Speech Disorder — Vocal Folds Essay: The modeling of normal and pathological voice source and the analysis of healthy and pathological voices has gained increasing interest recently. Vocal Pathologies Most voice-related pathologies are due to irregular masses or the presence of pathologies in the larynx such as vocal fold nodules or vocal fold polyps located on the vocal folds interfering in their normal and regular vibration. This phenomenon causes a decrease in voice quality, that is, usually the first symptom of this type of disorders.
Speech Disorder — Vocal Folds Essay: The modeling of normal and pathological voice source and the analysis of healthy and pathological voices has gained increasing interest recently.
Vocal Pathologies Most voice-related pathologies are due to irregular masses or the presence of pathologies in the larynx such as vocal fold nodules or vocal fold polyps located on the vocal folds interfering in their normal and regular vibration. This phenomenon causes a decrease in voice quality, that is, usually the first symptom of this type of disorders.
In the past, the only way to measure voice quality was by applying perceptual measurements denoting the existence or absence of several voice characteristics . To analyze the speech signal in order to estimate numerous parameters that indicate amplitude and frequency perturbations, the level of air leakage, the degree of turbulence, and so forth.
Voice Quality Analysis Voice production starts with the vibration of the vocal folds, which can be more or less stretched to achieve higher or lower pitch tones. In normal conditions and in spite of this pitch variation ability, phonation is considered stabilized and regular.
The same problem can occur in amplitude. If, for instance, the vocal folds are too stiff, they will need a higher sub glottal pressure to vibrate. The glottal cycle can thus be irregularly disturbed also in amplitude, originating shimmer.
The possible existence of high frequency noise, especially during the closed phase of the glottal cycle, originated by a partial closure of the vocal folds will cause an air leakage through the glottis, providing a turbulence effect.
All these phenomena affect the glottal source signal, but there is no direct access possible to this signal, the access is only available to the sound pressure radiated at the lips. The estimation of the glottal source signal from the voice signal is not a simple task.
Research in this field shows that it is reasonable to approximate the influence of the vocal tract by a linear filter. Using this approximation, the voice signal can be filtered by inverse of this filter to obtain an estimate of the glottal source signal .
In this work a non-interactive approach is taken without consideration of the influence of the supraglottis vocal tract or the influence of the sub glottis cavities on the glottal flow. As a consequence, it is assumed that the source and filter parameters are independent.
Details of the vocal tract and the utterances with respect to different articulators are indicated below. Fundamental frequency is defined as follows. The vocal fundamental frequency is reflective of the biomechanical characteristics of the vocal folds as they interact with sub glottal pressure.
The biomechanical properties are determined by laryngeal structure and applied muscle forces. Adjustment of the latter, in turn, is a function of reflective, affective and learned voluntary behaviors. The small cycle-to-cycle changes in frequency are represented by frequency perturbations or what is called jitter.
The estimation of irregularities in the vibration of the vocal folds is commonly measured by the jitter parameter. Jitter measures the irregularities in a quasi-periodic signal and can account for variations in one or more of its features, like period, amplitude, shape, and so forth .
Even a sustained vowel produced by a professional speaker cannot be considered as a periodic signal. Hence, the jitter of a voiced speech signal is usually taken as a measure of the change in the duration of consecutive glottal cycles.
Jitter the instability of vocal fold vibration represents a reflection of biomechanical and neuromuscular control. Perturbation values can vary in several ways. Variations of pitch perturbation are inversely proportional to the frequency, for example when fundamental frequency increases, jitter decreases.
Variations of pitch perturbation is expected to change in relation to the degree of tension present in the vocal folds, where high tension reflects lower perturbation values and low tension reflects higher perturbation values.
Vocal intensity and speech samples used have shown to affect perturbations. The effects of intensity on jitter values are as follows. The higher jitter ratios were related to low pitch and intensity of sustained vowels. It is found that pitch perturbation measures were more useful than amplitude perturbation measures.Neo-Impressionism is a term applied to an avant-garde art movement that flourished principally in France from to Led by the example of Georges Seurat, artists of the Neo-Impressionist circle renounced the random spontaneity of Impressionism in favor of a measured painting technique grounded in science and the study of optics.
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