthesized and human voice signals

The harmonics-to-noise ratio (HNR) of the voiced speech signal has implicitly been used to infer information regarding the turbulent noise level at the glottis. However, two problems exist for inferring glottal noise attributes from the HNR of the speech wave form: (i) the measure is fundamental frequency (f0) dependent for equal levels of glottal noise, and (ii) any deviation from signal periodicity affects the ratio, not just turbulent noise. An alternative harmonics-to-noise ratio formulation [glottal related HNR (GHNR')] is proposed to overcome the former problem. In GHNR' a mean over the spectral range of interest of the HNRs at specific harmonic/between-harmonic frequencies (expressed in linear scale) is calculated. For the latter issue [(ii)] two spectral tilt measures are shown, using synthesis data, to be sensitive to glottal noise while at the same time being comparatively insensitive to other glottal aperiodicities. The theoretical development predicts that the spectral tilt measures reduce as noise levels increase. A conventional HNR estimator, GHNR' and two spectral tilt measures are applied to a data set of 13 pathological and 12 normal voice samples. One of the tilt measures and GHNR' are shown to provide statistically significant differentiating power over a conventional HNR estimator.     

Correcting the use of ensemble averages in the calculation of harmonics to noise ratios in voice signals (L)

A correcting formula for the estimation of harmonics-to-noise ratios (HNR) based on ensemble-averaging techniques is derived. The original method yields a biased approximation which is more accurate as the number of averaged pulses (N) increases. However, the method treats gradual waveform changes incorrectly as noise, which is worsened for large values of N. The obtained formula allows the use of as few averaged pulses as desired, while allowing the complete removal of the bias from the estimate of HNR.     

Perceptual interaction of the harmonic source and noise in voice

Although the amount of inharmonic energy (noise) present in a human voice is an important determinant of vocal quality, little is known about the perceptual interaction between harmonic and inharmonic aspects of the voice source. This paper reports three experiments investigating this issue. Results indicate that perception of the harmonic slope and of noise levels are both influenced by complex interactions between the spectral shape and relative levels of harmonic and noise energy in the voice source. Just-noticeable differences (JNDs) for the noise-to-harmonics ratio (NHR) varied significantly with the NHR and harmonic spectral slope, but NHR had no effect on JNDs for NHR when harmonic slopes were steepest, and harmonic slope had no effect when NHRs were highest. Perception of changes in the harmonic source slope depended on NHR and on the harmonic source slope: JNDs increased when spectra rolled off steeply, with this effect in turn depending on NHR. Finally, all effects were modulated by the shape of the noise spectrum. It thus appears that, beyond masking, understanding perception of individual parameters requires knowledge of the acoustic context in which they function, consistent with the view that voices are integral patterns that resist decomposition.     

Stochastic resonance in linear system driven by multiplicative noise and additive quadratic noise

In this paper the stochastic resonance (SR) is studied in an overdamped linear system driven by multiplicative noise and additive quadratic noise. The exact expressions are obtained for the first two moments and the correlation function by using linear response and the properties of the dichotomous noise. SR phenomenon exhibits in the linear system. There are three different forms of SR: the bona fide SR, the conventional SR and SR in the broad sense. Moreover, the effect of the asymmetry of the multiplicative noise on the signal-to-noise ratio (SNR) is different from that of the additive noise and the effect of multiplicative noise and additive noise on SNR is different.     

Intensity correlations in the presence of additive background noise

The mean value of the intensity correlation function and intensity spectrum of a bar object are evaluated when a spatialy random intensity is added to the deterministic object. The mean value of both functions depends upon two terms in addition to the usual term involving the deterministic object, one involves the mean and the other involves the covariance of the random background intensity.     

Scaling behavior of a nonlinear oscillator with additive noise,white and colored

We study analytically and numerically the problem of a nonlinear mechanical oscillator with additive noise in the absence of damping. We show that the amplitude, the velocity and the energy of the oscillator grow algebraically with time. For Gaussian white noise, an analytical expression for the probability distribution function of the energy is obtained in the long-time limit. In the case of colored, Ornstein-Uhlenbeck noise, a self-consistent calculation leads to (different) anomalous diffusion exponents. Dimensional analysis yields the qualitative behavior of the prefactors (generalized diffusion constants) as a function of the correlation time. Received 10 October 2002 Published online 6 March 2003 RID="a" ID="a"e-mail: mallick@spht.saclay.cea.fr     

Emergent bistability: Effects of additive and multiplicative noise

Positive feedback and cooperativity in the regulation of gene expression are generally considered to be necessary for obtaining bistable expression states. Recently, a novel mechanism of bistability termed emergent bistability has been proposed which involves only positive feedback and no cooperativity in the regulation. An additional positive feedback loop is effectively generated due to the inhibition of cellular growth by the synthesized proteins. The mechanism, demonstrated for a synthetic circuit, may be prevalent in natural systems also as some recent experimental results appear to suggest. In this paper, we study the effects of additive and multiplicative noise on the dynamics governing emergent bistability. The calculational scheme employed is based on the Langevin and Fokker-Planck formalisms. The steady state probability distributions of protein levels and the mean first passage times are computed for different noise strengths and system parameters. In the region of bistability, the bimodal probability distribution is shown to be a linear combination of a lognormal and a Gaussian distribution. The variances of the individual distributions and the relative weights of the distributions are further calculated for varying noise strengths and system parameters. The experimental relevance of the model results is also pointed out.