Random Amplitude Modulation Research Articles

Development and application of a semantic differential for perception-based optimization of wind turbine and other broadband sounds

Growing numbers of the population are exposed to wind turbine (WT) and other broadband sound sources from the environment. Acoustically optimizing emissions of environmental noise sources to minimize negative effects on the population therefore becomes increasingly important. The objective of this study was to develop and apply a semantic differential (SD) for multidimensional perception-based assessment of WT and other broadband sounds, to be potentially applied for acoustic optimization. An SD was developed specifically for broadband sounds and applied in a laboratory listening experiment, using outdoor WT and other broadband sounds covering a wide spectral range, at 40 dBA playback level. Fifty-two participants rated the sounds using the SD. Relevant perceptual dimensions were extracted, and a prediction model for noise annoyance was established on this basis. The experiment revealed that participants could well describe and discriminate the sound characteristics using the affective-evaluative everyday language of the SD. Four perceptual dimensions (or factors) were identified: Evaluation, Timbre, Activity and Randomness, with the latter three describing spectral shape, periodic amplitude modulation and random amplitude modulation, respectively. The factors were strongly linked with annoyance and well suited to establish an annoyance prediction model. The results can be applied in a perception-influenced design to identify how to optimize (perceived) acoustical characteristics and thus minimize annoyance effects on the population. Also, they might potentially be used in field surveys for a multidimensional assessment of broadband sounds to study the long-term annoyance potential of specific perceptual characteristics. This might eventually help to refine exposure–response relationships using predictors beyond basic noise metrics.

Performance Enhancement of a Spin-Wave-Based Reservoir Computing System Utilizing Different Physical Conditions

We numerically study how to enhance reservoir computing performance by thoroughly extracting the spin-wave device potential for higher-dimensional information generation. The reservoir device has a 1-input exciter and 120-output detectors on the top of a continuous magnetic garnet film for spin-wave transmission. For various nonlinear and fading-memory dynamic phenomena distributing in the film space, small in-plane magnetic fields are used to prepare stripe domain structures and various damping constants at the film sides and bottom are explored. The ferromagnetic resonant frequency and relaxation time of spin precession clearly characterizes the change in spin dynamics with the magnetic field and damping constant. The common input signal for reservoir computing is a 1-GHz cosine wave with random 6-valued amplitude modulation. A basic 120-dimensional reservoir output vector is obtained from time-series signals at the 120-output detectors under each of three magnetic field conditions. Then, 240- and 360-dimensional reservoir output vectors are also constructed by concatenating two and three basic ones, respectively. In nonlinear autoregressive moving average (NARMA) prediction tasks, the computational performance is enhanced as the dimension of the reservoir output vector becomes higher and a significantly low prediction error is achieved for the tenth-order NARMA task using the 360-dimensional vector and optimum damping constant. The results are clear evidence that the collection of diverse output signals efficiently increases the dimensionality of the integrated reservoir state vector (i.e. reservoir-state richness) and thereby contributes to high computational performance. This paper demonstrates that performance enhancement through various configuration settings is a practical approach for on-chip reservoir computing devices with small numbers of real output nodes.

Phase retrieval by random binary amplitude modulation and ptychography principle.

An improved binary amplitude modulation-based phase retrieval method studied by means of simulations and experiments is presented in this paper. The idea of ptychography is introduced for the purpose of designing random binary amplitude masks. The masks have the features that part of the light transmission regions is overlapped with each other and the overlapping positions are randomly distributed. The requirement for the consistency of light field in overlapping regions forms a strong constraint which is similar to the overlap constraint in ptychography. The constraint makes the iterative algorithm have high convergence accuracy in comparison to that of the original binary amplitude modulation method. Influences of amounts and overlap ratio of the modulation mask on reconstruction accuracy and speed of imaging process are analyzed. The comparison between our method and the original binary amplitude modulation method is performed in order to verify the feasibility of the proposed method.

Experimental optical encryption based on random mask encoding and deep learning

We present an experimental scheme for optical encryption using random mask encoding and deep learning technique. A phase image is encrypted into a speckle pattern by a random amplitude modulation in the optical transmission. Before decryption processing, a neural network model is used to learn the mapping relationship between the pure-phase object and the speckle image rather than characterizing the filter film used in the scheme explicitly or parametrically. The random binary mask is made by a polyethylene terephthalate film and 2500 object-speckle pairs are used for training. The experimental results demonstrate that the proposed scheme based on deep learning could be successfully used as a random binary mask encrypted image processor, which can quickly output the primary image with high quality from the cyphertext.

Time-Frequency Characteristics of Fluctuating Pressure on the Bottom of the Stilling Basin with Step-Down Floor Based on Hilbert–Huang Transform

Fluctuating pressure is an important feature of the bottom of a stilling basin with step-down floor. To analyze the frequency domain characteristics and energy distribution of this fluctuating pressure, the Hilbert–Huang transform (HHT) method is used. First, empirical mode decomposition is performed on the pressure fluctuation signal to obtain a number of intrinsic mode functions (IMFs), and then the Hilbert transformation is performed on each IMF to obtain the Hilbert spectrum and marginal spectrum for characterizing the pressure fluctuation signal. The results show that the fluctuating pressure signal of the stilling basin with step-down floor has obvious characteristics of low frequency and large amplitude. The dominant frequencies of the head and tail of the stilling basin are very prominent, and most of the energy is concentrated below 5.0 Hz; with the increase in the relative position of the measuring point, the energy distribution in stilling basin with step-down floor changes from high-frequency component to low-frequency component. The fluctuating pressure signal of the stilling basin with step-down floor has random amplitude modulation and frequency modulation. The marginal spectrum obtained by the HHT method can obtain the local characteristics of the signal more accurately and is more suitable for processing nonlinear and nonstationary signals.

Synthetic Aperture Radar Target Feature Modulation Using Active Frequency Selective Surface

Target feature control on the synthetic aperture radar (SAR) image using the passive way is a challenging task in the field of SAR jamming. The conventional passive jamming devices such as corner reflectors and chaffs cannot achieve the flexible modulation of SAR target feature duo to their fixed scattering cross section. As a passive material, active frequency selective surface (AFSS) can dynamically control their electromagnetic characteristics and has been widely applied in the radar target stealth field. In this paper, a target feature modulation method based on AFSS is proposed against SAR. The method intermittently switches the scattering intensity of AFSS material and imposes periodic or random code amplitude modulation onto the radar signal. As a consequence, multi-false targets with verisimilar characteristics or cross-shaped areas are formed when modulated signal is received and processed by the victim SAR. Thus, the protected target is difficult to detect and identify by the SAR system. Microwave anechoic chamber experiments and measured SAR data simulations with different modulating parameters are separately conducted to demonstrate the effectiveness of the proposed method.

Evolution of intense narrowband noise beams

The main part of this work is focused on the experimental study of the evolution of acoustic beams with a narrowband spectrum at the input. The nonlinear interaction leads to initiation of new harmonics whose width increases with the harmonic number and a continuous power spectrum is formed at high frequencies. The experimental equipment enables us to study the beam propagation at large acoustic Reynolds numbers and analyze the spectral content of the field in a wide frequency band. For narrowband noise, the input field can be considered as a quasi-monochromatic signal with random amplitude and phase modulation. The amplitude-modulation suppression is observed for large Reynolds numbers as the wave propagates. Far from the sound transducer, the field on the sound transducer axis is a sequence of discontinuities with a universal behaviour between them. The locations of the discontinuities and their amplitudes and, hence, the statistical characteristics of the waves are determined by the phase fluctuations of the initial wave. It has been theoretically shown that the field spectrum at the discontinuous stage has a universal structure which is determined by the probability distribution of the initial wave frequency. It has been demonstrated experimentally that the theory describes sufficiently well the noise-signal spectrum form at the discontinuous stage.

Cochlear hearing loss and the detection of sinusoidal versus random amplitude modulation.

This study assessed the effect of cochlear hearing loss on detection of random and sinusoidal amplitude modulation. Listeners with hearing loss and normal-hearing listeners (eight per group) generated temporal modulation transfer functions (TMTFs) for envelope fluctuations carried by a 2000-Hz pure tone. TMTFs for the two groups were similar at low modulation rates but diverged at higher rates presumably because of differences in frequency selectivity. For both groups, detection of random modulation was poorer than for sinusoidal modulation at lower rates but the reverse occurred at higher rates. No evidence was found that cochlear hearing loss, per se, affects modulation detection.

Cochlear hearing loss and the detection of sinusoidal versus random amplitude modulation

Cochlear hearing loss and the detection of sinusoidal versus random amplitude modulation

Collective effects due to dipolar fields as the origin of the extremely random behavior in hyperpolarized NMR maser: A theoretical and numerical study

Numerical simulations based on microscopic approach are used to explore the spin dynamics encountered in the recently reported hyperpolarized (129)Xe NMR maser [D. J. Y. Marion, G. Huber, P. Berthault, and H. Desvaux, ChemPhysChem 9, 1395-1401 (2008)] where series of amplitude modulated rf emissions are observed. The integration of the dynamic features of the electronic detection circuit in the present simulations, based on non-linear Maxwell-Bloch differential equations with dipole-dipole interactions, allows us to prove that the experimentally observed extremely random amplitude modulations crucially require the long-distance dipolar couplings between the nuclear spins with the feedback field acting as an amplifier. The massive dipolar couplings act, when the magnetization is largely tilted off the longitudinal axis, as an apparent transverse self-relaxation mechanism which destroys coherence. This, in particular, explains why the final magnetization after emissions can still be opposite to the magnetic field direction, i.e., being in an unstable state.

Suprathreshold Auditory Processing and Speech Perception in Noise: Hearing-Impaired and Normal-Hearing Listeners

It is widely believed that suprathreshold distortions in auditory processing contribute to the speech recognition deficits experienced by hearing-impaired (HI) listeners in noise. Damage to outer hair cells and attendant reductions in peripheral compression and frequency selectivity may contribute to these deficits. In addition, reduced access to temporal fine structure (TFS) information in the speech waveform may play a role. To examine how measures of peripheral compression, frequency selectivity, and TFS sensitivity relate to speech recognition performance by HI listeners. To determine whether distortions in processing reflected by these psychoacoustic measures are more closely associated with speech deficits in steady-state or modulated noise. Normal-hearing (NH) and HI listeners were tested on tasks examining frequency selectivity (notched-noise task), peripheral compression (temporal masking curve task), and sensitivity to TFS information (frequency modulation [FM] detection task) in the presence of random amplitude modulation. Performance was tested at 500, 1000, 2000, and 4000 Hz at several presentation levels. The same listeners were tested on sentence recognition in steady-state and modulated noise at several signal-to-noise ratios. Ten NH and 18 HI listeners were tested. NH listeners ranged in age from 36 to 80 yr (M = 57.6). For HI listeners, ages ranged from 58 to 87 yr (M = 71.8). Scores on the FM detection task at 1 and 2 kHz were significantly correlated with speech scores in both noise conditions. Frequency selectivity and compression measures were not as clearly associated with speech performance. Speech Intelligibility Index (SII) analyses indicated only small differences in speech audibility across subjects for each signal-to-noise ratio (SNR) condition that would predict differences in speech scores no greater than 10% at a given SNR. Actual speech scores varied by as much as 80% across subjects. The results suggest that distorted processing of audible speech cues was a primary factor accounting for differences in speech scores across subjects and that reduced ability to use TFS cues may be an important component of this distortion. The influence of TFS cues on speech scores was comparable in steady-state and modulated noise. Speech recognition was not related to audibility, represented by the SII, once high-frequency sensitivity differences across subjects (beginning at 5 kHz) were removed statistically. This might indicate that high-frequency hearing loss is associated with distortions in processing in lower-frequency regions.

Stochastic amplitude-modulated stretching of rabbit flexor digitorum profundus tendons reduces stiffness compared to cyclic loading but does not affect tenocyte metabolism

BackgroundIt has been demonstrated that frequency modulation of loading influences cellular response and metabolism in 3D tissues such as cartilage, bone and intervertebral disc. However, the mechano-sensitivity of cells in linear tissues such as tendons or ligaments might be more sensitive to changes in strain amplitude than frequency. Here, we hypothesized that tenocytes in situ are mechano-responsive to random amplitude modulation of strain.MethodsWe compared stochastic amplitude-modulated versus sinusoidal cyclic stretching. Rabbit tendon were kept in tissue-culture medium for twelve days and were loaded for 1h/day for six of the total twelve culture days. The tendons were randomly subjected to one of three different loading regimes: i) stochastic (2 – 7% random strain amplitudes), ii) cyclic_RMS (2–4.42% strain) and iii) cyclic_high (2 - 7% strain), all at 1 Hz and for 3,600 cycles, and one unloaded control.ResultsAt the end of the culture period, the stiffness of the “stochastic” group was significantly lower than that of the cyclic_RMS and cyclic_high groups (both, p < 0.0001). Gene expression of eleven anabolic, catabolic and inflammatory genes revealed no significant differences between the loading groups.ConclusionsWe conclude that, despite an equivalent metabolic response, stochastically stretched tendons suffer most likely from increased mechanical microdamage, relative to cyclically loaded ones, which is relevant for tendon regeneration therapies in clinical practice.

The role of time and place cues in the detection of frequency modulation by hearing-impaired listeners

Frequency modulation detection limens (FMDLs) were measured for five hearing-impaired (HI) subjects for carrier frequencies f(c) = 1000, 4000, and 6000 Hz, using modulation frequencies f(m) = 2 and 10 Hz and levels of 20 dB sensation level and 90 dB SPL. FMDLs were smaller for f(m) = 10 than for f(m) = 2 Hz for the two higher f(c), but not for f(c) = 1000 Hz. FMDLs were also determined with additional random amplitude modulation (AM), to disrupt excitation-pattern cues. The disruptive effect was larger for f(m) = 10 than for f(m) = 2 Hz. The smallest disruption occurred for f(m) = 2 Hz and f(c) = 1000 Hz. AM detection thresholds for normal-hearing and HI subjects were measured for the same f(c) and f(m) values. Performance was better for the HI subjects for both f(m). AM detection was much better for f(m) = 10 than for f(m) = 2 Hz. Additional tests showed that most HI subjects could discriminate temporal fine structure (TFS) at 800 Hz. The results are consistent with the idea that, for f(m) = 2 Hz and f(c) = 1000 Hz, frequency modulation (FM) detection was partly based on the use of TFS information. For higher carrier frequencies and for all carrier frequencies with f(m) = 10 Hz, FM detection was probably based on place cues.

Mechanisms underlying the detection of frequency modulation

Frequency modulation detection limens (FMDLs) were measured for carrier frequencies (f(c)) of 1000, 4000, and 6000 Hz, using modulation frequencies (f(m)) of 2 and 10 Hz and levels of 20 and 60 dB sensation level (SL), both with and without random amplitude modulation (AM), applied in all intervals of a forced-choice trial. The AM was intended to disrupt excitation-pattern cues. At 60 dB SL, the deleterious effect of the AM was smaller for f(m) = 2 than for f(m) = 10 Hz for f(c) = 1000 and 4000 Hz, respectively, while for f(c) = 6000 Hz the deleterious effect was large and similar for the two values of f(m). This is consistent with the idea that, for f(c) below about 5000 Hz and f(m) = 2 Hz, frequency modulation can be detected via changes in phase locking over time. However, at 20 dB SL, the deleterious effect of the added AM for f(c) = 1000 and 4000 Hz was similar for the two values of f(m), while for f(c) = 6000 Hz, the deleterious effect of the AM was greater for f(m) = 10 than for f(m) = 2 Hz. It is suggested that, at low SLs, the auditory filters become relatively sharp and phase locking weakens, so that excitation-pattern cues influence FMDLs even for low f(c) and low f(m).

FM-AM Conversion Induced by Polarization Mode Dispersion in Fiber Systems

The conversion of the frequency modulated pulse induced from frequency modulation (FM) to amplitude modulation (AM) by the polarization mode dispersion (PMD) is theoretically and experimentally investigated. When there is no polarizer at the output end of a fiber system, the amplitude modulation depth is stable by 8%. Random amplitude modulation is observed when a polarizer is placed at the output end of the fiber system. The observed minimum and maximum modulation depths in our experiment are 5% and 80%, respectively. Simulation results show that the amplitude modulation is stable by 4% induced mainly by group velocity dispersion (GVD) when there is no polarizer, and the amplitude modulation depth displays the random variation character induced by the GVD and PMD. Lastly, a new fiber system scheme is proposed and little amplitude modulation is observed at the top of the output pulse.

Neural Heterogeneities and the coding of contrast envelopes

It is well known that higher order neurons respond to contrast envelopes (second order statistics) present in sensory stimuli. These contrast envelopes can be defined as the curve connecting successive peaks in the stimulus and can only be obtained through a nonlinear transformation of the stimulus such as the Hilbert transform. They contain important information that is decoded by the brain: for example, removal of these envelopes from speech severely reduces its intelligibility. While recent studies have shown potential mechanisms by which higher order neurons can acquire sensitivity to contrast envelopes, it is generally thought that peripheral sensory neurons do not respond to them. Using the electrosensory system of the weakly electric fish as a model we performed extracellular recordings from primary afferents while presenting contrast-modulated random amplitude modulations (AMs) of the fish’s quasi-sinusoidal electric field and found that about 45% of units responded to the time varying contrast envelope. Previous studies have shown that these afferents are spontaneously active and display large heterogeneities in their firing rates and burst firing properties: we therefore investigated whether these heterogeneities are linked to contrast envelope coding. We found that afferents with low spontaneous firing rate responded best to the contrast envelope due to higher levels of rectification. We next investigated the basis of this higher level of rectification using a simple phenomenological model of primary afferent activity. We found that varying levels of intrinsic noise as well as overall bias current in our model could reproduce our experimental results, suggesting that neural heterogeneities can significantly influence contrast envelope coding at the sensory periphery.

Suprathreshold auditory processing and speech recognition in noise for hearing-impaired listeners.

Suprathreshold distortions in auditory processing contribute to speech recognition deficits for hearing-impaired (HI) listeners in noise. Outer hair cell damage and attendant reductions in frequency selectivity and peripheral compression may contribute to these deficits. Reduced sensitivity to spectral or temporal modulations or temporal fine structure (TFS) information may also play a role. Eight normal-hearing and 18 HI listeners were tested in psychoacoustic tasks to assess frequency selectivity (notched-noise), peripheral compression (temporal masking curves), TFS sensitivity [frequency modulation (FM) detection in the presence of random amplitude modulation], and spectrotemporal modulation (STM) sensitivity (spectral-temporal “ripple” detection). Performance was examined at 500, 1000, 2000, and 4000 Hz at several presentation levels. Listeners were also tested on sentence recognition in stationary and modulated noise (92-dB sound pressure level signal level; −6-, −3-, 0-, and +3-dB SNRs). HI listeners with similar audiometric thresholds showed a wide range of speech scores. Estimates of FM and STM sensitivity at 500 and 1000 Hz were significantly correlated with speech scores and with each other. Frequency selectivity and compression measures were not clearly associated with speech performance. Implications for models of HI speech intelligibility are discussed. [Work supported by the Oticon Foundation.]

Asymptotics of surface waves over random bathymetry

This paper addresses the propagation of free surface water waves over a variable seabed in the long wavelength scaling regime. We consider the situation in which the bathymetry is given by a stationary random process which has a correlation length substantially shorter than the wavelength of the principal surface wave components. An asymptotic description shows that the water waves problem is modeled by an effective system of equations that is related to the KdV, however in a reference frame given in terms of random characteristic coordinates, and in addition with a random amplitude modulation and random scattered component. The resulting random processes are strongly correlated and have canonical limits due to the Donsker invariance principle. Our analysis is based on the Hamiltonian description of water waves and long wave perturbation theory and a new criterion for asymptotic expansions of partial differential equations with rapidly varying coefficients. In this paper we give a detailed analysis of the transformation to random characteristic coordinates and the asymptotic form of the resulting transformed partial differential equations. A companion paper (de Bouard, A., Craig, W., Diaz-Espinosa, O., Guyenne, P., Sulem, C., Long wave expansions for water waves over random topography, Nonlinearity 21 (2008), 2143-2178) analyses in detail the asymptotic behavior of the resulting expression for solutions, and their consistency with the derivation of the effective model equations.

Limits of Linear Rate Coding of Dynamic Stimuli by Electroreceptor Afferents

We estimated the frequency-intensity (f-I) curves of P-unit electroreceptors using 4-Hz random amplitude modulations (RAMs) and using the covariance method (50-Hz RAMs). Both methods showed that P units are linear encoders of stimulus amplitude with additive noise; the gain of the f-I curve was, on average, 0.32 and 2.38 spikesxs(-1)xmicroV(-1) for the low- and high-frequency cutoffs, respectively. There were two sources of apparent noise in the encoding process: the first was the variability of baseline P-unit discharge and the second was the variation of receptor discharge due to variability of the stimulus slope independent of its intensity. The covariance method showed that a linear combination of eigenvectors representing the time-weighted stimulus intensity (E1) and its derivative (E2) could account for, on average, 92% of the total response variability; E1 by itself accounted for 76% of the variability. The low gain of the low-frequency f-I curve implies that detection of small (1 microV) signals would require integration over many receptors ( approximately 1,200) and time (200 ms); even then, signals that elicit behavioral responses could not be detected using rate coding with the estimated gain and noise levels. Weak signals at the limit of behavioral thresholds could be detected if the animal were able to extract E1 from the population of responding P units; we propose a tentative mechanism for this operation although there is no evidence as to whether it is actually implemented in the nervous system of these fish.

Predictability of the target stimulus for sensory-guided movement modulates early somatosensory cortical potentials

Objective To investigate the role of sensory modulation in the control of sensory-guided behaviour. Specifically, we hypothesized that early somatosensory evoked potentials (SEPs) would be facilitated during performance of continuous sensory-guided movement requiring sustained attention. Methods Median nerve SEPs were elicited via electrical stimulation and recorded from scalp electrodes while subjects performed tasks requiring continuous sensory–motor transformations. Subjects received a predictable (rhythmic amplitude modulation) or unpredictable (random amplitude modulation) amplitude varying tactile stimulus (frequency constant at 20 Hz) delivered to the tip of the index finger either alone or with the requirement to track it by modulating the isometric grip force produced by the opposite hand. Results Early SEP (N20-P27) amplitudes were differentially modulated during unpredictable tracking compared to sensory–motor controls. Specifically, N20 amplitudes were attenuated and P27 amplitudes were enhanced during sensory-guided tracking. Conclusions Sustained attention to task-relevant sensory stimuli differentially modulates areas within primary somatosensory cortex (S1) during a continuous sensory–motor transformation. Significance These data have implications for understanding the role of attention in regulating somatosensory cortices during sensory–motor behaviour.