Showing papers on "Fundamental frequency published in 2010"

Adaptive Harmonic Spectral Decomposition for Multiple Pitch Estimation

Abstract: Multiple pitch estimation consists of estimating the fundamental frequencies and saliences of pitched sounds over short time frames of an audio signal. This task forms the basis of several applications in the particular context of musical audio. One approach is to decompose the short-term magnitude spectrum of the signal into a sum of basis spectra representing individual pitches scaled by time-varying amplitudes, using algorithms such as nonnegative matrix factorization (NMF). Prior training of the basis spectra is often infeasible due to the wide range of possible musical instruments. Appropriate spectra must then be adaptively estimated from the data, which may result in limited performance due to overfitting issues. In this paper, we model each basis spectrum as a weighted sum of narrowband spectra representing a few adjacent harmonic partials, thus enforcing harmonicity and spectral smoothness while adapting the spectral envelope to each instrument. We derive a NMF-like algorithm to estimate the model parameters and evaluate it on a database of piano recordings, considering several choices for the narrowband spectra. The proposed algorithm performs similarly to supervised NMF using pre-trained piano spectra but improves pitch estimation performance by 6% to 10% compared to alternative unsupervised NMF algorithms.

Dynamic Phasor and Frequency Estimates Through Maximally Flat Differentiators

Abstract: Estimates of the dynamic phasor and its derivatives are obtained through the weighted least squares solution of a Taylor approximation using classical windows as weighting factors. This solution leads to differentiators with ideal frequency response around the fundamental frequency and to very low sidelobe level over the stopband, which implies low noise sensitivity. The differentiators are maximally flat in the interval centered at the fundamental frequency and have a linear phase response. Therefore, their estimates are free of amplitude and phase distortion and are obtained at once. No further patch is needed to improve their accuracy. Examples of dynamic phasor estimates are illustrated under transient conditions. Special emphasis is put on frequency measurements.

Multiple Fundamental Frequency Estimation by Modeling Spectral Peaks and Non-Peak Regions

Abstract: This paper presents a maximum-likelihood approach to multiple fundamental frequency (F0) estimation for a mixture of harmonic sound sources, where the power spectrum of a time frame is the observation and the F0s are the parameters to be estimated. When defining the likelihood model, the proposed method models both spectral peaks and non-peak regions (frequencies further than a musical quarter tone from all observed peaks). It is shown that the peak likelihood and the non-peak region likelihood act as a complementary pair. The former helps find F0s that have harmonics that explain peaks, while the latter helps avoid F0s that have harmonics in non-peak regions. Parameters of these models are learned from monophonic and polyphonic training data. This paper proposes an iterative greedy search strategy to estimate F0s one by one, to avoid the combinatorial problem of concurrent F0 estimation. It also proposes a polyphony estimation method to terminate the iterative process. Finally, this paper proposes a postprocessing method to refine polyphony and F0 estimates using neighboring frames. This paper also analyzes the relative contributions of different components of the proposed method. It is shown that the refinement component eliminates many inconsistent estimation errors. Evaluations are done on ten recorded four-part J. S. Bach chorales. Results show that the proposed method shows superior F0 estimation and polyphony estimation compared to two state-of-the-art algorithms.

A Generalized Delayed Signal Cancellation Method for Detecting Fundamental-Frequency Positive-Sequence Three-Phase Signals

Abstract: A novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage vector based on a generalization of the delayed signal cancellation method is proposed in this paper. The technique is implemented by sampling and storing the instantaneous αβ voltage vector. A mathematical transformation is then proposed through which the current and delayed voltage vectors are combined. It is shown that the proposed transformation has unity gain for the fundamental-frequency positive-sequence voltage vector, while its gain is equal to zero for some chosen components. Cascaded transformations can then be used for eliminating the fundamental-frequency negative-sequence vector, as well as chosen positive- and negative-sequence harmonic vector components and, thus, for accurately obtaining the fundamental-frequency positive-sequence voltage vector. The output of the last transformation block is input to a synchronous reference frame phase-locked loop for detecting frequency and position of the positive-sequence vector. A proposal for making the scheme frequency adaptive is also presented. The good performance of the proposed method is verified with simulations and experiments by using distorted and unbalanced signals, containing fundamental-frequency as well as positive- and negative-sequence harmonic components. The proposed method frequency adaptation capability is also verified.

Guidelines for Selecting Microphones for Human Voice Production Research

Abstract: Purpose This tutorial addresses fundamental characteristics of microphones (frequency response, frequency range, dynamic range, and directionality), which are important for accurate measurements of voice and speech. Method Technical and voice literature was reviewed and analyzed. The following recommendations on desirable microphone characteristics were formulated: The frequency response of microphones should be flat (i.e., variation of less than 2 dB) within the frequency range between the lowest expected fundamental frequency of voice and the highest spectral component of interest. The equivalent noise level of the microphones is recommended to be at least 15 dB lower than the sound level of the softest phonations. The upper limit of the dynamic range of the microphone should be above the sound level of the loudest phonations. Directional microphones should be placed at the distance that corresponds to their maximally flat frequency response, to avoid the proximity effect; otherwise, they will be unsuit...

Broadband vibration-based energy harvesting improvement through frequency up-conversion by magnetic excitation

Abstract: Traditional vibration-based energy harvesters are designed for a specific base excitation frequency by matching its fundamental natural frequency. This work presents the modeling and analysis of a nonlinear, magnetically excited energy harvester that exhibits efficient broadband, frequency-independent performance utilizing a passive auxiliary structure that remains stationary relative to the base motion. This system is especially effective in the regime of driving frequencies well below its fundamental frequency, thus enabling a more compact design solution over traditional topologies. A model based on Euler–Bernoulli beam theory is coupled to a linear circuit and a model of the nonlinear, magnetic interaction to produce a distributed parameter magneto-electromechanical system. This model is used in both harmonic and stochastic base excitation case studies. The results of these simulations demonstrate multiple-order-of-magnitude power harvesting performance improvement at low driving frequencies and an insensitivity to time-varying base excitation. Furthermore, the proposed system is shown to outperform an optimally designed, standard energy harvester in the presence of broadband, random base excitation.

A high-performance top-gate graphene field-effect transistor based frequency doubler

Abstract: A high-performance top-gate graphene field-effect transistor (G-FET) is fabricated, and used for constructing a high efficient frequency doubler. Taking the advantages of the high gate efficiency and low parasitic capacitance of the top-gate device geometry, the gain of the graphene frequency doubler is increased about ten times compared to that of the back-gate G-FET based device. The frequency response of the frequency doubler is also pushed from 10 kHz for a back-gate device to 200 kHz, at which most of the output power is concentrated at the doubled fundamental frequency of 400 kHz.

A General Model for Estimating the Laminated Steel Losses Under PWM Voltage Supply

Abstract: The new model is based on a modified Steinmetz equation and employs a hysteresis-loss multiplicative coefficient and a combined coefficient for eddy-current and excess losses, both coefficients being variable with induction and frequency. The material model coefficients are first identified through multifrequency tests with sine-wave excitation. The iron-loss increase due to pulsewidth-modulation supply is estimated using global waveform parameters of the nonsinusoidal voltage. The study includes three different grades of non-grain-oriented electric steel. The data cover a wide range of fundamental frequency from 10 to 600 Hz and induction from 0.05 to 2 T. The errors of the computational model are small at relatively low fundamental frequency and increase thereafter. The main advantages of the model are its simplicity of use and minimal data requirements.

Vocal Melody Extraction in the Presence of Pitched Accompaniment in Polyphonic Music

Abstract: Melody extraction algorithms for single-channel polyphonic music typically rely on the salience of the lead melodic instrument, considered here to be the singing voice. However the simultaneous presence of one or more pitched instruments in the polyphony can cause such a predominant-F0 tracker to switch between tracking the pitch of the voice and that of an instrument of comparable strength, resulting in reduced voice-pitch detection accuracy. We propose a system that, in addition to biasing the salience measure in favor of singing voice characteristics, acknowledges that the voice may not dominate the polyphony at all instants and therefore tracks an additional pitch to better deal with the potential presence of locally dominant pitched accompaniment. A feature based on the temporal instability of voice harmonics is used to finally identify the voice pitch. The proposed system is evaluated on test data that is representative of polyphonic music with strong pitched accompaniment. Results show that the proposed system is indeed able to recover melodic information lost to its single-pitch tracking counterpart, and also outperforms another state-of-the-art melody extraction system designed for polyphonic music.

A new seismic isolation system and its feasibility study

Abstract: This paper introduces a new seismic isolation system called a periodic foundation (PF), where inclusions are periodically arranged. The PF is different from traditional base isolation in that it causes a fundamental frequency shift in the structure, thus reducing its response and generating a frequency gap. If the frequency contents of a seismic wave fall into the gap, it can not propagate in the foundation. Thus, it will exert no influence on the structure above. A systematic study of the band of frequency gap for a 2D PF is conducted. The influence of physical and geometrical parameters such as density and elastic modulus as well as filling fraction of the PF and its materials on the band of frequency gap are investigated, and a design with a frequency gap as low as 2.49–3.72 Hz is achieved. This band of frequency gap corresponds well to the design spectra in earthquake engineering. Numerical simulations of a six-story frame structure with different foundations demonstrate that a proposed PF can greatly reduce the seismic response of an isolated structure. This investigation shows that PFs have great potential in future applications of seismic isolation technology.

Processing of Harmonics and Interharmonics Using an Adaptive Notch Filter

Abstract: A method for real-time detection and extraction of individual harmonic and interharmonic components in a power signal with potentially time-varying characteristics is presented. The proposed method, which is based on the concept of adaptive notch filter (ANF), adaptively decomposes the measured power signal into its constituting components independent of where their frequencies are located. The algorithm provides instantaneous values of the various estimated frequency components in addition to the values of their frequencies, amplitudes, and phase angles. The structure and mathematical formulation of the proposed technique, including guidelines for its parameter tuning, are presented and its performance is studied in a variety of scenarios where the power signal attributes, such as fundamental frequency and amplitude, undergo variations over time. This study confirms the desirable transient and steady-state performances of the proposed method. Compared with its recently proposed counterpart, the proposed method of this paper obviates the need for using a phase-locked loop (PLL), and hence, offers a more simplified structure which makes it more attractive from an implementation point of view.

Frequency Shift of Carbon-Nanotube-Based Mass Sensor Using Nonlocal Elasticity Theory

Abstract: The frequency equation of carbon-nanotube-based cantilever sensor with an attached mass is derived analytically using nonlocal elasticity theory. According to the equation, the relationship between the frequency shift of the sensor and the attached mass can be obtained. When the nonlocal effect is not taken into account, the variation of frequency shift with the attached mass on the sensor is compared with the previous study. According to this study, the result shows that the frequency shift of the sensor increases with increasing the attached mass. When the attached mass is small compared with that of the sensor, the nonlocal effect is obvious and increasing nonlocal parameter decreases the frequency shift of the sensor. In addition, when the location of the attached mass is closer to the free end, the frequency shift is more significant and that makes the sensor reveal more sensitive. When the attached mass is small, a high sensitivity is obtained.

Output from a Josephson stimulated terahertz amplified radiation emitter.

Abstract: The angular dependence of the radiation-zone output power and electric polarization of stimulated terahertz amplified radiation (STAR) emitted from a dc voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions is calculated. The boundary conditions are obtained from Love’s equivalence principles. During coherent emission, a spatially uniform ac Josephson current density in the stack acts as a surface electric current density antenna source, leading to a harmonic radiation frequency spectrum, as in experiment, but absent in all cavity models of cylindrical mesas. Spatial fluctuations of the ac Josephson current allow its fundamental mode to lock onto the lowest finite energy cylindrical cavity mode, causing it to resonate, leading to a non-uniform magnetic surface current density radiation source, and a non-trivial combined fundamental frequency output power with linear polarization for general radiation directions, which may be fully or partially coherent. The higher ac Josephson harmonics do not excite other cylindrical cavity modes. For rectangular mesas, the lowest energy modes are empirically not excited, but the non-uniform ac Josephson current can excite the harmonic sequence of modes with spatial variation across the rectangular widths, leading to combined radiation outputs both for the fundamental and the higher harmonics, which combinations also may be either fully or partially coherent. The superconducting substrate is modeled as a perfect magnetic conductor, greatly reducing the STAR emitter power and modifying its angular dependence, especially parallel to the substrate. Based upon this substrate model, existing Bi2Sr2CaCu2O8+δ crystals atop perfect electric conductors could have STAR emitter power in excess of 5 mW, acceptable for many device applications. (Some figures in this article are in colour only in the electronic version)

Characterization of GaN HEMT Low-Frequency Dispersion Through a Multiharmonic Measurement System

Abstract: In this paper, the experimental characterization of low-frequency dispersion (i.e., long-term memory effects) affecting microwave GaN HEMTs is carried out by adopting a new nonlinear measurement system, which is based on low-frequency multiharmonic signal sources. The proposed setup, which has been fully automated by a control software procedure, enables given source/load device terminations at fundamental and harmonic frequencies to be synthesized. Different experimental results are provided to characterize well-known effects related to low-frequency dispersion (e.g., knee walkout and drain current collapse) and to demonstrate the validity of assumptions commonly adopted for electron device modeling.

Nonlinear vibrational analysis of single-layer graphene sheets.

Abstract: Recent experiments have shown the applicability of single-layer graphene sheets (SLGSs) as electromechanical resonators. Existing theoretical models, based on linear continuum or atomistic methods, are limited to the study of linear vibrations of SLGSs. Here we introduce a hybrid atomistic-structural element which is capable of modelling nonlinear behaviour of graphene sheets. This hybrid element is based on an empirical inter-atomic potential function and can model the nonlinear dynamic response of SLGSs. Using this element, nonlinear vibrational analysis of SLGSs is performed. It is shown that the nonlinear vibrational analysis of SLGSs predicts significantly higher fundamental frequencies. Also, the effects of vibration amplitude as well as the geometry of the SLGSs on the fundamental frequency are studied and predictive relations between the fundamental frequency, the SLGS length and the non-dimensional vibration amplitude are presented. The results are verified with experimental observations and are in remarkable agreement.

Second harmonic generation in metamaterials based on homogeneous centrosymmetric nanowires

Abstract: We present a comprehensive theoretical study of the second harmonic generation (SHG) in metamaterials consisting of arbitrary distributions of cylindrical nanowires made of centrosymmetric materials. The electromagnetic field at both the fundamental frequency (FF) and second harmonic (SH), as well as the total cross section, the absorption cross section, and the scattering cross section, are calculated by means of a numerical algorithm based on the multiple scattering method. Our algorithm fully describes the nonlinear optical response of the metamaterial by incorporating the contributions of both the surface and bulk nonlinear polarizations and can be applied to both s- and p-polarized incident waves. We use this numerical method to investigate the SHG in a series of particular cases of practical interest, namely, a single metallic cylinder, chains of metallic cylinders, and periodic and random distributions of such cylinders. In particular, we study the relation between the local field enhancement, via the excitation of surface plasmon-polariton modes, and the amount of energy absorbed or scattered in the far-field, at the FF and the SH.

Spatiotemporal representation of the pitch of harmonic complex tones in the auditory nerve.

Abstract: The pitch of harmonic complex tones plays an important role in speech and music perception and the analysis of auditory scenes, yet traditional rate–place and temporal models for pitch processing provide only an incomplete description of the psychophysical data. To test physiologically a model based on spatiotemporal pitch cues created by the cochlear traveling wave (Shamma, 1985), we recorded from single fibers in the auditory nerve of anesthetized cat in response to harmonic complex tones with missing fundamentals and equal-amplitude harmonics. We used the principle of scaling invariance in cochlear mechanics to infer the spatiotemporal response pattern to a given stimulus from a series of measurements made in a single fiber as a function of fundamental frequency F0. We found that spatiotemporal cues to resolved harmonics are available for F0 values between 350 and 1100 Hz and that these cues are more robust than traditional rate–place cues at high stimulus levels. The lower F0 limit is determined by the limited frequency selectivity of the cochlea, whereas the upper limit is caused by the degradation of phase locking to the stimulus fine structure at high frequencies. The spatiotemporal representation is consistent with the upper F0 limit to the perception of the pitch of complex tones with a missing fundamental, and its effectiveness does not depend on the relative phase between resolved harmonics. The spatiotemporal representation is thus consistent with key trends in human psychophysics.

Comparison between seismic vulnerability models and experimental dynamic properties of existing buildings in France

Abstract: Elastic fundamental frequency is a key-parameter of simplified seismic design and vulnerability assessment methods. Empirical relationships exist in codes to estimate this frequency but they miss experimental data to validate them accounting for national feature of building design and, above all, corresponding uncertainties. Even if resonance frequency extracted from ambient vibrations may be larger than the elastic frequency (at yield) generally used in earthquake engineering, ambient vibration recordings may provide a large set of data for statistical analysis of periods versus building characteristics relationships. We recorded ambient vibrations and estimated the fundamental frequency of about 60 buildings of various types (RC and masonry) in Grenoble City (France). These data complete the set existing yet, made of 26 RC-buildings of Grenoble (Farsi and Bard 2004) and 28 buildings in Nice (France) (Dunand 2005). Statistical analysis of these experimental data was performed for fundamental frequencies of RC shear wall structures and the results are compared with existing relationships. Only building height or number of stories has a statistical relevancy to estimate the resonance frequency but the variability associated to the proposed relationships is large. Moreover, we compared the elastic part of capacity curves of RC and masonry buildings used in the European Risk-UE method for vulnerability assessment with the experimental frequencies. The variability is also large and the curves may not be consistent with French existing buildings.

Combined matching and filter circuit

Abstract: A combined matching and harmonic rejection circuit with increased harmonic rejection provided by a split resonance for one or more of the capacitive or inductive elements of the circuit. At a fundamental frequency, the circuit comprises an inductive series arm with capacitive shunt arms. The capacitance of a shunt arm may be provided by two or more parallel paths, each having a capacitor and an inductor in series so that, in addition to providing the effective capacitance necessary for impedance matching at the fundamental frequency, two separate harmonics represented by the series resonances of the parallel paths are rejected. In this manner, an extra null in the circuit's stop-band may be achieved using the same number of shunt elements necessary to achieve impedance matching at the fundamental frequency.

Tissue harmonic imaging.

Abstract: Ultrasound wave travels faster in compressive phase and slower during rarefaction (reduced particle density). This nonlinear propagation changes a part of the beams energy to harmonic frequencies. The second harmonic has a frequency which is twice the fundamental frequency and contains most of the harmonic energy. Harmonics are not produced in the superficial part of tissue. Harmonics are most prominent in the central section of the transmitted beam. Hence lateral resolution is improved in harmonic mode Reduced Image artefacts like reverberations, side and grating lobes Improved contrast resolution as less “noise” and clutter (better signal to noise ratio).

Current Differential Protection of Transmission Line Using the Moving Window Averaging Technique

Abstract: We propose a new approach to current differential protection of transmission lines. In this approach, we transform the instantaneous line current(s) by using a moving window averaging technique. If the time span of moving window is equal to one-cycle time, then the steady-state value of the transformed current is zero for a periodic signal which is composed of fundamental and harmonic frequencies. Signal distortions (e.g., a fault) cause the transformed currents to deviate from the nominal zero value. This permits the development of a sensitive, secure, fast, and yet simple current differential protection scheme. The scheme can be applied in toto to series-compensated transmission lines. Results on a four-machine ten-bus system and comparative evaluation with state-of-the-art methods brings out promise of the proposed method.

Subharmonics analysis of nonlinear flexural vibrations of piezoelectrically actuated microcantilevers

Abstract: Using the method of multiple scales, an extensive frequency response and subharmonic resonance analysis of the equations of motion governing the nonlinear flexural vibrations of piezoelectrically actuated microcantilevers is performed. Such comprehensive understanding of the nonlinear response and subharmonics analysis of these microcantilevers is, indeed, justified by the applications of piezoelectrically actuated microcantilevers that are increasingly becoming popular in many science and engineering areas including scanning force microscopy, biosensors, and microactuators. Along this line, the method of multiple scales is used to derive the 2× and 3× subharmonic resonances appearing in nonlinear flexural vibrations of a piezoelectrically actuated microcantilever. An experimental examination is performed in order to verify the analytical results. The analytical and experimental results yield the same system response for the fundamental frequency. In addition, the experimental results demonstrate the presence of subharmonic resonances that are supported by numerical simulations of the equations of motion. The experimental mode shapes of these subharmonic frequencies are also measured and compared with fundamental frequency.

Electric Traction Power System Stability : Low-frequency interaction between advanced rail vehicles and a rotary frequency converter

Abstract: Low-frequency instability in AC electric traction power systems has come to be a concern in recent years. Power oscillations in the range of 10-30 % of the system’s fundamental frequency are report ...

Nonlinear Ultrasonic Investigation of Concrete Damaged under Uniaxial Compression Step Loading

Abstract: This research explains an experimental investigation of the concrete applying nonlinear ultrasonic testing technique. Eighteen cubic specimens, 150 150 150 mm, were prepared from three concrete batches with w/c of 40, 50, and 60%, respectively. The hardened concrete specimens after 28-day of curing were simultaneously subjected to uniaxial compression and nonlinear ultrasonic testing. The specimens were damaged by gradually loading them in compression in several steps representing 0, 20, 40, 60, and 80%, respectively, of the specimen's ultimate strength. At the end of each loading step ultrasonic evaluation was performed and the time domain waveforms were recorded at different power levels. Fast Fourier transformation FFT of the time domain waveforms was conducted to produce the frequency spectra. The data obtained from frequency spectra was used to study the change in signal amplitude or signal attenuation. It was found that attenuation is quite sensitive to different damage and power levels. The Fourier amplitudes obtained from FFT of the time domain data were normalized at fundamental frequency. Normalized spectra were used to examine the generation of second harmonic wave components. It was also found that the formation of second harmonic components are highly sensitive to increase in damage and change in power levels.