Fundamental Frequency Control Research Articles

Bayesian inference of state feedback control parameters for fo perturbation responses in cerebellar ataxia.

Behavioral speech tasks have been widely used to understand the mechanisms of speech motor control in typical speakers as well as in various clinical populations. However, determining which neural functions differ between typical speakers and clinical populations based on behavioral data alone is difficult because multiple mechanisms may lead to the same behavioral differences. For example, individuals with cerebellar ataxia (CA) produce atypically large compensatory responses to pitch perturbations in their auditory feedback, compared to typical speakers, but this pattern could have many explanations. Here, computational modeling techniques were used to address this challenge. Bayesian inference was used to fit a state feedback control (SFC) model of voice fundamental frequency (fo) control to the behavioral pitch perturbation responses of speakers with CA and typical speakers. This fitting process resulted in estimates of posterior likelihood distributions for five model parameters (sensory feedback delays, absolute and relative levels of auditory and somatosensory feedback noise, and controller gain), which were compared between the two groups. Results suggest that the speakers with CA may proportionally weight auditory and somatosensory feedback differently from typical speakers. Specifically, the CA group showed a greater relative sensitivity to auditory feedback than the control group. There were also large group differences in the controller gain parameter, suggesting increased motor output responses to target errors in the CA group. These modeling results generate hypotheses about how CA may affect the speech motor system, which could help guide future empirical investigations in CA. This study also demonstrates the overall proof-of-principle of using this Bayesian inference approach to understand behavioral speech data in terms of interpretable parameters of speech motor control models.

Control of Regenerative CHB Motor Drives at Fundamental Switching Frequency

To handle the high-power regeneration power in coal and mine industry applications, the regenerative version of the cascaded H-bridge (CHB) drives is made possible by replacing the diode-front-end rectifier with a three-phase IGBT-based active-front-end (AFE) rectifier in each power cell. However, the IGBT switching devices introduce extra switching losses to the system that must be properly handled due to the thermal constraints in high power medium voltage drive applications. In this article, a novel fundamental switching frequency control strategy is proposed for the AFEs in the regenerative CHB drive. With the proposed control strategy, the main harmonic contents generated by the AFEs are well-reshaped at a low-order harmonics range which can be further eliminated by the existing front-end phase-shifting transformer. This allows accomplishing the meeting of the IEEE std 519-2014 at the fundamental switching frequency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sw</sub> = 60. Moreover, with the proposed switching pattern, IGBTs can be turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> at zero current and therefore it can reduce switching losses simultaneously. The feasibility of the proposed control strategy is verified by experimental results on a seven-level regenerative CHB drive, which can be extended to regenerative CHB drives with any voltage levels.

Task-Dependent Modulation of Auditory Feedback Control of Vocal Intensity

Auditory feedback control of fundamental frequency (fo) is modulated in a task-dependent manner. When voice pitch auditory feedback perturbations are applied in sentence versus sustained-vowel production, larger and faster vocal fo responses are measured in sentence production. This task-dependency reflects the scaling of auditory targets for pitch for the precision required in each speech task. When the range for the pitch auditory target is scaled down for precision (as in the sentence-production task), a greater degree of mismatch is detected from the feedback perturbation and a larger vocal response is measured. The purpose of this study was to determine whether auditory feedback control of vocal intensity is also modulated in a task-dependent manner similar to the control of vocal pitch. Twenty-five English speakers produced repetitions of a sentence and a sustained vowel while hearing their voice auditory feedback briefly perturbed in loudness (+/- 3 or 6 dB SPL, 200 ms duration). The resulting vocal intensity responses were measured, and response magnitudes were robustly larger in the sentence (mean: 1.96 dB) than vowel production (mean: 0.89 dB). Additionally, response magnitudes increased as a function of perturbation magnitude only in sentence production for downward perturbations but decreased in magnitude by perturbation magnitude for upward perturbations. Peak response latencies were robustly shorter in sentence (mean: 184.94 ms) than in vowel production (mean: 214.92 ms). Overall, these results support the hypothesis that auditory feedback control of pitch and loudness are modulated by task and that both pitch and loudness auditory targets are scaled for the precision required for the speaking task.

Developing a Generalized Multi-Level Inverter with Reduced Number of Power Electronics Components

Reducing the number of components of power electronic converters has been an important research topic over the past few decades. This paper introduces a new structure for a multi-level inverter based on reduced switch basic modules. The proposed basic module requires fewer switches and auxiliary devices. In addition, a lesser number of on-state switches for the synthesis of each voltage level results in less conduction losses, which enhances the converter efficiency. The proposed structure is capable of being implemented in both symmetrical and asymmetrical topologies. This is a merit feature for the proposed topology, which produces high voltage levels with a limited number of elements. The proposed structure is controlled using the fundamental frequency control scheme. The proposed basic module consists of six unidirectional switches and five DC voltage sources, generating five positive voltage levels. The performance of the recommended topology is analyzed from the various circuitry parameters, and a comprehensive comparison carried out with similar recent structures. The presented comparison reveals the advantage of the recommended inverter from different aspects of the circuitry parameters. The suggested structure is simulated using Matlab/Simulink software, and its performance is validated using a laboratory prototype. The results are reported for various steady-state and dynamic conditions.

High Frequency Resonance Suppression Strategy of Three-Phase Four-Wire Split Capacitor Inverter Connected to Parallel Compensation Grid

With the continuous penetration and development of renewable energy power generation, the distributed grid and the microgrid are becoming increasingly important in modern power systems. In distribution networks and the microgrid, the grid impedance is comparatively large and cannot be ignored. Usually, the parallel compensation is used to improve the grid quality. In the grid with parallel compensation, the large phase angle difference between the impedance of the grid-connected inverter and the impedance of the grid at amplitude intersection will result in high frequency resonance (HFR). Because the inverter shows filter characteristics due to limited bandwidth of the controller, the parallel compensation grid, respectively, performs as the capacitance characteristic and inductance characteristic in different high frequency range. Compared with the three-phase, three-wire system, an additional zero-sequence path exists in the three-phase four-wire split capacitor inverter (TFSCI) system, so that the existing high frequency resonance suppression methods will be not effective. Since the zero-sequence component is neglected, HFR will also occur, in addition to the positive-sequence component and the negative-sequence component. Therefore, in order to suppress the high frequency resonance caused by positive-sequence, negative-sequence and zero-sequence components, an impedance reshaping strategy based on current feedback is proposed in this paper. This proposed method can reshape the amplitude and phase of the inverter impedance in a high frequency range without affecting the performance of the fundamental frequency control and ensure that the inverter contains a sufficient phase margin. Additionally, the proposed method can reshape the impedance of TFSCI within a wide frequency range, which makes it able to cope with the challenge of the parallel compensation degree change. Theoretical analysis and experiments verify the availability of the proposed control strategy.

Impaired auditory discrimination and auditory-motor integration in hyperfunctional voice disorders

Hyperfunctional voice disorders (HVDs) are the most common class of voice disorders, consisting of diagnoses such as vocal fold nodules and muscle tension dysphonia. These speech production disorders result in effort, fatigue, pain, and even complete loss of voice. The mechanisms underlying HVDs are largely unknown. Here, the auditory-motor control of voice fundamental frequency (fo) was examined in 62 speakers with and 62 speakers without HVDs. Due to the high prevalence of HVDs in singers, and the known impacts of singing experience on auditory-motor function, groups were matched for singing experience. Speakers completed three tasks, yielding: (1) auditory discrimination of voice fo; (2) reflexive responses to sudden fo shifts; and (3) adaptive responses to sustained fo shifts. Compared to controls, and regardless of singing experience, individuals with HVDs showed: (1) worse auditory discrimination; (2) comparable reflexive responses; and (3) a greater frequency of atypical adaptive responses. Atypical adaptive responses were associated with poorer auditory discrimination, directly implicating auditory function in this motor disorder. These findings motivate a paradigm shift for understanding development and treatment of HVDs.

Modified Topology for Three-Phase Multilevel Inverters Based on a Developed H-Bridge Inverter

This paper proposes a modified three-phase inverter from the developed H-bridge structure having multilevel functionality. The proposed topology can generate 7-levels of phase voltages and 13-levels of line voltages. Simple control methods such as fundamental frequency control method can be applied to the proposed topology. By adding three single-phase transformers, galvanic isolation is created for use in three-phase Dynamic Voltage Restorer systems. The proposed three-phase inverter utilizes less number of components; dc sources, semiconductor switches and driver circuits. Lower rated power switches with reduced blocking voltages are also used. These attributes make the proposed topology less complex in-terms of architecture and control. Comprehensive analysis of the proposed three-phase multilevel inverter and other presented topologies are investigated with respect to levels of output voltage, driver circuit quantity, dc voltage count, total component quantity and standing voltage. Details of the appropriate control technique employed is explained. Finally, practicability of the proposed inverter is validated by simulation using EMTDC/PSCAD software and experimental prototype.

Influence of bilateral cochlear implants on vocal control

Receiving a cochlear implant (CI) can improve fundamental frequency (F0) control for deaf individuals, resulting in increased vocal pitch control. However, it is unclear whether using bilateral CIs, which often result in mismatched pitch perception between ears, will counter this benefit. To investigate this, 23 bilateral CI users were asked to produce a sustained vocalization using one CI, the other CI, both CIs, or neither. Additionally, a set of eight normal hearing participants completed the sustained vocalization task as a control group. The results indicated that F0 control is worse with both CIs compared to using the ear that yields the lowest vocal variability. The results also indicated that there was a large range of F0 variability even for the relatively stable portion of the vocalization, spanning from 6 to 46 cents. These results suggest that bilateral CIs can detrimentally affect vocal control.

FPA Optimized Selective Harmonic Elimination in Symmetric–Asymmetric Reduced Switch Cascaded Multilevel Inverter

Symmetrical and asymmetrical multilevel inverters (MLIs) have demonstrated its usefulness in a wide range of applications. This is accomplished due to the ongoing improvement by reducing the converter size and enhancement in the voltage quality. In this article, a generalized cascaded MLI structure is developed, which can operate in both symmetric and asymmetric modes. Comparative assessment in terms of the number of components and voltage stress warrants the design superiority. A new selective harmonic elimination (SHE) control using flower pollination algorithm (FPA) is investigated for the developed asymmetrical MLI. The salient features of the FPA such as less burdensome compilation and ability tos single-stage local and global search ascertain the elimination of the targeted harmonics through optimum angles computation. Moreover, the competence of the FPA is verified by comparing it with well-known SHE algorithms. Simulation analysis is carried out in MATLAB/Simulink environment, which validates the workability of the developed system. Experimental tests using fundamental and high switching frequency control techniques are further conducted under a dynamic environment to demonstrate the efficacy of the proposed methodology.

Free vibration analysis of hybrid laminated composite cylindrical shells reinforced with shape memory alloy fibers

In the present paper, vibration behavior of hybrid laminated composite cylindrical shells reinforced with shape memory alloy fibers is investigated. Material properties of shape memory alloy fibers and composites are accurately considered temperature dependent. Thermo-mechanical properties of shape memory alloy fibers with uniform temperature change are calculated using Brinson’s one-dimensional constitutive law. Love’s first approximation and first-order shear deformation theory of shells with the von Kármán type of geometrical non-linearity are used in conjunction with Hamilton’s principle for deriving the equations of motion. The generalized differential quadrature method is employed to solve the coupled partial differential equations. The effects of pre-strain, volume fraction, phase transformation, location of shape memory alloy fibers, boundary conditions and temperature on the fundamental frequency of the hybrid laminated composite cylindrical shells are studied. Results indicate that a small amount of shape memory alloy fibers significantly increases the fundamental frequency and vibration control of the hybrid laminated composite reinforced with shape memory alloy hybrid laminated composite cylindrical shells.

Free vibration analysis of laminated composite conical shells reinforced with shape memory alloy fibers

In the present paper, for the first time the vibration behavior of hybrid composite conical shells reinforced with shape memory alloy (SMA) fibers is investigated. The temperature-dependent properties of SMA fibers and composite are accurately considered. Using the one-dimensional constitutive law of Brinson, thermo-mechanical properties such as recovery stresses, elasticity modulus and shear modulus with uniform temperature change are calculated for SMA fibers. Love’s first approximation classical shell theory with von-Karman type of geometrical nonlinearity is used in conjunction with Hamilton’s principle for deriving the equations of motion. A semi-analytical solution is presented so that trigonometric functions are applied in the circumferential direction, and the generalized differential quadrature method is used to discretize the equations of motion along the longitudinal direction. Finally, parametric studies are done to investigate the effects of volume fraction, pre-strain, location of SMA fibers, boundary conditions, semi-vertex angle of the cone, and temperature on the vibration characteristics of the SMA hybrid composite conical shells. It is shown that a proper utilization of SMA fibers significantly increases the fundamental frequency and vibration control of the SMA hybrid composite conical shells.

Control of Fundamental Frequency in Dysphonic Patients During Phonation and Speech

PurposeThe pitch-shift reflex (PSR) is the adaptation of the fundamental frequency during phonation and speech and describes the auditory feedback control. Speakers without voice and speech disorders mostly show a compensation of the pitch change in the auditory feedback and adapt their fundamental frequency to the opposite direction. Dysphonic patients often display problems with the auditory perception and control of their voice during therapy. Our study focuses on the auditory and kinesthetic control mechanisms of patients with muscle tension dysphonia (MTD) and speakers without voice and speech problems. Main purpose of the study is the analysis of the functionality of the control mechanisms within phonation and speech between patients with MTD and normal speakers. MethodSixty-one healthy subjects (17 male, 44 female) and 22 patients with MTD (7 male, 15 female) participated following two paradigms including a sustained phonation (vowel /a/) and speech ([‘mama]). Within both paradigms the fundamental frequency of the auditory feedback was increased synthetically. For the analysis of the PSR the electroencephalogram, electroglottography, the voice signal, and the high-speed endoscopy data were recorded simultaneously. The PSR in the electroencephalogram was detected via the N100 and the mismatch negativity. Statistical tests were applied for the detection of the PSR in the physiological response within the electroglottography, voice, and high-speed endoscopy signals. The results were compared between both groups. ResultsNo differences were found between the controls and patients with MTD regarding latency and magnitude of the perception of the pitch shift in both paradigms, but for the magnitude of the behavioral response. Differences also could be found for both groups between the “no pitch” and “pitch” condition of the two paradigms regarding vocal fold dynamics and voice quality. Patients with MTD showed more vibrational irregularities during the PSR than the controls, especially regarding the symmetry of vocal fold dynamics. ConclusionPatients with MTD seem to have a disturbed interaction between the auditory and kinesthetic feedback inducing the execution of an overriding behavioral response.

Japanese macaque phonatory physiology.

Although the call repertoire and its communicative function are relatively well explored in Japanese macaques (Macaca fuscata), little empirical data are available on the physics and the physiology of this species' vocal production mechanism. Here, a 6 year old female Japanese macaque was trained to phonate under an operant conditioning paradigm. The resulting 'coo' calls and spontaneously uttered 'growl' and 'chirp' calls were recorded with sound pressure level (SPL) calibrated microphones and electroglottography (EGG), a non-invasive method for assessing the dynamics of phonation. A total of 448 calls were recorded, complemented by ex vivo recordings on an excised Japanese macaque larynx. In this novel multidimensional investigative paradigm, in vivo and ex vivo data were matched via comparable EGG waveforms. Subsequent analysis suggests that the vocal range (range of fundamental frequency and SPL) of the macaque was comparable to that of a 7-10 year old human, with the exception of low intensity chirps, the production of which may be facilitated by the species' vocal membranes. In coo calls, redundant control of fundamental frequency in relation to SPL was also comparable to that in humans. EGG data revealed that growls, coos and chirps were produced by distinct laryngeal vibratory mechanisms. EGG further suggested changes in the degree of vocal fold adduction in vivo, resulting in spectral variation within the emitted coo calls, ranging from 'breathy' (including aerodynamic noise components) to 'non-breathy'. This is again analogous to humans, corroborating the notion that phonation in humans and non-human primates is based on universal physical and physiological principles.

Bioelectrical brain effects of one's own voice identification in pitch of voice auditory feedback.

Control of voice fundamental frequency (F0) relies in part on comparison of the intended F0 level and auditory feedback. This comparison impacts "sense of agency", or SoA, commonly defined as being the agent of one's own actions and plays a key role for self-awareness and social interactions. SoA is aberrant in several psychiatric disorders. Knowledge about brain activity reflecting SoA can be used in clinical practice for these disorders. It was shown that perception of voice feedback as one's own voice, reflecting the recognition of SoA, alters auditory sensory processing. Using a voice perturbation paradigm we contrasted vocal and bioelectrical brain responses to auditory stimuli that differed in magnitude: 100 and 400 cents. Results suggest the different magnitudes were perceived as a pitch error in self-vocalization (100 cents) or as a pitch shift generated externally (400 cents). Vocalizations and neural responses to changes in pitch of self-vocalization were defined as those made to small magnitude pitch-shifts (100 cents) and which did not show differential neural responses to upward versus downward changes in voice pitch auditory feedback. Vocal responses to large magnitude pitch shifts (400 cents) were smaller than those made to small pitch shifts, and neural responses differed according to upwards versus downward changes in pitch. Our results suggest that the presence of SoA for self-produced sounds may modify bioelectrical brain responses reflecting differences in auditory processing of the direction of a pitch shift. We suggest that this modification of bioelectrical response can be used as a biological index of SoA. Possible neuronal mechanisms of this modification of bioelectrical brain response are discussed.

Sensorimotor control of vocal pitch and formant frequencies in Parkinson's disease

BackgroundAuditory feedback reflects information on multiple speech parameters including fundamental frequency (pitch) and formant properties. Inducing auditory errors in these acoustic parameters during speech production has been used to examine the manner in which auditory feedback is integrated with ongoing speech motor processes. This integration has been shown to be impaired in disorders such as Parkinson's disease (PD), in which individuals exhibit difficulty adjusting to altered sensory-motor relationships. The current investigation examines whether such sensorimotor impairments affect fundamental frequency and formant parameters of speech differentially. MethodsWe employed a sensorimotor compensation paradigm to investigate the mechanisms underlying the control of vocal pitch and formant parameters. Individuals with PD and age-matched controls prolonged a speech vowel in the context of a word while the fundamental or first formant frequency of their auditory feedback was altered unexpectedly on random trials, using two magnitudes of perturbation. ResultsCompared with age-matched controls, individuals with PD exhibited a larger compensatory response to fundamental frequency perturbations, in particular in response to the smaller magnitude alteration. In contrast, the group with PD showed reduced compensation to first formant frequency perturbations. ConclusionsThe results demonstrate that the neural processing impairment of PD differentially affects the processing of auditory feedback for the control of fundamental and formant frequency. The heightened modulation of fundamental frequency in response to auditory perturbations may reflect a change in sensory weighting due to somatosensory deficits associated with the larynx, while the reduced ability to modulate vowel formants may result from impaired activation of the oral articulatory musculature.

Pitch control in professional and amateur singers

One aspect of major relevance to singing is the control of fundamental frequency. Ten amateur and ten professional singers sang two-octave arpeggi with three different levels of external auditory feedback, two tempi and two articulations (legato or staccato). The effects on pitch inaccuracy (defined as the distance in cents between the reference note and the sung note) of the following conditions were evaluated: (1) level of external feedback, (2) tempo (slow or fast), (3) articulation (legato or staccato), (4) tessitura (low, medium, or high), and (5) semi-phrase direction (ascending or descending). It was observed that inaccuracy was greatest in the descending semi-phrase arpeggi produced at a fast tempo and with a staccato articulation, especially for non-professional singers. The magnitude of inaccuracy was also relatively large in the high tessitura relative to the low and medium tessitura for such singers. Counter to predictions, when external auditory feedback was strongly attenuated or canceled by the hearing protectors, non-professional singers showed greater pitch accuracy than in the other external feedback conditions, which indicates the importance of internal auditory feedback in pitch control. With an increase in training, the singer's pitch inaccuracy decreases.

Effect of Training and Level of External Auditory Feedback on the Singing Voice: Pitch Inaccuracy

One of the most important aspects of singing is the control of fundamental frequency. The effects on pitch inaccuracy, defined as the distance in cents in equally tempered tuning between the reference note and the sung note, of the following conditions were evaluated: (1) level of external feedback, (2) tempo (slow or fast), (3) articulation (legato or staccato), (4) tessitura (low, medium, or high), and (5) semi-phrase direction (ascending or descending). The subjects were 10 nonprofessional singers and 10 classically trained professional or semi-professional singers (10 men and 10 women). Subjects sang one octave and a fifth arpeggi with three different levels of external auditory feedback, two tempi, and two articulations (legato or staccato). It was observed that inaccuracy was greatest in the descending semi-phrase arpeggi produced at a fast tempo and with a staccato articulation, especially for nonprofessional singers. The magnitude of inaccuracy was also relatively large in the high tessitura relative to the low and the medium tessitura for such singers. Contrary to predictions, when external auditory feedback was strongly attenuated by the hearing protectors, nonprofessional singers showed greater pitch accuracy than in the other external feedback conditions. This finding indicates the importance of internal auditory feedback in pitch control. With an increase in training, the singer's pitch inaccuracy decreases.

Predictive Harmonic Control and Its Optimal Digital Implementation for MMC-Based Active Power Filter

An optimal active power filter (APF) based on modular multilevel converter (MMC) without load current and lower arm current sensors is proposed. Its control algorithm mainly includes predictive harmonic current control, fundamental frequency control, and dc voltage control. Comparing to direct current control, the first two subcontrollers transfer the harmonic and fundamental active/reactive power current to voltage references, which are suitable to generate the modulation signals to MMCs as well as two-level converters. Their full digital optimization structures combined with the MMC voltage and current control are detail discussed and implemented on field programmable gate array. The synthesis result indicates a low hardware resource utilization and calculation delay of the designed controller. The experimental results on an MMC-based APF prototype verified the static and dynamic performances of the proposed algorithm.

Control Strategy to Naturally Balance Hybrid Converter for Variable-Speed Medium-Voltage Drive Applications

In this paper, a novel control strategy to naturally balance a hybrid converter is presented for medium-voltage induction motor drive applications. Fundamental current of the motor is produced by a three-level quasi-square-wave converter. Several single-phase full-bridge converters are connected in series with this quasi-square-wave converter to eliminate harmonic voltages from the net output voltage of this hybrid converter. Various novel modulation strategies for these series cells are proposed. These lead to a naturally regulated dc-bus voltage of series cells. These also optimize the number of series cells required. Variable fundamental voltage and frequency control of induction motor is adopted with a constant dc-bus voltage of the three-level quasi-square-wave converter. Experimental results are also produced here to validate the proposed modulation strategies for induction motor drives using low-voltage protomodel. Based on the aforementioned, a 2.2-kV induction motor drive has been built, and results are also produced in this paper.

The influence of attentional focus on voice control

The present study tested the role of attentional focus on control of voice fundamental frequency (F0). Subjects vocalized an “ah” sound while hearing their voice auditory feedback randomly shifted upwards or downwards in pitch. In the “UP” condition, subjects vocalized, listened for and pressed a button for each upward pitch shift stimulus. In the “DOWN” condition, subjects listened for and pressed a button for each downward shift. In the CONTROL condition, subjects vocalized without paying attention to the stimulus direction or pressing a button. Data were analyzed by averaging voice F0 contours across several trials for each pitch shift stimulus in all conditions. Response magnitudes were larger for the CONTROL than for the UP or DOWN conditions. Responses for the UP and DOWN conditions did not differ. Results suggest that when subjects focus their attention to identify specific stimuli and produce a non-vocal motor response conditional upon the identification, the neural mechanisms involved in voice control are reduced, possibly because of a reduction in the error signal resulting from the comparison of the efference copy of voice output with auditory feedback. Thus, focusing attention away from vocal control reduces neural resources involved in control of voice F0.