Augmented visual-feedback of airflow: Immediate effects on voice-source characteristics of students of singing

Glottal adduction is a crucial aspect in voice education and vocal performance: it has major effects on phonatory airflow and, consequently, on voice timbre. As the voice is a non-visible musical instrument, controlling it could be facilitated by providing real-time visual feedback of phonatory airflow. Here, we test the usefulness of a flow ball (FB) training device, visualizing, in terms of the height of a polystyrene ball placed in a plastic basket, phonatory airflow during phonation. Audio and electroglottographic recordings of five postgraduate, classically trained singer students were made under three subsequent conditions: before, during, and after phonating into the FB. The calibrated audio signal was inverse-filtered, using an electroglottograph signal to guide the manual tuning of the inverse filters. Mean phonatory airflow, peak-to-peak pulse amplitude, and normalized amplitude quotient were extracted from the resulting flow glottograms. After the FB condition, increases of mean flow and peak-to-peak pulse amplitude were observed in four singers. In addition, the singers’ mean normalized amplitude quotient increased significantly. The findings, although exploratory, suggest that reduction of glottal adduction can be observed immediately after FB phonation.

Development of Parameters towards Voice Bifurcations

Pathological vocal folds are known to exhibit multiple oscillation patterns, depending on tissue imbalance, subglottal pressure level, and other factors. This includes mid-phonation changes due to bifurcations in the underlying voice source system. Knowledge of when changes in oscillation patterns occur is helpful in the assessments of voice disorders, and the knowledge could be transformed into useful objective measures. Mid-phonation bifurcations can occur in rapid succession; hence, a fast classification of oscillation pattern is critical to minimize the averaging of data across bifurcations. This paper proposes frequency-ratio based short-term measures, named harmonic disturbance factor (HDF) and biphonic index (BI), towards the detection of the bifurcations. For the evaluation of HDF and BI, a frequency selection algorithm for glottal source signals is devised, and its efficacy is demonstrated with the glottal area waveforms of four cases, representing the wide range of oscillatory behaviors. The HDF and BI exhibit clear transitions when the voice bifurcations are apparent in the spectrograms. The presented proof-of-concept experiment’s outcomes warrant a larger scale study to formalize the parameters of the frequency selection algorithm.

Efficient numerical simulation of the human voice

The process of voice production is a complex process and depends on the correct interaction of the vocal folds and the glottal airstream inducing the primary voice source, which is subsequently modulated by the vocal tract. Due to the restricted access to the glottis, not all aspects of the three-dimensional process can be captured by measurements without influencing the measurement object. Hence, the application of a numerical tool capturing the physical process of phonation can provide an extended database for voice treatment and, therefore, can contribute to an increased effectiveness of voice treatment. However, such numerical models involve complex and demanding procedures to model the material behavior and the mechanical contact of the vocal folds and to realize moving boundaries of the involved physical domains. The present paper proposes a numerical model called simVoice, which circumvents these computational expenses by prescribing the experimentally obtained vocal fold motion within the simulation. Additionally, a hybrid approach for sound computation further enhances the computational efficiency and yields good agreement with acoustic measurements. An analysis of the computational workloads suggests that the key factor for a further increase in efficiency is an optimized flow simulation and source term computation.

Subglottal pressure oscillations in anechoic and resonant conditions and their influence on excised larynx phonations

Excised larynges serve as natural models for studying behavior of the voice source. Acoustic resonances inside the air-supplying tubes below the larynx (i.e., subglottal space), however, interact with the vibratory behavior of the larynges and obscure their inherent vibration properties. Here, we explore a newly designed anechoic subglottal space which allows removing its acoustic resonances. We performed excised larynx experiments using both anechoic and resonant subglottal spaces in order to analyze and compare, for the very first time, the corresponding subglottal pressures, electroglottographic and radiated acoustic waveforms. In contrast to the resonant conditions, the anechoic subglottal pressure waveforms showed negligible oscillations during the vocal fold contact phase, as expected. When inverted, these waveforms closely matched the inverse filtered radiated sound waveforms. Subglottal resonances modified also the radiated sound pressures (Level 1 interactions). Furthermore, they changed the fundamental frequency (fo) of the vocal fold oscillations and offset phonation threshold pressures (Level 2 interactions), even for subglottal resonance frequencies 4–10 times higher than fo. The obtained data offer the basis for better understanding the inherent vibratory properties of the vocal folds, for studying the impact of structure-acoustic interactions on voice, and for validation of computational models of voice production.