Amplitude Frequency Modulation Research Articles

The human auditory system uses amplitude modulation to distinguish music from speech.

Music and speech are complex and distinct auditory signals that are both foundational to the human experience. The mechanisms underpinning each domain are widely investigated. However, what perceptual mechanism transforms a sound into music or speech and how basic acoustic information is required to distinguish between them remain open questions. Here, we hypothesized that a sound's amplitude modulation (AM), an essential temporal acoustic feature driving the auditory system across processing levels, is critical for distinguishing music and speech. Specifically, in contrast to paradigms using naturalistic acoustic signals (that can be challenging to interpret), we used a noise-probing approach to untangle the auditory mechanism: If AM rate and regularity are critical for perceptually distinguishing music and speech, judging artificially noise-synthesized ambiguous audio signals should align with their AM parameters. Across 4 experiments (N = 335), signals with a higher peak AM frequency tend to be judged as speech, lower as music. Interestingly, this principle is consistently used by all listeners for speech judgments, but only by musically sophisticated listeners for music. In addition, signals with more regular AM are judged as music over speech, and this feature is more critical for music judgment, regardless of musical sophistication. The data suggest that the auditory system can rely on a low-level acoustic property as basic as AM to distinguish music from speech, a simple principle that provokes both neurophysiological and evolutionary experiments and speculations.

A new triple voltage gain seven level switched capacitor-based inverter with minimum voltage stress

Abstract This paper presents, a new seven level triple voltage gain inverter topology is proposed based on switched capacitor technique. The proposed inverter topology has minimum voltage stresses on the switches and balanced capacitor voltages. This paper briefs the operation of proposed topology, voltage stress analysis, capacitor sizing and generation gate signals for the switches. In addition, proposed topology is modeled in industrial based software PLECS with practical switches to study thermal behavior and efficiency analysis. Further, the proposed inverter topology is compared with competitive topologies in the recent literature. The proposed topology has merits like minimum total standing voltage, switching redundancy and inherent polarity generation. Furthermore, MATLAB based simulations and experimental analysis is done to validate the superior performance the proposed topology. The experimental results for the proposed seven-level inverter are presented and discussed in brief by considering different types of loads, amplitude modulation variations and frequency variations.

Analysis of Amplitude Modulation of EEG Based on Holo-Hilbert Spectrum Analysis During General Anesthesia.

The study aims to investigate the relationship between amplitude modulation (AM) of EEG and anesthesia depth during general anesthesia. In this study, Holo-Hilbert spectrum analysis (HHSA) was used to decompose the multichannel EEG signals of 15 patients to obtain the spatial distribution of AM in the brain. Subsequently, HHSA was applied to the prefrontal EEG (Fp1) obtained during general anesthesia surgery in 15 and 34 patients, and the α-θ and α-δ regions of feature (ROFs) were defined in Holo-Hilbert spectrum (HHS) and three features were derived to quantify AM in ROFs. During anesthetized phase, an anteriorization of the spatial distribution of AMs of α-carrier in brain was observed, as well as AMs of α-θ and α-δ in the EEG of Fp1. The total power ([Formula: see text]), mean carrier frequency ([Formula: see text]) and mean amplitude frequency ([Formula: see text]) of AMs changed during different anesthesia states. HHSA can effectively analyze the cross-frequency coupling of EEG during anesthesia and the AM features may be applied to anesthesia monitoring. The study provides a new perspective for the characterization of brain states during general anesthesia, which is of great significance for exploring new features of anesthesia monitoring.

Psychoacoustic and electroencephalographic responses to changes in amplitude modulation depth and frequency in relation to speech recognition in cochlear implantees

Temporal envelope modulations (TEMs) are one of the most important features that cochlear implant (CI) users rely on to understand speech. Electroencephalographic assessment of TEM encoding could help clinicians to predict speech recognition more objectively, even in patients unable to provide active feedback. The acoustic change complex (ACC) and the auditory steady-state response (ASSR) evoked by low-frequency amplitude-modulated pulse trains can be used to assess TEM encoding with electrical stimulation of individual CI electrodes. In this study, we focused on amplitude modulation detection (AMD) and amplitude modulation frequency discrimination (AMFD) with stimulation of a basal versus an apical electrode. In twelve adult CI users, we (a) assessed behavioral AMFD thresholds and (b) recorded cortical auditory evoked potentials (CAEPs), AMD-ACC, AMFD-ACC, and ASSR in a combined 3-stimulus paradigm. We found that the electrophysiological responses were significantly higher for apical than for basal stimulation. Peak amplitudes of AMFD-ACC were small and (therefore) did not correlate with speech-in-noise recognition. We found significant correlations between speech-in-noise recognition and (a) behavioral AMFD thresholds and (b) AMD-ACC peak amplitudes. AMD and AMFD hold potential to develop a clinically applicable tool for assessing TEM encoding to predict speech recognition in CI users.

Disentangling the effects of hearing loss and age on amplitude modulation frequency selectivity.

The processing and perception of amplitude modulation (AM) in the auditory system reflect a frequency-selective process, often described as a modulation filterbank. Previous studies on perceptual AM masking reported similar results for older listeners with hearing impairment (HI listeners) and young listeners with normal hearing (NH listeners), suggesting no effects of age or hearing loss on AM frequency selectivity. However, recent evidence has shown that age, independently of hearing loss, adversely affects AM frequency selectivity. Hence, this study aimed to disentangle the effects of hearing loss and age. A simultaneous AM masking paradigm was employed, using a sinusoidal carrier at 2.8 kHz, narrowband noise modulation maskers, and target modulation frequencies of 4, 16, 64, and 128 Hz. The results obtained from young (n = 3, 24-30 years of age) and older (n = 10, 63-77 years of age) HI listeners were compared to previously obtained data from young and older NH listeners. Notably, the HI listeners generally exhibited lower (unmasked) AM detection thresholds and greater AM frequency selectivity than their NH counterparts in both age groups. Overall, the results suggest that age negatively affects AM frequency selectivity for both NH and HI listeners, whereas hearing loss improves AM detection and AM selectivity, likely due to the loss of peripheral compression.

THz-wave multilevel frequency modulation by a single wavelength-tunable laser

Photomixing is one of the promising THz-wave generation methods. A conventional photomixing system with two lasers results in increasing the volume and power consumption of the system. For downsizing the system and reducing its power consumption, we have previously proposed a method to generate a THz-wave by a single wavelength-tunable laser. This technique can generate a quasi-continuous THz wave as well as a pulsed THz wave, based on which we are studying toward pulse frequency-amplitude modulation as a multi-level modulation method. In this paper, we have successfully generated a THz wave with frequency modulation between 286 GHz and 322 GHz by a single wavelength-tunable laser.

HE EFFICIENT PERFORMANCE OF GENERALIZED SELECTIVE COMBINING TECHNIQUES ON RAYLEIGH FADING CHANNEL USING HYBRIDIZED MODULATION SCHEME

This study concentrated on improving Generalized Selective Combining (GSC), one of the widely used diversity combining methods in telecommunications, by combining the modulation schemes of Quadrature Amplitude Modulation (QAM) and Orthogonal Frequency Division Multiplexing (OFDM) over a Rayleigh Fading channel. These were done with the intention of delivering strong Quality of Service (QoS) in mobile communication, particularly with the goal of lowering Bit Error Rate (BER) to improve reception on the receiving end. According to the findings, the communication system’s performance efficiency was increased through the hybridization of the modulation schemes, with QAM (4 and 16 constellation being taken into consideration for this research) and OFDM, even though a Rayleigh Fading channel was used, preventing line of sight (LOS). Compared to the BER values obtained when the modulation schemes were not hybridized, GSC was considerably improved with a low BER. In light of the fact that the channel under consideration did not experience severe fading, which is what caused the low BER observed, this article indicates that GSC might be improved through the hybridization of modulation schemes to provide a good Quality of Services.

Separation of signal and harmonics in non-explosive seismic prospecting with amplitude and nonlinear frequency-modulated signals

When vibroseis oscillations are excited, along with the main signal, harmonics are generated. They travel into the Earth and, like the main signal, interact with the target reflectors. Harmonics have a wider than that of the main signal frequency band, so they can be used to increase the resolution of the seismic data. To do this, the signal-related data should be separated from the harmonic-related data. This problem can be successfully solved by the previously proposed optimization recursive filtering algorithm, which, however, was developed only for linearly frequency-modulated signals. In this work, the algorithm is generalized to the case of amplitude modulation and nonlinear frequency modulation. Examples of application of the technique to increase the resolution of real vibroseis data are given.

A Rydberg atom-based amplitude-modulated receiver using the dual-tone microwave field

We propose a Rydberg atom-based receiver for amplitude-modulation (AM) reception utilizing a dual-tone microwave field. The pseudo-random binary sequence (PRBS) signal is encoded in the basic microwave field (B-MW) at the frequency of 14.23 GHz. The signal can be decoded by the atomic receiver itself but more obvious with the introduction of an auxiliary microwave (A-MW) field. The receiver’s amplitude variations corresponding to microwave field are simulated by solving density matrices to give this mechanism theoretical support. An appropriate AM frequency is obtained by optimizing the signal-to-noise ratio, guaranteeing both large data transfer capacity (DTC) and high fidelity of the receiver. The power of two MW fields, along with the B-MW field frequency, is studied to acquire larger DTC and wider operating bandwidth. Finally, the readout of PRBS signals is performed by both the proposed and conventional mechanisms, and the comparison proves the obvious increment of DTC with the proposed scheme. This proof-of-principle demonstration exhibits the potential of the dual-tone scheme and offers a novel pathway for Rydberg atom-based microwave communication, which is beneficial for long-distance communication and weak signal perception outside the laboratory.

Laser Frequency Modulation and PM-to-AM Noise Conversion in Atomic Clocks.

Laser wavelength stability is a necessity in present-day chip-scale atomic clocks (CSACs), in next-generation atomic clocks planned for Global Navigation Satellite Systems (GNSSs), and in many other atomic devices that generate their signals with lasers. Routinely, this is accomplished by modulating the laser's frequency about an atomic or molecular resonance, which in turn induces modulated laser-light absorption. The modulated absorption then generates a correction signal that stabilizes the laser wavelength. However, in addition to creating absorption modulation for laser wavelength stabilization, the modulated laser frequency can produce a time-dependent variance in transmitted laser intensity noise because of laser phase-noise (PM) to transmitted laser intensity-noise (AM) conversion. Here, we show that the time-varying PM-to-AM conversion can have a significant influence on the short-term frequency stability of vapor-cell atomic clocks. If diode-laser enabled vapor-cell atomic clocks are to break into the [Formula: see text] frequency-stability range, the amplitude of laser frequency modulation for wavelength stabilization will need to be chosen judiciously.

Characterization of nanoscale morphology and mechanical properties of conjugated polymer thin films dynamically exposed to a secondary solvent

Solution processing techniques are often used to enhance intra and interchain order in semiconducting conjugated polymer thin films used in the active layer of organic optoelectronic devices. While there has been extensive research into the impact of solution processing on the local structural and electronic properties of these films, the nanomechanical properties of the films are less well understood and are challenging to characterize. We investigate the nanomechanical properties of conjugated polymer thin films arising from solution processing techniques. Our study relies on dynamic secondary solvent dripping to induce subtle changes to the film morphology. We examine thin films of P3HT, PCDTBT, PTB7, and PBDB-T-SF conjugated polymers, commonly used in organic photovoltaics, with the bimodal amplitude modulation-frequency modulation (AM-FM) imaging mode of the atomic force microscopy (AFM) viscoelastic method to probe their local physical and mechanical properties. We find that Young's Modulus data measured by AM-FM AFM can detect additional changes in film properties not discernible by other commonly used bulk thin-film characterization techniques. For PBDB-T-SF, we detect an increase in molecular order that is not noticable by UV–visible absorption spectroscopy, X-ray diffraction or nanoindentation. PCDTBT, the most amorphous of the polymers studied, shows no changes in absorption or X-ray diffraction data, yet clear changes in Young's Modulus were detected by AFM. On the other hand, increases in P3HT order that occurred due to dynamic secondary solvent dripping are detected in both the bulk and AFM measurements. Our study demonstrates the applicability of nanomechanical measurements for characterizing local structural variations in conjugated polymer films. This work is relevant to ongoing efforts to control and understand the complex structure-property-processing relationships of conjugated polymer thin films.

A dual-function tunable terahertz multiband bandpass filter based on PET woven-wire meshes with conductive coating surfaces

A multifunctional terahertz (THz) device with frequency tunability, amplitude modulation and spectral filtering abilities, and substrate flexibility is highly desired for various applications, such as THz communication, sensing, wearable optoelectronics. Therefore, this study proposed a 3D artificial material based on a flexible polyethylene terephthalate (PET) woven-wire mesh with conductive coating surfaces. This material was conceptually demonstrated in experiments as a dual-functional THz device. In addition, the transmission properties of this artificial material were experimentally and numerically explored with reasonable agreement. Then, the underlying mechanism of the spectral characteristics was qualitatively elucidated. The amplitudes and frequencies of the spectral characteristics were successfully validated to be passively manipulated by tailoring the structural parameters of a unit cell and changing the surface conductivities of a device. This process opened the application feasibility of a frequency tunable bandpass filter and a power switch at the THz regime. For the bandpass filter application, the tri-frequency modulation capability was experimentally demonstrated, and a frequency tuning bandwidth of 0.249 THz was achieved by varying the conductivity of the device’s surface-coating layer from 0.44 to 77 MS/m. For the power switch application, the largest modulation depth between the on and off states of a device was successfully demonstrated at approximately 21.3 dB at 0.271 THz. This dual-function THz device has the advantages of compactness, low cost, and easy fabrication, thus providing an alternative strategy to develop tunable, flexible, and versatile THz devices for broad applications.

Low-Frequency Discontinuous Noise Diagnosis and Reduction of Air Conditioner Outdoor Unit

Abnormal discontinuous low-frequency noise occurs in the outdoor unit when the air conditioner is operating at 86~96 Hz. This noise has the characteristics of low frequency, strong penetration, long transmission distance, and poor sound quality, which can cause serious noise pollution. In order to reduce the low-frequency noise of the outdoor unit of the air conditioner, the discontinuous noise frequency is first located by testing the time-domain and frequency-domain maps of the noise. It is then compared with the frequency of fan rotation noise and structural radiation noise. It is found that the discontinuous noise is caused by the coupling of fan rotation noise and structural radiation noise. It is found that low-frequency noise improvement is significant when the frequency difference between two noise peaks is greater than 8 Hz or when a single noise peak is less than 25 dB(A) by studying the methods of frequency modulation and amplitude modulation of noise peaks. By adjusting the fan speed from 930 rpm to 940 rpm, the problem of 94 Hz noise is solved. Then, through testing the natural frequencies of the pipe and shell, it is found that the natural frequencies of the pipe are close to the excitation frequencies. The structural radiation noise is mainly caused by the pipe. Modal analysis is conducted on the pipe. When the normal boundary with the condenser and the normal boundary with the valve of the pipe is constrained by springs, the simulated values are closer to the measured values. Finally, structural optimization design is carried out on the pipe. When the U-tube of the exhaust pipe is shortened by 30 mm, a 30 g mass block is added to the cold inlet pipe, and a 97 g mass block is added to the lower part of the valve pipe of the suction pipe. The discontinuous noise of the optimized prototype is significantly improved.

An adaptive VNCMD and its application for fault diagnosis of industrial sewing machines

Due to the non-linearity and non-stationarity of sound signals from complex transmission structure and frequent start-stop of industrial equipment, such as sewing machine, its incipient faults cannot be accurately identified with classical fault diagnosis methods. Therefore, a new fault diagnosis method with an adaptive variational nonlinear chirp mode decomposition (AVNCMD) is proposed. Firstly, a pre-processing step of convex optimization with generalized minimax-concave penalty function and spline-kernelled chirplet transform is applied to obtain the time–frequency distribution (TFD) with energy concentration, and a peak frequency extension method is proposed to adaptively search initial instantaneous frequencies of AVNCMD on the TFD; then the Pearson correlation coefficient is introduced as the termination condition of the adaptive signal decomposition. Secondly, multi-domain features are extracted from the decomposed nonlinear chirp modes, and an optimal features set is constructed by the feature preference method of an improved ReliefF. Finally, the fault classification is realized by the extreme learning machine, whose input weights and biases are optimized via the salp swarm algorithm. The AVNCMD is testified to be accurate in simulation with nonlinear amplitude modulation–frequency modulation signals and be effective in actual sound signals of industrial sewing machines on four different states. Through the detailed analysis of the measured sound signals in factory, the proposed fault diagnosis method can identify four states of the industrial sewing machines with an overall identification accuracy of 95.0%.

Clinical Standardization for the Detection of Hemispheric Dominance for Steady-State Auditory Evoked Fields (SSAEFs) in Normal Hearing.

Steady-state auditory evoked responses (SSAERs) are promising indicators of major auditory function. The improvement in accessibility in the clinical setting depends on the standardization and definition of the characteristics of SSAERs. There have been some insights into the changes in the interhemispheric dominance of SSAERs in some clinical entities. However, the hemispheric asymmetry of SSAERs in healthy controls remains inconclusive. Twelve right-handed healthy volunteers with normal hearing were recruited. Steady-state auditory evoked fields (SSAEFs) were measured binaurally using magnetoencephalography (MEG) under pure-tone auditory stimuli at 1000 Hz with an amplitude modulation frequency of 43 Hz. The laterality index, based on the ratio of SSAEF strength over the right hemisphere to that over the left hemisphere, was also analyzed. The SSAEFs source was localized bilaterally on the superior temporal plane, with an orientation centripetal to the auditory cortex. The laterality index ranged from 1.1 to 2.3, and there were no sex differences. In all subjects, the strength of the SSAEFs was significantly weaker in the left hemisphere than in the right hemisphere (p=0.014). Right-sided dominance of the SSAEFs was verified in subjects with normal hearing. Acoustic sources clinically available in audiometric tests were used as stimuli. Such a simplification of parameters would be helpful for the standardization of precise production and the definition of the characteristics of SSAERs. Since MEG is still not easily accessible clinically, further studies using electroencephalography with larger sample sizes are necessary to address these issues.

The impact of amplitude modulation frequency in harmonic motion imaging on inclusion characterization.

Ultrasound elasticity imaging techniques aim to provide a non-invasive characterization of tissue mechanical properties to detect pathological changes and monitor disease progression. Harmonic motion imaging (HMI) is an ultrasound-based elasticity imaging technique that utilizes an oscillatory acoustic radiation force to induce localized displacements and estimate relative tissue stiffness. Previous studies have applied a low amplitude modulation (AM) frequency of 25 or 50 Hz in HMI to assess the mechanical properties of different tissue types. In this study, we investigate the dependence of AM frequency in HMI and whether the frequency can be adjusted based on the size and mechanical properties of the underlying medium for enhanced image contrast and inclusion detection. A tissue-mimicking phantom with embedded inclusions at different sizes and stiffnesses was imaged within a range of AM frequencies from 25 to 250 Hz at 25-Hz step size. The AM frequency at which the maximum contrast and CNR are achieved depends on the size and stiffness of the inclusions. A general trend shows that contrast and CNR peak at higher frequencies for smaller inclusions. In addition, for some inclusions with the same size but different stiffnesses, the optimized AM frequency increases with the stiffness of the inclusion. Nevertheless, there is a shift between the frequencies at which the contrast peaks and those with maximum CNR. Finally, in agreement with the phantom findings, imaging an ex-vivo human specimen with a 2.7-cm breast tumor at a range of AM frequencies showed that the highest contrast and CNR are achieved at the AM frequency of 50 Hz. These findings indicate that the AM frequency can be optimized in different applications of HMI, especially in the clinic, for improved detection and characterization of tumors with different geometries and mechanical properties.

On the geometric phases during radio frequency pulses with sine and cosine amplitude and frequency modulation.

In this work, we describe the formation of geometric phases during nonadiabatic frequency swept (FS) radio frequency (RF) pulses with sine amplitude modulation and cosine frequency modulation functions. The geometric phases during the FS pulse were analyzed using a Schrödinger equation formalism, and the unified analytical expression for the geometric phase was derived. We present the solutions for sub-geometric phase components incorporated in spinor wavefunctions for the RF Hamiltonian of spin ½ nuclei. We demonstrate that the geometric phases during sine/cosine RF pulses are opposite in signs for different initial conditions of the spinor and that geometric phases can accumulate in correspondence to different magnetization trajectories. The derived formalism could be extended for the evaluation of the geometric phases during a wide class of amplitude- and frequency-modulated pulses used in MRI and in high-resolution NMR.

Low-energy amplitude-modulated electromagnetic field exposure: Feasibility study in patients with hepatocellular carcinoma.

Patients with advanced hepatocellular carcinoma (HCC) and poor liver function lack effective systemic therapies. Low-energy electromagnetic fields (EMFs) can influence cell biological processes via non-thermal effects and may represent a new treatment option. This single-site feasibility trial enrolled patients with advanced HCC, Child-Pugh A and B, Eastern Cooperative Oncology Group 0-2. Patients underwent 90-min amplitude-modulated EMF exposure procedures every 2-4 weeks, using the AutEMdev (Autem Therapeutics). Patients could also receive standard care. The primary endpoints were safety and the identification of hemodynamic variability patterns. Exploratory endpoints included health-related quality of life (HRQoL), overall survival (OS). and objective response rate (ORR) using RECIST v1.1. Sixty-six patients with advanced HCC received 539 AutEMdev procedures (median follow-up, 30 months). No serious adverse events occurred during procedures. Self-limiting grade 1 somnolence occurred in 78.7% of patients. Hemodynamic variability during EMF exposure was associated with specific amplitude-modulation frequencies. HRQoL was maintained or improved among patients remaining on treatment. Median OS was 11.3 months (95% confidence interval [CI]: 6.0, 16.6) overall (16.0 months [95% CI: 4.4, 27.6] and 12.0 months [6.4, 17.6] for combination therapy and monotherapy, respectively). ORR was 24.3% (32% and 17% for combination therapy and monotherapy, respectively). AutEMdev EMF exposure has an excellent safety profile in patients with advanced HCC. Hemodynamic alterations at personalized frequencies may represent a surrogate of anti-tumor efficacy. NCT01686412.

A Power System Reserve Configuration Solution That Satisfies the Frequency Stability Constraint Under the Given New Energy Index

Aiming at the problem of frequency stability and voltage stability of a new power system, this paper provides a new energy index method based on frequency stability constraints in the standby category of the new power system. Several concepts, such as maximum disturbance constraint and minimum reserve capacity, are proposed. Two constraints, power balance, and frequency constraint are set, and the factors to be considered, such as load frequency effect, security and control measure, demand-side response, and primary frequency change amplitude of each type of unit, are specified. Through analysis and study of regional data, the peak load of power grid new energy is a given index in a given scenario, according to the research of regional power grid in each category of a frequency modulation amplitude, the installed capacity is set to build a solution, to the problem of frequency stability caused by clean energy consumption, thus determine the ratio of each category of power output and heat capacity. Finally, according to the actual data of one regional power grid, the PSD-BPA power system simulation software is used to verify the effectiveness of the method.

Age-related reduction of amplitude modulation frequency selectivity.

The perception of amplitude modulations (AMs) has been characterized by a frequency-selective process in the temporal envelope domain and simulated in computational auditory processing and perception models using a modulation filterbank. Such AM frequency-selective processing has been argued to be critical for the perception of complex sounds, including speech. This study aimed at investigating the effects of age on behavioral AM frequency selectivity in young (n = 11, 22-29 years) versus older (n = 10, 57-77 years) listeners with normal hearing, using a simultaneous AM masking paradigm with a sinusoidal carrier (2.8 kHz), target modulation frequencies of 4, 16, 64, and 128 Hz, and narrowband-noise modulation maskers. A reduction of AM frequency selectivity by a factor of up to 2 was found in the older listeners. While the observed AM selectivity co-varied with the unmasked AM detection sensitivity, the age-related broadening of the masked threshold patterns remained stable even when AM sensitivity was similar across groups for an extended stimulus duration. The results from the present study might provide a valuable basis for further investigations exploring the effects of age and reduced AM frequency selectivity on complex sound perception as well as the interaction of age and hearing impairment on AM processing and perception.