Harmonic Envelope Research Articles

Laser-induced micro-cavity on a fiber end with a harmonic-Vernier effect for salinity sensing

In this paper, a fiber optic salinity sensor based on Fabry–Perot interference (FPI) with a harmonic-Vernier effect is suggested. An open cavity and a resin solid cavity are grown at the end of the fiber by a unique fiber-end photopolymerization and integration (FEPI) technique. When seawater fills the open cavity, it changes the optical path length (OPL) of the interferometer directly. While the OPL of the reference interferometer is hardly impacted by the seawater. The insertion of the harmonic envelope shifts greatly with salinity. Tunable sensing performances are achieved by adjusting the cavity length ratio(CLR) according to a theoretical model. The maximum sensitivity of 6.53 nm/‰is attained in the range of 25 ‰to 45 ‰when its CLR approaches 1.18. In addition, the measuring accuracy, consistency, and temperature compensation method are also experimentally investigated. The suggested sensor is a prospective competitor in the field of measuring the salinity of seawater due to the advantages of high sensitivity, compact size, large dynamic range, and adjustable capabilities.

Improved harmonic spectral envelope extraction for singer classification with hybridised model

Improved harmonic spectral envelope extraction for singer classification with hybridised model

Broadband and linearized photonic time-stretch analog-to-digital converter based on a compact dual-polarization modulator.

A broadband linearization scheme for a photonic time-stretch (PTS) analog-to-digital converter (ADC) is proposed based on a dual-polarization binary phase-shift keying (DP-BPSK) modulator with complementary parallel single-sideband (SSB) modulation. In this system, two stretched radio frequency signals, corresponding to the two orthogonal polarizations of the DP-BPSK modulator, are complementary, which can realize differential operation to eliminate the second-order harmonic distortion and pulse envelope distortion. Meanwhile, SSB modulation is used to avoid dispersion-induced power fading. Theoretical analysis and simulation results show that the proposed scheme can effectively improve the linear performance of PTS ADC, even considering the polarization-dependent delay deviation and amplitude offset.

The neural response at the fundamental frequency of speech is modulated by word-level acoustic and linguistic information.

Spoken language comprehension requires rapid and continuous integration of information, from lower-level acoustic to higher-level linguistic features. Much of this processing occurs in the cerebral cortex. Its neural activity exhibits, for instance, correlates of predictive processing, emerging at delays of a few 100 ms. However, the auditory pathways are also characterized by extensive feedback loops from higher-level cortical areas to lower-level ones as well as to subcortical structures. Early neural activity can therefore be influenced by higher-level cognitive processes, but it remains unclear whether such feedback contributes to linguistic processing. Here, we investigated early speech-evoked neural activity that emerges at the fundamental frequency. We analyzed EEG recordings obtained when subjects listened to a story read by a single speaker. We identified a response tracking the speaker's fundamental frequency that occurred at a delay of 11 ms, while another response elicited by the high-frequency modulation of the envelope of higher harmonics exhibited a larger magnitude and longer latency of about 18 ms with an additional significant component at around 40 ms. Notably, while the earlier components of the response likely originate from the subcortical structures, the latter presumably involves contributions from cortical regions. Subsequently, we determined the magnitude of these early neural responses for each individual word in the story. We then quantified the context-independent frequency of each word and used a language model to compute context-dependent word surprisal and precision. The word surprisal represented how predictable a word is, given the previous context, and the word precision reflected the confidence about predicting the next word from the past context. We found that the word-level neural responses at the fundamental frequency were predominantly influenced by the acoustic features: the average fundamental frequency and its variability. Amongst the linguistic features, only context-independent word frequency showed a weak but significant modulation of the neural response to the high-frequency envelope modulation. Our results show that the early neural response at the fundamental frequency is already influenced by acoustic as well as linguistic information, suggesting top-down modulation of this neural response.

Soliton based χ(2) combs in high-Q optical microresonators.

Investigations of the frequency combs in χ(3) microresonators have passed a critical point when the soliton based regimes are well established and realized on different platforms. For χ(2) microresonators, where the first harmonic (FH) and second harmonic (SH) envelopes are coupled via the SH generation and optical parametric oscillation, the comb-soliton studies are just starting. Here we report on a vast accessible dual χ(2) soliton-comb family in high-Q microresonators with the SH and FH combs centered at the pump frequency ωp and its half ωp/2. Vicinity of the point of equal FH and SH group velocities λc, available via proper radial poling, is found to be the most advantageous for the generation of spectrally broad dual FH-SH combs. Our predictions as applied to lithium niobate resonators include the dependence of comb and dissipative soliton parameters on the pump power, the deviation λp - λc, the modal quality factors and frequency detunings, and the necessary parameters of radial poling of the resonator. These predictions form a solid basis for the realization of χ(2) frequency combs.

Genetically related singers—acoustic feature analysis and impact on singer identification

Studies relating music with genetics have been one of the fascinating fields of research. In this study, we have attempted to answer the most curious question-how acoustically close are the genetically related singers? The present study has investigated this perception using two genetically different relations-three female sibling singers and father-son singer relation. These are famous Indian playback singers and the acoustic features are extracted using the songs of Bollywood films. Three different sets of self-developed cappella database are used for the experimentation. Positive correlations among the major musical aptitudes-pitch, vibrato, formant, and harmonic spectral envelope for both the singer relationships-revealed the genetic impact on the acoustic features. Also, the investigation of timbre spectral feature proved it a significant acoustic feature that differentiates similar voices. With Spearman's correlation coefficient, we conclude that strong acoustical association was observed between the acoustic features of genetically related singers, especially the female sibling singers. This was further validated by correlating these singers with genetically unrelated singers. A human perception test performed using cover songs indicated the genetic impact in voice similarity, while the automatic singer identification system discriminated singers more accurately than the human listeners.

Anti-Sweep-Jamming Method Based on the Averaging of Range Side Lobes for Hybrid Modulation Proximity Detectors

Hybrid modulation continuous waveform (HMCW) proximity detectors emit binary phase-coded chirp (BPCC) waveforms. Therefore, they possess the advantages of binary phase-coded modulation and chirp modulation simultaneously. To enhance the anti-sweep-jamming performance of HMCW detectors, this paper analyses the response of an HMCW detector under sweep jamming and proposes an anti-jamming method based on the novel average range side lobe (ARS) approach. Similar to the instant correlation with harmonic demodulation (ICHD) method, the ARS method also combines time-domain instantaneous correlation with frequency-domain harmonic demodulation to obtain the range information of the target. The difference is that the ARS method uses a fast Fourier transform (FFT) instead of a band pass filter (BPF) to extract the harmonic envelope and averages multiple harmonic coefficients obtained via the FFT. Because the correlation side lobes of chaotic codes follow a Gaussian distribution, the output of an HMCW detector under sweep jamming is suppressed after ARS processing. The proposed method is proven to be feasible and effective through numerical simulations. The results show that the ARS method offers improved anti-sweep-jamming performance.

Robust singer identification of Indian playback singers

Singing voice analysis has been a topic of research to assist several applications in the domain of music information retrieval system. One such major area is singer identification (SID). There has been enormous increase in production of movies and songs in Bollywood industry over the last 50 decades. Surveying this extensive dataset of singers, the paper presents singer identification system for Indian playback singers. Four acoustic features namely—formants, harmonic spectral envelope, vibrato, and timbre—that uniquely describe the singer are extracted from the singing voice segments. Using the combination of these multiple acoustic features, we address the major challenges in SID like the variations in singer’s voice, testing of multilingual songs, and the album effect. Systematic evaluation shows the SID is robust against the variations in singer’s singing style and structure of songs and is effective in identifying the cover songs and singers. The results are investigated on in-house cappella database consisting of 26 singers and 550 songs. By performing dimension reduction of the feature vector and using Support Vector Machine classifier, we achieved an accuracy of 86% using fourfold cross validation process. In addition, performance comparison of the proposed work with other existing approaches reveals the superiority in terms of volume of dataset and song duration.

Critical Parameter Design for a Cascaded H-Bridge With Selective Harmonic Elimination/Compensation Based on Harmonic Envelope Analysis for Single-Phase Systems

This paper investigates the critical parameter design technique for a cascaded H-Bridge (CHB) with selective harmonic elimination (SHE)/compensation (SHC) for single-phase systems. The critical parameters include the filter inductance, the number of H-bridge cells, the dc-bus voltage and the switching frequency. This paper derives the relationship of electrical parameters, topologies, and modulation techniques to the voltage/current harmonic envelopes, and compares the filter inductor design for an H-Bridge with sinusoidal pulsewidth modulation (SPWM), an H-Bridge (HB) with SHE/SHC and a CHB with SHE/SHC. Furthermore, a harmonic-envelope-based approach is developed to determine the optimum design parameters. The developed approach designs the harmonic envelope with two proposed criteria: the first one is the capacity criterion, which guarantees that the fundamental and controllable components are within the applicable solution range to avoid overmodulation; the other one is the attenuation criterion, which ensures that the uncontrollable harmonic complies with the grid limit. Simulations and experiments verified that a CHB designed with the proposed technique can simultaneously fulfill the compensation objectives and meet the harmonic limits.

Power quality grid code compliance for renewable power plants in South Africa

The introduction of renewable generation to South Africa's grid has introduced challenges to the management and regulation of power quality (PQ). These have been addressed by establishing PQ compliance criteria in line with local circumstances and by the introduction of a Power Quality Guideline for renewable power plants (RPPs). A key challenge to RPPs has been meeting emission limits for harmonics. This has been addressed in South Africa's RPP Guideline by the development and introduction of a Group Harmonic Distortion limit which provides some flexibility to RPPs in making individual harmonic emission limits. The use of 95th percentile harmonic impedance envelopes is discussed and recommendations for impedance envelopes are made for different voltage levels within the South African Grid, based on actual network data. A lesson learnt is that using international standards and guidelines provides a starting point for compliance rules when introducing renewable generation. Developing countries that share economic and electricity network characteristics with South Africa should tailor the PQ rules and guidelines for RPPs to meet local conditions.

Electric and acoustic harmonic integration predicts speech-in-noise performance in hybrid cochlear implant users

BackgroundPitch perception of complex tones relies on place or temporal fine structure-based mechanisms from resolved harmonics and the temporal envelope of unresolved harmonics. Combining this information is essential for speech-in-noise performance, as it allows segregation of a target speaker from background noise. In hybrid cochlear implant (H-CI) users, low frequency acoustic hearing should provide pitch from resolved harmonics while high frequency electric hearing should provide temporal envelope pitch from unresolved harmonics. How the acoustic and electric auditory inputs interact for H-CI users is largely unknown. Harmonicity and inharmonicity are emergent features of sound in which overtones are concordant or discordant with the fundamental frequency. We hypothesized that some H-CI users would be able to integrate acoustic and electric information for complex tone pitch perception, and that this ability would be correlated with speech-in-noise performance. In this study, we used perception of inharmonicity to demonstrate this integration. MethodsFifteen H-CI users with only acoustic hearing below 500 Hz, only electric hearing above 2 kHz, and more than 6 months CI experience, along with eighteen normal hearing (NH) controls, were presented with harmonic and inharmonic sounds. The stimulus was created with a low frequency component, corresponding with the H-CI user's acoustic hearing (fundamental frequency between 125 and 174 Hz), and a high frequency component, corresponding with electric hearing. Subjects were asked to identify the more inharmonic sound, which requires the perceptual integration of the low and high components. Speech-in-noise performance was tested in both groups using the California Consonant Test (CCT), and perception of Consonant-Nucleus-Consonant (CNC) words in quiet and AzBio sentences in noise were tested for the H-CI users. ResultsEight of the H-CI subjects (53%), and all of the NH subjects, scored significantly above chance level for at least one subset of the inharmonicity detection task. Inharmonicity detection ability, but not age or pure tone average, predicted speech scores in a linear model. These results were significantly correlated with speech scores in both quiet and noise for H-CI users, but not with speech in noise performance for NH listeners. Musical experience predicted inharmonicity detection ability, but did not predict speech performance. ConclusionsWe demonstrate integration of acoustic and electric information in H-CI users for complex pitch sensation. The correlation with speech scores in H-CI users might be associated with the ability to segregate a target speaker from background noise using the speaker's fundamental frequency.

Understanding pitch perception through physiological, modeling, and behavioural methods

Pitch is a salient perceptual quality that underlies our musical experience, interpretation of speech, and ability to attend to one of multiple speakers. Yet the brain mechanisms that support this key percept remain unclear. We have measured the pitch discrimination of humans, ferrets, and mice on a 2-alternative forced choice task. These experiments show that species differ in their weighting of harmonic and temporal envelope cues for pitch judgments. By applying existing computational models, we demonstrate how cochlear filter properties can explain some of these species differences. We have also used microelectrode recordings in behaving ferrets to understand how individual cortical neurons represent pitch. We find that: (1) cortical activity correlates better with ferrets’ pitch judgements than stimulus f0; and (2) inhibition can shape neural representations of f0 when animals are actively engaged in a pitch discrimination task, compared to when they are passively listening to the same sounds. We are now using 2-photon calcium imaging, during which we can measure the precise spatial position and responses of large numbers of individual neurons simultaneously, to better understand how and where pitch is extracted within the cortical microcircuit.

Time-scaling nonvibrato musical tones while preserving timbral texture

Sounds produced by linear stretching of nonvibrato single tones fail to preserve their original microvariations. While looping is commonly used for elongation with wavetable synthesis, this method requires careful attention to periodic waveform boundaries. Time extension by time reversal ensures continuity in the time domain, but this method causes audible clicks due to waveform phase reversals. This problem is overcome by using a pitch-synchronous phase vocoder method that generates time-varying harmonic amplitude and frequency envelopes. Applying the time-reversal looping method to these envelopes and converting to the time domain via sinusoidal additive synthesis can generate elongated versions of the original sound without audible clicks. To retain realism, original attack and decay time data are preserved. For shortening, envelopes are cross-faded between the attack-end and decay-begin points. As an application, the algorithm has been implemented in a score-processing music synthesis program.

Tissue Characterization on Ultrasound Harmonic Signals using Nakagami Statistics

Quantitative ultrasound (QUS) imaging provides a way to characterize biological tissue. The QUS estimates can be obtained from the envelope statistics. Previous studies are mainly based on the whole backscattered signals analysis. However, the ultrasound propagation is a nonlinear process and the harmonic signals can therefore reveal the nonlinear nature of a biological medium. The present study investigates the statistics of harmonic signal envelopes to relate the distribution parameters to the nonlinear coefficients. The main results demonstrate that the distributions exhibit a different behavior for fundamental and harmonic signals and that media with different nonlinearities can be distinguished, when using Nakagami statistics on the harmonic signal envelopes.

Harmonic Bandwidth Companding for Separation of Overlapping Harmonics in Pitched Signals

We present a novel approach to separating pitched signals from single-channel mixtures by harmonic bandwidth companding. Recalling that in a short analysis window the harmonic waveform envelope conveys information about approximate amplitude and frequency time variations, we show that proper linear waveform envelope smoothing reduces frequency spread around the harmonics and thus compresses the harmonic bandwidth. Such an action largely relaxes worst-case separation scenarios, which are caused by large proportions of overlapped harmonics. The distortion in separated signals due to harmonic bandwidth compression is compensated by an inverse system—the harmonic bandwidth expander. The benefit of such an approach is that explicit classification in overlapped and non-overlapped harmonics is no longer needed. Moreover, the underlying signal model is linear-in-parameters which allows for an efficient estimation via linear least-squares. The results show that harmonic bandwidth companding significantly outperforms two state-of-the-art separation methods.

A closed‐form equation approach to multi‐port/multi‐zone behavioral modeling of GaN FET Amplifiers

SummaryIn this paper, a systematic method for the simulation of weakly and mildly nonlinear GaN FET amplifiers is reported. The core of the proposal is a third‐order Volterra‐based behavioral model with multi‐spectral and multi‐node capabilities that is formally derived from a circuit‐level representation. Starting with the equivalent circuit of a typical FET device with thermal power feedback and fading memory, described in terms of its large‐signal functions, closed‐form expressions for the kernels at the gate, drain and thermal nodes are developed up to the third order. The use of these kernels allows the calculation of the responses in the dc, first‐, second‐ and third‐harmonic zones, which are shown to be dependent on the frequency response of the amplifier circuit terminating impedances and thermal filter. The simulation approach has been applied to calculate the nonlinear response of a typical power amplifier circuit, showing the ability of the proposed approach to provide an accurate prediction of multi‐spectral, multi‐node, multi‐bias characteristics, including AM/AM‐AM/PM conversion, spectral regrowth, intermodulation, and temperature rise, under diverse input signal waveforms and bandwidths. These results have been successfully compared with commercial CAD tools based on harmonic balance or envelope simulation. Copyright © 2014 John Wiley & Sons, Ltd.

A Volterra-Based Procedure for Multi-Port and Multi-Zone GaN FET Amplifier CAD Simulation

This paper reports a systematic method for the computer-aided-design (CAD) simulation of GaN FET power amplifiers (PAs). The core of the proposal is a Volterra-based behavioral model (BM) with multi-spectral and multi-node capabilities, which black-box structure is formally derived from a circuit-level representation of the PA and accounts for both short and long-term memory effects. Starting with the equivalent circuit of a typical FET device with thermal power feedback, the structures of the kernels for the gate, drain and thermal nodes are developed and are shown to be dependent on the frequency response of the PA terminating impedances and thermal filter. The model has been applied to simulate the nonlinear response of a typical PA circuit, showing the ability of the proposed model to provide an accurate prediction of multi-spectral, multi-node characteristics, including AM/AM-AM/PM conversion, spectral regrowth, intermodulation, and temperature rise, under diverse input signal waveforms and bandwidths. These results have been successfully compared with commercial CAD tools based on harmonic balance or envelope simulation.

Spalling Size Evaluation of Rolling Element Bearing Using Acoustic Emission

Spalling of the races or rolling elements is one of the most common faults in rolling element bearings. Exact estimation of the spall size is helpful to the life prediction for rolling element bearings. In this paper, the dual-impulsive phenomenon in the response of a spalled rolling element bearing is investigated experimentally, where the acoustic emission signals are utilized. A new method is proposed to estimate the spall size by extracting the envelope of harmonics of the ball passing frequency on the outer race from the squared envelope spectrum. Compared with the cepstrum analysis, the proposed procedure shows more powerful anti-noise ability in the fault size evaluation.

Dispersive terms in the averaged Lagrangian method

In this paper we develop Whitham's formalism of the averaged Lagrangian in the problem of Stokes waves on the surface of a layer of ideal fluid by taking into account dispersive terms. We derive a general expression for the Lagrangian in which Whitham's term with the non-linear frequency of narrow-band wave trains is expressed in explicit form using derivatives of the complex amplitude phase of the first harmonic envelope. This Lagrangian form simplifies derivation of the evolution equations as variational equations.

Chirp-encoded excitation for dual-frequency ultrasound tissue harmonic imaging

Dual-frequency (DF) transmit waveforms comprise signals at two different frequencies. With a DF transmit waveform operating at both fundamental frequency (f(0)) and second-harmonic frequency (2f(0)), tissue harmonic imaging can be simultaneously performed using not only the conventional 2f(0) second-harmonic signal but also using the f(0 )frequency-difference harmonic signal. Nonetheless, when chirp excitation is incorporated into the DF transmit waveform for harmonic SNR improvement, a particular waveform design is required to maintain the bandwidth of the f(0) harmonic signal. In this study, two different DF chirp waveforms are proposed to produce equal harmonic bandwidth at both the f(0) and 2f(0) frequencies to achieve speckle reduction by harmonic spectral compounding and to increase harmonic SNR for enhanced penetration and sensitivity. The UU13 waveform comprises an up-sweeping f(0) chirp and an up-sweeping 2f(0) chirp with triple bandwidth, whereas the UD11 waveform includes an up-sweeping f(0) chirp and a down-sweeping 2f(0) chirp with equal bandwidth. Experimental results indicate that the UU13 tends to suffer from a high range side lobe level resulting from 3f(0) interference. Consequently, the 2f(0) harmonic envelopes of the UD11 and the UU13 waveforms have compression qualities of 87% and 77%, respectively, when the signal bandwidth is 30%. When the bandwidth increases to 50%, the compression quality of the 2f(0) harmonic envelope degrades to 78% and 54%, respectively, for the UD11 and the UU13 waveforms. The compression quality value of the f0 harmonic envelope remains similar between the two DF transmit waveforms for all signal bandwidths. B-mode harmonic images also show that the UD11 is less contaminated by range side lobe artifacts than is the UU13. Compared with a short pulse with equal bandwidth, the UD11 waveform not only preserves the same spatial resolution after compression but also improves the image SNR by about 10 dB. Moreover, the image contrast-to-noise ratio (CNR), defined as the ratio of the mean to the standard deviation of image intensity in the speckle region, can be increased from 1.0 to about 1.2 when DF spectral compounding is performed. Therefore, it is concluded that the UD11 waveform is a potential solution for chirp-encoded DF harmonic imaging.