Noise Envelope Research Articles

Passive acoustic classification of vessels in the Hudson River.

Stevens Institute of Technology is conducting research aimed at the development of a low‐cost passive acoustic system for detection and classification of underwater and surface threats. The experimental system is comprised of a hydrophone array and a stand alone acoustic buoy. Video and photographs of the passing ships were also captured simultaneously during the acoustic measurements. For classification purposes special attention was paid to extraction of the specific parameters of vessel acoustic signatures in high‐frequency band (10–60 kHz) using detection of envelope modulation on noise algorithm. The spectrum of the noise envelope contains shaft and blade frequencies and their harmonics. Parameters extracted include the frequency of the fundamental peak of the ship noise emission, the amplitude modulation of the fundamental tone, the number of peaks found in the spectrum, the slope of the spectral peaks, as well as the calculation of the total harmonic distortion. Parameters extracted from various records are then plotted together and their statistical analysis was applied for surface ship classification. [This work was supported by the U.S. Department of Homeland Security under Grant No. 2008‐ST‐061‐ML0002].

Roughness detection in fricative-like noise and tone stimuli

Audio (spectral) and modulation (envelope) frequencies both carry information in a speech signal. While low modulation frequencies (2-20Hz) convey syllable information, higher modulation frequencies (80-400Hz) allow for assimilation of perceptual cues, e.g., the roughness of amplitude-modulated noise in voiced fricatives, considered here. Psychoacoustic 3-interval forced-choice experiments measured AM detection thresholds for modulated noise accompanied by a tone with matching fundamental frequency at 125Hz: (1) tone-to-noise ratio (TNR) and phase between tone and noise envelope were varied, with silence between intervals; (2) as (1) with continuous tone throughout each trial; (3) duration and noise spectral shape were varied. Results from (1) showed increased threshold (worse detection) for louder tones (40-50dB TNR). In (2), a similar effect was observed for the in-phase condition, but out-of-phase AM detection appeared immune to the tone. As expected, (3) showed increased thresholds for shorter tokens, although still detectable at 60ms, and no effect for spectral shape. The phase effect of (2) held for the short stimuli, with implications for fricative speech tokens (40ms-100ms). Further work will evaluate the strength of this surprisingly robust cue in speech.

Analysis of frication noise modulation from a physical model

A physical model, built to investigate the aeroacoustic properties of voiced fricative speech, was used to study the amplitude modulation of theturbulence noise it generated. The amplitude and fundamental frequency of glottal vibration, relative positions of the constriction and obstacle, and the flow rate were varied. Measurements were made from pressure taps in the duct wall and the sound pressure at the open end. The high-pass filtered sound pressure was analyzed in terms of the magnitude and phase of the turbulence noise envelope. The magnitude and phase of the observed modulation was related to the upstream pressure. The effects of moving the obstacle with respect to the constriction are reported (representative of the teeth and the tongue in a sibilant fricative respectively). These results contribute to the development of a parametric model of the aeroacoustic interaction of voicing with turbulence noise generation in speech.

Stoichiometry of the Peripheral Stalk Subunits E and G of Yeast V1-ATPase Determined by Mass Spectrometry

The stoichiometry of yeast V(1)-ATPase peripheral stalk subunits E and G was determined by two independent approaches using mass spectrometry (MS). First, the subunit ratio was inferred from measuring the molecular mass of the intact V(1)-ATPase complex and each of the individual protein components, using native electrospray ionization-MS. The major observed intact complex had a mass of 593,600 Da, with minor components displaying masses of 553,550 and 428,300 Da, respectively. Second, defined amounts of V(1)-ATPase purified from yeast grown on (14)N-containing medium were titrated with defined amounts of (15)N-labeled E and G subunits as internal standards. Following protease digestion of subunit bands, (14)N- and (15)N-containing peptide pairs were used for quantification of subunit stoichiometry using matrix-assisted laser desorption/ionization-time of flight MS. Results from both approaches are in excellent agreement and reveal that the subunit composition of yeast V(1)-ATPase is A(3)B(3)DE(3)FG(3)H.

Gap detection in modulated noise: Across-frequency facilitation and interference

This study tested the hypothesis that a detection advantage for gaps in comodulated noise relative to random noise can be demonstrated in conditions of continuous noise and salient envelope fluctuations. Experiment 1 used five 25-Hz-wide bands of Gaussian noise, low-fluctuation noise, and a noise with increased salience of the inherent fluctuations (staccato noise). The bands were centered at 444, 667, 1000, 1500, and 2250 Hz, with the gap signal always inserted in the 1000-Hz band. Results indicated that a gap detection advantage existed in continuous comodulated noise only for Gaussian and staccato noise. Experiment 2 demonstrated that the advantage did not exist for gated presentation. This experiment also showed that the advantage bore some similarity to comodulation masking release. However, differences were also noted in terms of the effects of the number of flanking bands and the absence of a detection advantage in gated conditions. The detrimental effect of a gated flanking band was less pronounced for a comodulated band than for a random band. This study indicates that, under some conditions, a detection advantage for gaps carried by a narrow band of noise can occur in the presence of comodulated flanking bands of noise.

Measurement of Barkhausen noise and its correlation with magnetic permeability

The paper investigates applicability of the Barkhausen noise technique as a non-destructive testing method and its correlation with the magnetic hysteresis measurement. The hysteresis and the Barkhausen noise experiments were performed at laboratory and industrial configurations on a model series of open flat samples plastically deformed by mechanical tension. The sample magnetic field was measured with the help of a near-surface Hall sensor. The results proved interrelation between the magnetic differential permeability and the Barkhausen noise envelope. However, significant quantitative discrepancies between them were also obtained. The reasons of these deviations as well as the main measurement problems were discussed in order to help to standardize the Barkhausen noise technique and to extend a number of the used parameters for the non-destructive testing.

Aerodynamically-based parametric description of the noise envelope in voiced fricatives

In voiced fricatives, the radiated sound is composed of a harmonic component associated with the vibrating larynx and a noise component generated at a constriction in the oral cavity. The sound from the two sources interacts in a nonlinear way to produce a noise signal with an amplitude envelope modulated at the fundamental frequency of voicing. While voiced fricatives synthesized as a linear combination of harmonic and noise components are identifiable, it is recognized that the inclusion of the modulation improves the perceived naturalness of a synthesized token. The depth of modulation of the radiated noise, for a range of aerodynamic and acoustic variables, was measured experimentally using a dynamic mechanical model of the larynx and vocal tract. Glottal excitation arose from driven shutters representing the vocal folds; frication noise was produced by an orifice plate with a sharp-edged obstacle downstream. Based on the empirical data, a parametric description was developed to predict the depth and phase of amplitude modulation of the noise from the aerodynamic and acoustic conditions.

A Nonlinear Method for Stochastic Spectrum Estimation in the Modeling of Musical Sounds

We propose an original technique for separating the spectrum of the noisy component from that of the sinusoidal, quasi-deterministic one, for the sinusoids + transients + noise modeling of musical sounds. It also enables estimation of the time-domain noise envelope and detection of transients with standard techniques. The algorithm for spectrum separation relies on nonlinear transformations of the amplitude spectrum of the sampled signal obtained via fast Fourier transform, which allow to eliminate the dominant partials without the need for precisely tuned notch filters. The envelope estimation is performed by calculating the energy of the signal in the frequency domain, over a sliding time window. Several transformations (such as pitch shifting, time stretching, etc.) can be performed on the so-obtained stochastic spectrum prior to resynthesis. The synthesized sound is built via inverse fast Fourier transform with overlap-add method. The performance of the proposed algorithm is assessed on synthetic, instrumental, and natural sounds in terms of different quality measures

Level crossing rate of phase noise IM-DD optical systems in presence of interference

In this paper the joint probability density function of the envelope and the first time derivative of envelope, and phase and first time derivative of phase for signals in IM-DD optical systems are derived. The level crossing rate and the average fade duration for envelope and phase of sine wave plus narrowband Gaussian noise are given. The envelope of signal and its derivative are independent. The first time derivative of the signals has Gaussian distribution. .

Investigation of magnetic response to plastic deformation of low-carbon steel

In this work results of magnetic investigation of structure degradation of low-carbon steel due to plastic tensile strain are presented. Two series of magnetically closed window-shaped and open strip-shaped specimens were deformed to different strains up to 20% and measured after unloading. Magnetic hysteresis and Barkhausen noise measurements were done with magnetization parallel to the strain direction. Two-peak profiles of differential permeability and Barkhausen noise envelope were found and explained by splitting of the domain wall motion into two stages due to residual intrinsic stresses. Influence of generated dislocation tangles on magnetization process is also considered.

On the Autocorrelation of Complex Envelope of White Noise

About four decades ago, in an article in this transactions, Thomas Kailath pointed out that the autocorrelation of the complex envelope of white noise is not strictly an impulse function, even though when treated as an impulse in practical problems, it does lead to correct results. However, it is commonly assumed that by simply letting the bandwidth of a flat-bandlimited noise process to go to infinity, one obtains the result that the autocorrelation of the complex envelope of white noise equals an impulse function. In this correspondence, we show that 1) the limit operation has to be done carefully and 2) when done properly, it leads to the result in the Kailath's paper, which is different from a pure impulse function

Coherent and Squeezed States for Light in Homogeneous Conducting Linear Media by an Invariant Operator Method

With the choice of Coulomb gauge, we investigated coherent state and squeezed state of the light propagating through homogeneious conducting linear media with no charge density using quantum results of the LR invariant operator method. We described coherent and squeezed properties of electric and magnetic fields. The fields in coherent and squeezed states are decayed exponentially with time due to the conductivity of the media. We studied probability density of the coherent wave packet and the highly squeezed wave packets. The uncertainty relation between the two orthogonal phase amplitudes, â1 and â2, in coherent state is same as the uncertainty relation in vacuum number state. The envelope of the relative noise in coherent state alternately become large and small with time and position. The uncertainty relation between canonical variables are varied depending on the value of conductivity σ in squeezed state, but not lowered below ħ/2 which is quantum-mechanically acceptable minimum uncertainty.

Broadband noise filtering in random sequences of coherent pulses using the temporal Talbot effect

The exact power spectrum of the detected optical envelope of a train of random pulses after the temporal Talbot effect is computed. The input train into a Talbot device consists of a sequence of chirped Gaussian pulses whose appearance in the train is probabilistic. Dispersion provides a Talbot replica of the original train. The resulting noise spectrum shows narrow spectral windows below a broadband output noise envelope. The noise-envelope width depends on the value of the chirp, coinciding with the single-pulse spectrum only if the pulses are unchirped. The locations and width of the spectral windows depend on the values of the chirp and the temporal width of the pulses in the train. For wide pulses, high output harmonics, and low dispersive devices, these windows are cosine-squared modulated. The properties of this modulation depend only on the statistics of the appearance of the pulses. © 2004 Optical Society of America

Binaural unmasking of the periodic component in the envelope of an amplitude-modulated signal

A binaural unmasking of a tone component that is present in an amplitude-time noise envelope of a high-frequency signal is studied. The signal has the form of a sinusoidal carrier of frequency 2000–5000 Hz amplitude modulated by a low-frequency signal. The modulating function is a mixture of a 300-Hz tone (interaurally inphase or antiphase) and a dichotic masking noise within 0–400 Hz, this mixture being subjected to a half-wave linear rectification. The listener has to detect the rhythmic component in the modulating noise function. It is shown that, under the aforementioned conditions, the binaural difference in masking levels grows up to 25 dB with increasing carrier frequency but drastically decreases in the case of a masking of the low-frequency part of the basilar membrane in the vicinity of 300 Hz. The lateralization based on the interaural phase of a 100% amplitude modulation by a 300-Hz tone at a carrier frequency within 2000 to 5000 Hz also drastically decreases (in our experiments) when the low-frequency part of the basilar membrane is masked.

Pulse nonstationary processes generated by dynamic systems with random structure

Dynamic system with a random structure described by a set of the first-order stochastic differential equations (SDE) is used as a generating model of nonstationary pulse stochastic processes. Physically the system presents the combination of the so-called partial filters related to the isolated states of the considered process, switched by a Poissonian point process and excited by a vector delta-correlated stream of impulses with the randomly distributed energy. The filters’ outputs are components of the vector Markov continuous-jump process with statistics depending on the partial SDEs operators, intensity of switching process and distributions of the exciting impulses’ energies. The approach proposed was used as a simulation model of the Middleton “Class-A “generally non-Gaussian noise. The results demonstrate that the main features of statistical characteristics of the noise envelope are reproduced rather well with the help of a bistate system with random structure.

Shot noise in actual urban and industrial environments

AbstractShot noise has been measured in three different environments: an urban street, a factory, and a train station, and the results are presented in this Letter. The measurement system was designed to operate at UMTS band and to provide both phase and envelope of the shot noise. It has been found that the train station is not a very noisy environment. In the factory shot‐noise events are less frequent than on the urban street; however, noise pulses appear more grouped in bursts. Noise pulses exhibit a larger amplitude and shorter duration in the factory than in the street measurements. In both cases, shot‐noise pulses have very high amplitude and duration compared to the limits for UMTS signals. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 112–115, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10389

Wideband model of HF atmospheric radio noise

A model of the waveform generated by high‐frequency atmospheric radio noise is presented. Cumulative probability distributions of the noise envelope are derived and shown to be in good agreement with a large database collected from a wide range of noise environments. The model includes correlations in the waveforms that simulate the burst structure of measured atmospheric noise. The bandwidth dependence of the voltage deviation parameter, which parameterizes the impulsiveness of the noise, shows behavior that is qualitatively similar to a limited amount of measured data.

Magnetic gradiometry: a new method for magnetic gradient measurements

Instead of using a pair of different magnetic field sensors and differentiating their outputs in order to derive a magnetic gradient value, a single sensitive element can be used for measuring directly a magnetic gradient. This is done by the use of a stiff metallic string clamped at both ends and pumped with an AC current the frequency of which is tuned to the second eigenmode of the string. The string is excited at that eigenmode in the presence of a quasi-static magnetic gradient. Then, the corresponding mechanical displacements of the string can be measured by the use of an inductive technique with an instrumental noise envelope of less than ±10 −12 m, per 1 s measurement interval.

New methods of radar performances analysis

Original methods for radar detection performance analysis are derived for a fluctuating or non-fluctuating target embedded in additive and a priori unknown noise. This kind of noise can be, for example, the sea or ground clutter encountered in surface-based radar for the detection of low grazing angle targets and/or in high-resolution radar. In these cases, the spiky clutter tends to have a statistic which strongly differs from the Gaussian assumption. Therefore, the detection theory is no longer appropriate since the nature of statistics has to be known. The new methods proposed here are based on the parametric modelling of the moment generating function of the noise envelope by Padé approximation, and lead to a powerful estimation of its probability density function. They allow to evaluate the radar detection performances of targets embedded in arbitrary noise without knowledge of the closed form of its statistic and in the same way to take into account any possible fluctuation of the target. These methods have been tested successfully on synthetic signals and used on experimental signals such as ground clutter.

A comparison of low‐frequency radio noise amplitude probability distribution models

One of the most commonly modeled statistics in atmospheric radio noise studies is the noise envelope voltage amplitude probability distribution (APD). Although a number of models have been introduced to characterize atmospheric noise envelope APDs, the quantity of real data that exist to verify their accuracy is somewhat limited, especially in the ELF and VLF bands. This paper presents the results of a statistical analysis in which thousands of hours of ELF/VLF noise are processed to derive APDs, which are then compared with various APD models to determine which of the models is most accurate. The error criterion used to find the optimal parameters of each APD model, as well as to compare the models against each other, is the expected value of the log error squared (where the log error is the difference in decibels between the data histogram and the model histogram). This criterion provides a means by which the models may be evaluated and compared numerically. The most accurate model is found to depend on geographic location, time of year and day, bandwidth, and center frequency, but two of the simplest models (i.e., each with only two parameters) are found to give extremely good performance in general. These are the Hall and alpha‐stable (or α‐stable) models, both of which approximate the Rayleigh distribution for low‐amplitude values but decay with an inverse power law for high‐amplitude values. This paper concludes that the Hall model is the optimal choice in terms of accuracy and simplicity for locations exposed to heavy sferic activity (e.g., lower latitudes) and the α‐stable model is best for locations relatively distant from heavy sferic activity (e.g., the polar regions).