Biomedical subjects

I R Titze

Publications and source records attributed to I R Titze.

At least 73 records · Page 4Linked to original sources

PubMed1994

Acoustics of the tenor high voice.

The spectra of six tenors were analyzed at high pitches, F4 to B4. Because of the wide separation between harmonics, formant frequencies could not be extracted in the traditional way. Rather, an analysis-by-synthesis technique was used to match the spectra of a model to the measured spectra, using parameter optimization. Results suggest that tenors maintain their first formant frequencies well above the fundamental for all vowels except [u]. The purpose of this seems to be to distribute the acoustic energy between harmonics 2, 3, and 4 rather than to boost the fundamental. Tuning the first formant to the fundamental is a technique used effectively by sopranos but seems to be deliberately avoided by tenors in order to preserve a male quality.

Humans↗

PubMed1994

Interpretation of biomechanical simulations of normal and chaotic vocal fold oscillations with empirical eigenfunctions.

Empirical orthogonal eigenfunctions are extracted from biomechanical simulations of normal and chaotic vocal fold oscillations. For normal phonation, two dominant empirical eigenfunctions capture the vibration patterns of the folds and exhibit a 1:1 entrainment. The eigenfunctions show some correspondence to theoretical low-order normal modes of a simplified, three-dimensional elastic continuum, and to the normal modes of a linearized two-mass model. The eigenfunctions also facilitate a physical interpretation of energy transfer mechanisms in vocal fold dynamics. Subharmonic regimes and chaotic oscillations are observed during simulations of a lax cover, in which case at least three empirical eigenfunctions are necessary to capture the resulting vocal fold oscillations. These chaotic oscillations might be understood in terms of a desynchronization of a few of the low-order modes, and may be related to mechanisms of creaky voice or vocal fry. Furthermore, some of the empirical eigenfunctions captured during complex oscillations correspond to higher-order normal modes described in earlier theoretical work. The empirical eigenfunctions may also be useful in the design of lower-order models (valid over the range for which the empirical eigenfunctions remain more or less constant), and may help facilitate bifurcation analyses of the biomechanical simulation.

Biomechanical Phenomena↗

PubMed1994

Fundamental frequency and amplitude perturbation in reconstructed canine vocal folds.

A submucosal fat autograft was implanted within the cover of injured vocal folds of 5 dogs. The implant occurred 6 weeks after unilateral mucosal excision had been performed. Three months postoperatively the larynges of these animals were excised and their phonation was compared to that of normal dog larynges and to other larynges with mucosal excision (but without fat grafting). Radiated acoustic pressure from the artificially driven larynges was recorded and digitized at 20 kHz with 16-bit resolution. Amplitude and fundamental frequency perturbations were extracted from a segment of phonation to assess the stability of the acoustic signals from the 3 groups. It was found that fat augmentation after mucosal excision reduced amplitude and frequency perturbation measures. There was no significant difference between fat-augmented and normal vocal folds. The acoustic measures were also positively correlated with phonation threshold and phonation efficiency measures reported earlier. The results suggest that submucosal fat autograft implantation within an injured vocal fold cover can restore not only the "ease" of phonation, but also the stability of phonation, which is a component of vocal quality.

Adipose Tissue↗

PubMed1994

Effect of subglottic pressure on fundamental frequency of the canine larynx with active muscle tensions.

The relation between subglottic pressure and the fundamental frequency of vocal fold vibration was studied by means of evoked phonation in an in vivo canine model. The evoked-phonation model involved electrical stimulation of the midbrain that resulted in consistent responses by respiratory and laryngeal musculature, accompanied by phonation. The dynamic stiffness properties of the vocal folds, especially the "cover," were investigated by delivering various amounts of air pressure to the larynx from an opening in the trachea. The fundamental frequency of vocal fold vibration increased linearly with subglottic pressure. The slopes ranged from 22.4 to 118.7 Hz per kilopascal in 7 animals. The results indicated that the dependence of fundamental frequency on subglottic pressure is a passive mechanical phenomenon.

Animals↗

PubMed1993

Comparison of Fo extraction methods for high-precision voice perturbation measurements.

Voice perturbation measures, such as jitter and shimmer, depend on accurate extraction of fundamental frequency (Fo) and amplitude of various waveform types. The extraction method directly affects the accuracy of the measures, particularly if several waveform types (with or without formant structure) are under consideration and if noise and modulation are present in the signal. For frequency perturbation, high precision is defined here as the ability to extract Fo to +/- 0.01% under conditions of noise and modulation. Three Fo-extraction methods and their software implementations are discussed and compared. The methods are cycle-to-cycle waveform matching, zero-crossing and peak-picking. Interpolation between samples is added to make the extractions more accurate and reliable. The sensitivity of the methods to different parameters such as sampling frequency, mean Fo, signal-to-noise ratio, frequency modulation, and amplitude modulation are explored.

Electronic Data Processing↗

PubMed1993

Effect of microphone type and placement on voice perturbation measurements.

This study was conducted to explore the effects of microphone type (dynamic vs. condenser) and pattern (omnidirectional vs. cardioid) on the extraction of voice perturbation measures for sustained phonation. Also of interest were the effects of distance and angle between the source and the microphone. Four professional-grade and two consumer-grade microphones were selected for analysis. Synthesized phonation with different amplitude and frequency modulations at fundamental frequencies of 100 Hz and 300 Hz were presented over a loudspeaker. Human phonation was also included to test the validity of loudspeaker presentations. Three microphone distances (4 cm, 30 cm, 1 m) and three angles (0 degree, 45 degrees, 90 degrees) were used for microphone placement. Among the professional grade microphones, the cardioid condenser type had the smallest effect on perturbation measures. In general, condenser types gave better results than dynamic types. Microphones with an unbalanced output did not perform as well as those with balanced outputs. Microphone sensitivity and distance had the largest effect on perturbation measures, making it difficult to resolve normal vocal jitter at anything but a few centimeters from the mouth. Angle had little effect for short distances, but a greater effect for longer distances. These conclusions are preliminary because the sampling of microphones, distances, and signal types was very coarse. The study serves only to chart the course for future work.

Amplifiers, Electronic↗

PubMed1993

Measurement of mucosal wave propagation and vertical phase difference in vocal fold vibration.

Examination of the surface wave properties of the vocal fold mucosa is becoming an important part of assessment of vocal function. A key wave property is propagation velocity, which determines the phase delay between the upper and lower margins of the vocal folds. Excised canine larynges were used to measure this phase delay, and therewith propagation velocity. The motion of two flesh points was tracked stroboscopically. Differential displacements between the flesh points were matched to displacements of a model. A least-squared fit of the data to the model provided the numeric values of propagation velocity, which varied from 0.5 m/s to about 2.0 m/s, depending on fundamental frequency. The corresponding phase delay along the medial surface of the vocal folds varied from about 60 degrees/mm to 30 degrees/mm.

Animals↗

PubMed1993

A methodological study of hemilaryngeal phonation.

An excised hemilarynx setup was developed. The phonatory characteristics of nine excised canine larynges were examined. The left vocal fold of each larynx was then removed and substituted with a vertical plexiglass plate. The larynges were phonated again. Recordings were made of phonation threshold pressure, sound pressure level, average glottal flow, fundamental frequency, and amplitude of vocal fold vibration as observed with a video stroboscope. Measurements were made over a range of subglottal pressures. For the hemilarynx, simultaneous recordings of intraglottal pressure and vocal fold contact area were also made. It was found that amplitude and frequency of vocal fold vibration of the hemilarynx, as well as rates of change of amplitude and frequency as a function of subglottal pressure, were similar to those of the full larynx. Also similar were phonation threshold pressures and ranges of subglottal pressure over which the larynges phonated. The average airflow of the hemilarynx was approximately half that of the full larynx, and the sound pressure level, under similar conditions, was one fourth (about 6 dB less) in the hemilarynx.

Animals↗

PubMed1993

Current topics in voice production mechanisms.

A brief overview of current research in voice production mechanisms is given. The self-oscillatory behavior of the vocal folds is clarified, along with the identification of preferred tissue modes. Fundamental frequency control is reviewed as a coordinated activity between cricothyroid and thyroarytenoid muscles and lung pressure. Lung pressure is shown to be the primary regulator of vocal intensity. For eventual application to the study of voice disorders, a method of measurement of contact stress on a hemilarynx preparation is described.

Humans↗

PubMed1993

Fundamental frequency stability in functional dysphonia.

Functional dysphonia is a term applied to voice disorders for which there is an absence of apparent structural change in the larynx. The aim of this work was to investigate how functional dysphonia may differ acoustically from other types of dysphonia. Fundamental frequency profiles for steady vowels were generated using a software program called GLIMPES (Glottal Imaging by Processing External Signals). The fundamental frequency variations were found to be unimodal in normal individuals. In contrast, the variations for dysphonic patients were sometimes bi-modal or multi-modal due to the presence of subharmonics or low-frequency modulations. The appearance of these patterns was generally related to the severity of the dysphonia rather than to its etiology.

Adolescent↗

PubMed1992

Acoustic interpretation of the voice range profile (phonetogram).

The voice range profile (VRP) is a display of vocal intensity range versus fundamental frequency (F0). Past measurements have shown that the intensity range is reduced at the extremes of the F0 range, that there is a gradual upward tilt of the high- and low-intensity boundaries with increasing F0, and that a ripple exists at the boundaries. The intensity ripple, which results from tuning of source harmonics to the formants, is more noticeable at the upper boundary than the lower boundary because higher harmonics are not energized as effectively near phonation threshold as at maximum lung pressure. The gradual tilt of the intensity boundaries results from more effective transmission and radiation of acoustic energy at higher fundamental frequencies. This depends on the spectral distribution of the source power, however, At low F0, a smaller spectral slope (more harmonic energy) produces greater intensity. At high F0, on the other hand, a shift of energy toward the fundamental results in greater intensity. This dependence of intensity on spectral distribution of source power seems to explain the reduced intensity range at higher F0. An unrelated problem of reduced intensity range at low F0 stems from the inherent difficulty of keeping F0 from rising when subglottal pressure is increased.

Female↗

PubMed1992

Phonation threshold pressure: a missing link in glottal aerodynamics.

Phonation threshold pressure has previously been defined as the minimum lung pressure required to initiate phonation. By modeling the dependence of this pressure on fundamental frequency, it is shown that relatively simple aerodynamic relations for time-varying flow in the glottis are obtained. Lung pressure and peak glottal flow are nearly linearly related, but not proportional. For this reason, traditional power law relations between vocal power and lung pressure may not hold. Glottal impendance for time-varying flow should be defined differentially rather than as a simple ratio between lung pressure and peak flow. It is shown that the peak flow, the peak flow derivative, the open quotient, and the speed quotient of inverse-filtered glottal flow waveforms all depend explicitly on phonation threshold pressure. Data from singers are compared with those from nonsingers. The primary difference is that singers obtain two to three times greater peak flow for a given lung pressure, suggesting that they adjust their glottal or vocal tract impedance for optimal flow transfer between the source and the resonantor.

Female↗

PubMed1992

Vocal intensity in speakers and singers.

Vocal intensity is studied as a function of fundamental frequency and lung pressure. A combination of analytical and empirical models is used to predict sound pressure levels from glottal waveforms of five professional tenors and twenty five normal control subjects. The glottal waveforms were obtained by inverse filtering the mouth flow. Empirical models describe features of the glottal flow waveform (peak flow, peak flow derivative, open quotient, and speed quotient) in terms of lung pressure and phonation threshold pressure, a key variable that incorporates the Fo dependence of many of the features of the glottal flow. The analytical model describes the contributions to sound pressure levels SPL by the vocal tract. Results show that SPL increases with Fo at a rate of 8-9 dB/octave provided that lung pressure is raised proportional to phonation threshold pressure. The SPL also increases at a rate of 8-9 dB per doubling of excess pressure over threshold, a new quantity that assumes considerable importance in vocal intensity calculations. For the same excess pressure over threshold, the professional tenors produced 10-12 dB greater intensity than the male nonsingers, primarily because their peak airflow was much higher for the same pressure. A simple set of rules is devised for predicting SPL from source waveforms.

Glottis↗

PubMed1991

A model for neurologic sources of aperiodicity in vocal fold vibration.

The time course of a force twitch in the thyroarytenoid muscle is modeled, and trains of twitches are summed to simulate force tetani. By incorporating means and standard deviations of motoneuron firing rates, and by applying random phase relationships between simulated motor units, a quantitative model of the ripple of vocal fold tension is obtained. From this ripple, perturbations in fundamental frequency are calculated as a function of the number of motor units in the muscle, the mean and standard deviation of the firing rate of dominant motoneurons, and the variability in the size (twitch amplitude) of the motor units. Predicted perturbations range between 0.2% and 1.2%, depending on the choice of parameters. Perturbation decreases with the number of motor units and with increased mean firing rate, but increases with the variability in motor unit size and with variability in the firing rate. Techniques are discussed by which neurologic jitter might be isolated from other sources of irregularity in vocal fold vibration.

Action Potentials↗

PubMed1991

Observation of perturbations in a lumped-element model of the vocal folds with application to some pathological cases.

In this paper a mass-spring model is developed that is a hybrid of the two-mass and the longitudinal string models, proposed by Ishizaka and Flanagan [Bell Sys. Tech. J. 51, 1233-1268 (1972)] and Titze [Phonetica 28, 129-170 (1973)], respectively. The model is used to simulate the vibratory motion of both the normal and asymmetric vocal folds. Mouth-output pressure, lateral tissue displacement, phase plots, and energy diagrams are presented to demonstrate the interaction between vocal fold tissue and the aerodynamic flow between the folds. The results of the study suggest that this interaction is necessary for sustained large amplitude oscillation because the flow supplies the energy lost by the tissue damping. Tissue mass and stiffness were varied locally or uniformly. Decreased stress in the longitudinal string tension produced subharmonic and chaotic vibrations in the displacement, velocity and acceleration phase diagrams. Similar vibratory characteristics also appeared in pathological speech data analyzed using time domain jitter and shimmer measures and a harmonics-to-noise ratio metric. The subharmonics create an effect that has been perceptually described as diplophonia.

Computer Simulation↗

PubMed1991

Elastic models of vocal fold tissues.

Elastic properties of canine vocal fold tissue (muscle and mucosa) were obtained through a series of experiments conducted in vitro and were modeled mathematically. The elastic properties play a significant role in quantitative analysis of vocal fold vibrations and theory of pitch control. Samples of vocalis muscle and mucosa were dissected and prepared from dog larynges a few minutes premortem and kept in a Krebs solution at a temperature of 37 +/- 1 degrees C and a pH of 7.4 +/- 0.05. Samples of muscle tissue and mucosa were stretched and released in a slow, sinusoidal fashion. Force and displacement of the samples were measured with a dual-servo system (ergometer). After digitization, stress-strain data for samples of muscle tissue and cover tissue were averaged. The stress-strain data were then fitted numerically by polynomial and exponential models.

Animals↗

PubMed1991

Tetanic response of the cricothyroid muscle.

Tetanic response of canine cricothyroid muscle tissue was investigated through a series of experiments conducted in vitro. Two separate portions of the cricothyroid muscle, namely the pars recta and pars oblique, were studied. Samples of the muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs-Ringer solution at a temperature of 37 degrees +/- 1 degrees C and a pH of 7.4 +/- 0.05. Tetanic contraction of the muscle samples was obtained by field stimulation to the muscle through a pair of parallel-plate platinum electrodes and with a train of square pulses of 0.1-millisecond duration and 85-V amplitude. Isometric force responses of the pars recta and pars oblique muscles were obtained electronically with a dual servo system (ergometer). The effect of tissue elongation on the active and passive responses was quantified by stimulation of the sample during cyclic elongation. Both active and passive responses as a function of elongation were obtained on the same sample.

Animals↗

PubMed1990

Acoustic analysis of voice in amyotrophic lateral sclerosis: a longitudinal case study.

Acoustic measures of phonatory instability (coefficient of variation for amplitude, coefficient of variation for frequency, shimmer, jitter, and harmonics-to-noise ratio), phonatory limits (maximum fundamental frequency range and maximum duration of vowel phonation), and the nasal-oral amplitude ratio were measured five times throughout a 6-month period from the phonation of a 69-year-old male patient with amyotrophic lateral sclerosis (ALS), an age- and sex-matched control subject, and on one occasion from a 16-subject control group matched to the patient in age and sex. The patient was free of vocal symptoms at the initiation of the study. When compared to the other recording sessions, the final recording of the ALS patient was characterized by increased coefficient of variation for amplitude, increased coefficient of variation for frequency, increased shimmer, increased jitter, reduced harmonics-to-noise ratio, and reduced maximum vowel duration. These acoustic manifestations of increased phonatory instability and reduced phonatory limits over time were in contrast to the consistency observed in the phonation of the longitudinal control subject and were outside the range of plus or minus one standard deviation on most acoustic variables when compared to the control group. These findings support the potential use of acoustic analysis in reflecting progression of ALS and suggest the need for further studies to investigate the relationship between acoustic analysis of voice and manifestations of neurological disease.

Aged↗