Showing papers on "Noise measurement published in 1985"

Adaptive Noise Smoothing Filter for Images with Signal-Dependent Noise

Abstract: In this paper, we consider the restoration of images with signal-dependent noise. The filter is noise smoothing and adapts to local changes in image statistics based on a nonstationary mean, nonstationary variance (NMNV) image model. For images degraded by a class of uncorrelated, signal-dependent noise without blur, the adaptive noise smoothing filter becomes a point processor and is similar to Lee's local statistics algorithm [16]. The filter is able to adapt itself to the nonstationary local image statistics in the presence of different types of signal-dependent noise. For multiplicative noise, the adaptive noise smoothing filter is a systematic derivation of Lee's algorithm with some extensions that allow different estimators for the local image variance. The advantage of the derivation is its easy extension to deal with various types of signal-dependent noise. Film-grain and Poisson signal-dependent restoration problems are also considered as examples. All the nonstationary image statistical parameters needed for the filter can be estimated from the noisy image and no a priori information about the original image is required.

Noise suppression system

Abstract: An improved noise suppression system (400) is disclosed which performs speech quality enhancement upon speech-plus-noise signal available at the input (205) to generate a clean speech signal at the output (265) by spectral gain modification. The noise suppression system of the present invention includes a background noise estimator (420) which generates and stores an estimate of the background noise power spectral density based upon pre-processed speech (215), as determined by the detected minima of the post-processed speech energy level. This post-processed speech (255) may be obtained directly from the output of the noise suppression system, or may be simulated by multiplying the pre-processed speech energy (225) by the channel gain values of the modification signal (245). This technique of implementing post-processed signal to generate the background noise estimate (325) provides a more accurate measurement of the background noise energy since it is based upon much cleaner speech signal. As a result, the present invention performs acoustic noise suppression in high ambient noise backgrounds with significantly less voice quality degradation.

Automatic background noise estimator for a noise suppression system

Abstract: An improved background noise estimator (320) is disclosed for use with a noise suppression system (300) for generating an estimate of the background noise power spectral density provided to noise suppressor (310), which performs speech quality enhancement upon the pre-processed speech-plus-noise signal available at the input to generate a clean post-processed speech signal at the output. Background noise estimator (320) utilizes an energy valley detector based upon post-processed speech to perform the speech/noise classification, and a noise spectral estimator based upon pre-processed speech to generate an estimate of the background noise power spectral density. As a result, the background noise estimate supplied to the noise suppressor is a more accurate measurement of the background noise energy, since it is performed during a more accurate determination of the occurrences of pauses in the speech.

Effect of initial condition on subsonic jet noise

Abstract: The initial boundary-layer state can significantly affect the radiated noise from an axisymmetric jet. Jets with initially laminar boundary layers are found to emit more noise. Thus, 'cleaner' far-field noise characteristics are achieved in tripped jets. Data suggest that the additional noise in the initially laminar case partly originates from the first stage of pairing of the coherent shear-layer vortices.

X-Band Monolithic Series Feedback LNA

Abstract: An X-band monolithic three-stage low noise amplifier (LNA) employing series feedback has demonstrated 1.8 dB noise figure with 30.0 dB gain and an input VSWR less than 1.2:1 at 10 GHz. The key to this design is using monolithic technology to obtain an exactly repeatable series feedback inductance to achieve a simultaneous noise match and input VSWR match.

Noise modeling in submicrometer-gate two-dimensional electron-gas field-effect transistors

Abstract: Noise modeling in TEGFET's which provides good results in agreement with the experimental findings is presented. The influence of the main technological parameters on the noise figure and associated gain is given for operating frequencies up to 60 GHz. A comparison between TEGFET's and MESFET's is carried out. A new method for calculating the noise and gain performances of FET's is then proposed.

Signal Recovery from Noise in Electronic Instrumentation

Abstract: Low-pass filtering and visual averaging multiple time averaging and drift phase-sensitive detector methods spectral view of signal recovery 1/F noise frequency response calculations frequency-domain view of the phase-sensitive detector digitation and noise magnitude determination for transient signals of known shape and timing measurement of the time of occurrence of a signal transient.

Noise and chaos in a fractal basin boundary regime of a Josephson junction.

Abstract: By digital simulations and experiment, we study a Josephson system in a highly nonlinear regime. High experimental noise values appear to correspond in simulations to intrinsic chaotic motion in some regions and to noise-induced hopping between periodic solutions in others. Focusing on the latter, we find correlation between high noise sensitivity and the fractal dimension of the boundary between the basins of the periodic attractors. We show that if enough noise is present to push the orbits into the basin boundary, behavior similar to intrinsic chaos results.

Equivalent-noise model for contrast detection and discrimination.

Abstract: Models for the detection and the discrimination of low-contrast signals by human observers typically assume that the observer is limited by the filtering action of the visual system and by the noisy character of its processing. For some models both the filtering and the noise can be represented by a noise in the stimulus domain, the input equivalent noise of the model. We derive some formulas for computing this noise, describe the calculation of a sample, and discuss some implications of this approach.

Measurement of FM noise, AM noise, and field spectra of 1.3 µm InGaAsP DFB lasers and determination of the linewidth enhancement factor

Abstract: The FM and AM noise spectra of 1.3 μm InGaAsP DFB lasers are measured in the frequency range from dc to 4 GHz. The relaxation resonances appearing in these spectra are compared to the semiclassical theory of laser noise. All the resonance parameters, i.e., the linewidth enhancement factor α, the resonance frequency f R , and the damping constant γ e , are determined from the FM noise spectra by successful curve fitting. The estimated value of α is 2.2. Field spectra for various bias currents are measured by using optical heterodyne detection. Theoretical lineshapes are obtained by using four noise-parameter values which have been determined from the FM noise and the linewidth measurements. The results are in excellent agreement with the measured spectra. This agreement verifies the estimation that \alpha = 2.2.

Some acoustic-phonetic correlates of speech produced in noise

Abstract: Acoustical analyses were carried out on the digits 0-9 spoken by two male talkers in the quiet and in 90 dB SPL of masking noise in their headphones. The results replicated previous studies demonstrating reliable increases in amplitude, duration and vocal pitch while talking in noise. We also found reliable differences in the tilt of the short-term spectrum of consonants and vowels. The results are discussed in terms of: (1) the development of algorithms for recognition of speech in noise; (2) the nature of the acoustic changes that take place when talkers produce speech under adverse conditions such as noise, stress or high cognitive load; and, (3) the role of training and feedback in controlling and modifying a talker's speech to improve performance of current speech recognizers.

On the probability density of signal-to-noise ratio in an improved adaptive detector

Abstract: The main advantage of our previously presented [10] principal-component method of adaptive detection, in comparison with the method based on the inverse of the estimated covariance matrix, is that much less data is required to produce a given, needed level of SNR with high probability. In this paper we present an outline of the derivation of the approximate probability density of the SNR for this adaptive detector. To simplify the derivation we assume that the noise consists of a strong gaussian rank-one-covariance interference component plus a component of white gaussian background noise. The approximations and the final probability density are tested through simulation.

Atmospheric Radio Noise: Worldwide Levels and Other Characteristics

Abstract: The determination of radio communication system performance is a matter of proper statistical treatment of both the desired signal and the real-world noise (or interference) processes. System performance is highly dependent on the detailed statistical characteristics of both the signal and the noise as well as the single parameter: signal-to-noise ratio (which is sometimes the only parameter considered). Generally, the computation of the desired signal characteristics over a given path can be made reasonably accurately. This is not the case when it comes to estimating the noise level and other required noise characteristics. Existing noise models consist primarily of the worldwide atmospheric noise maps contained in CCIR Report 322 and estimated man-made noise levels given in CCIR Report 258. In addition, there are numerous other special purpose models. There is a need for an overall, comprehensive usable noise model for application to telecommunication problems. One needed task that has been accomplished toward the goal of obtaining such an overall model is the development of an improved atmospheric noise model. The existing worldwide atmospheric noise model (CCIR Report 322) was developed from approximately 4 years of measurements from a worldwide network of 16 measurement stations. This network made measurements for 5 years (longer in a few cases) past the completion of CCIR Report 322 in 1963. Also, additional data are now available from other locations, primarily many years of data from 10 Soviet measurement stations. All these additional data have been analyzed and an updated worldwide atmospheric noise model has been prepared in both graphical and numerical forms. Results of this analysis show substantial “corrections” (on the order of 20 dB for some locations) to the 1 MHz noise level values given by CCIR Report 322. It is the purpose of this report to

Optimum Noise Measure Terminations for Microwave Transistor Amplifiers (Short Paper)

Abstract: The noise performance of the individual stages in a multistage low-noise amplifier can be quantified by means of the noise measure as proposed by Haus and Adler [4]. The minimization of the noise measure of a given active two-port device is of direct interest to the designer of such amplifiers. A new means of obtaining circles of constant noise measure in the source reflection coefficient plane is presented here. These circles can be used to determine the value of the minimum noise measure for a given active device and the associated source termination. The validity of the new method has been verified by comparison with results obtained using existing equations for the admittance plane and also by experiment.

Electromigration detection by means of low-frequency noise measurements in thin-film interconnections

Abstract: Low-frequency noise power spectral densities associated with displacements of atoms caused by electromigration were measured on Al-Si (1 percent) resistors at various current densities in the frequency range 5 × 10-2 ÷ 2Hz. The temperature of the resistors was the one set by the current density itself, all the samples having been tested at room temperature. After noise measurement, each resistor was subjected to the current density at which the measurement was performed up to failure. The total electromigration power, measured in the frequency interval 0.1 ÷ 1 Hz was plotted as a function of the failure time for three different series of resistors obtained by means of an RF sputtering process. The measurement system and the characteristic features of the electromigration spectra are described.

Some experimental and theoretical results using a new adaptive filter structure for noise cancellation in the presence of crosstalk

Abstract: The application of adaptive filters in noise cancelling often requires the relative placement of the two transducers at a distance that necessitates a large order filter in order to obtain an adequate output signal-to-noise ratio. A new adaptive filter structure is introduced that permits a closer placement of the transducers and that allows the cancellation of noise in the presence of crosstalk. Algorithms are developed for the new transversal and lattice structures. Simulations show considerable improvement in mean-square error over that obtained with standard noise cancelling algorithms.

A characterization of Arctic undersea noise

Abstract: Arctic undersea noise is investigated and partially characterized by a probability model suggested by exploration of a sample of such noise. The large size of the data set makes this possible. The model is that of a mixed spectrum, with stationary Gaussian noise intermixed with random sinusoids, and occasional high intensity impulsive noise bursts, which are very short‐lived. Due to the complex behavior of the random sinusoids, the noise cannot be considered as stationary in the time frame (10 min) investigated. The validity of the model is checked by testing model predictions against the actual data. In particular, this model makes some predictions about the type of spectrum observed, and these predictions are tested by a nonlinear filtering of the periodogram. A running median filter is used and is shown to asymptotically estimate the spectrum of the Gaussian noise. This filter seems to work fairly well on the data.

Propagation of propeller tone noise through a fuselage boundary layer

Abstract: In earlier experimental and analytical studies, it was found that the boundary layer on an aircraft could provide significant shielding from propeller noise at typical transport airplane cruise Mach numbers. In this paper a new three-dimensional theory is described that treats the combined effects of refraction and scattering by the fuselage and boundary layer. The complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The model for the incident waves is a near-field frequency-domain propeller source theory developed previously for free field studies. Calculations for an advanced turboprop (Prop-Fan) model flight test at 0.8 Mach number show a much smaller than expected pressure amplification at the noise directivity peak, strong boundary layer shielding in the forward quadrant, and shadowing around the fuselage. Results are presented showing the difference between fuselage surface and free-space noise predictions as a function of frequency and Mach number. Comparison of calculated and measured effects obtained in a Prop-Fan model flight test show good agreement, particularly near and aft of the plane of rotation at high cruise Mach number.

QANI Trellis-coded signal structure

Abstract: A signal structure for high speed Trellis coded data communications selects each signal point in the structure to attain a low probability of error in the presence of both additive noise and multiplicative noise. Viterbi decoding is modified to take account of the multiplicative noise energy content of the received signal.

Discrete lorentzian structure in low frequency voltage noise spectra of very small area Josephson tunnel junctions

Abstract: We report the results of low frequency voltage noise measurements on very small area (A = 0.05 to 1 μm2) Nb-Nb 2 O 5 -PbBi tunnel junctions as a function of tunnel junction quality and over a wide range of voltage and temperature. We find that the noise spectrum S v in our bandwidth (1Hz to 25.6kHz) is largely composed of a small number (2-3) of distinct Lorentzian components each of which can be characterized by its own voltage and temperature dependent magnitude and mean rate. These lorentzian components provide a powerful means to probe the actual microscopic fluctuation events which lead to 1/f noise in larger devices. The ensemble average spectrum of our devices trends about a 1/f frequency dependence and has a magnitude proportional to (IR j )2and 1/A. We have used our results to establish the intrinsic low frequency energy sensitivity of d.c. SQUIDs made with shunted tunnel junctions.

Noise behavior of 1-µm gate-length modulation-doped FET's from 10 -2 to 10 8 Hz

Abstract: Measured equivalent gate noise voltage spectra of 1-µm gate-length MODFET's, for the frequency range of 0.01 Hz-100 MHz, are presented. They indicate that the noise consists of several high-intensity trap-related generation-recombination (g-r) noise components superimposed on a background 1/f noise. The g-r noise is reduced when the Al mole-fraction is lowered. The same occurs when the gate reverse bias is increased. At 100 K the g-r noise bulge moves towards subaudio frequencies clearly revealing the 1/f noise.

Effect of quantization noise on visual signal detection in noisy images.

Abstract: Data inaccuracy due to amplitude quantization in digital imaging systems can be viewed as a form of random noise. The effect of this noise is to reduce the accuracy of decisions based on image data. Experimental results are presented to demonstrate the reduction in human-observer decision accuracy due to quantization noise in addition to white Gaussian noise. There is a significant reduction when the ratio Q/σp is greater than unity, where Q is the quantization-step amplitude and σp is the standard deviation per pixel of the uncorrelated image noise.

Accurate noise measurements of superconducting quasiparticle array mixers

Abstract: We have constructed a 30-40 GHz test apparatus which allows us to measure the noise temperatures of SIS mixers with an accuracy of better than ±1K. This is a factor of six improvement over earlier measurements. The most accurate measurement made thus far of a mixer which uses a single Pb-alloy junction yielded T m = 9.2 ± 0.9 K; and mixer gain: G m = 0.240 ± 0.005. In addition, SIS mixers employing arrays of N = 1, 5, 10, 25, and 50 tunnel junctions in series have been tested. The input power required to saturate the array mixers was found to increase as N2and the gain and noise temperature of the array mixers were independent of N.

Absolutely optimum array filters for sensor arrays

Abstract: A family of array filters is derived for processing the recorded measurements of an array of sensors with the purpose of attenuating coherent noise interfering with a desired signal. One member of this family is the absolutely optimum array filter (AOAF), which minimizes the magnitude squared of the array rejection response subject to an all-pass condition for the desired signal. The AOAF is shown to have an array rejection response where both the width of the main lobes and the height of the sidelobes are reduced to zero.

Low-noise operation in buried-channel MOSFET's

Abstract: Noise measurements in buried-channel MOSFET's are presented on various operating conditions. A new noise source has been observed in the weak inversion regime of the MOSFET's. By avoiding this noise source and other known noise sources in buried-channel devices, a good noise performance of MOS analog circuits has been obtained.

Method and apparatus for testing communication systems

Abstract: A microcomputer controlled apparatus and method for testing communication lines including circuits serving multiple functions in the measurements of line electrical and noise characteristics. A current divider, an analog to digital converter, a constant current source, various filters and an RMS-to-DC converter are used to perform A.C. and D.C. voltage and current measurements, resistance measurement and noise measurement. Capacitance measurement circuits and method utilize a buffer for isolating the capacitance on the wire measured from other capacitance sources.

Machinery Noise Measurement

Abstract: Designed for engineers with little or no training in noise measurement, this practical handbook provides a thorough grounding in machinery acoustics, techniques crucial for the design of today's quieter machines. After a discussion of fundamental acoustic terminology; the authors describe various methods for machinery sound power measurement in free field, in semi-reverberant space, and in a reverberant room. Other sections consider noise measurement on nominally identical small machines, sound intensity measurement, and the new analogue and digital noise measuring equipment. In an era of growing noise pollution, this book will be very useful to acoustic engineers and equipment designers responsible for producing quieter machines.

Optimisation of Wedge and Strip Anodes

Abstract: We describe the Wedge and Strip Anode (WSA) position read-out system and compare the performance of currently used WSAs with that of Resistive Disk Anodes (RDAs). We show that for small systems the WSA can outperform the RDA while for larger systems the RDA cannot be used at all due to size limitations. We discuss noise in WSAs and present a comprehensive optimisation scheme based on a model for the WSA capacitance [1] which is capable of reducing the electronic noise by a factor of up to 6 compared with current WSAs. We present capacitance, noise and position resolution measurements of several WSAs with active diameters of up to 200mm. We describe a simple technique for the manufacture of WSAs and use this to produce WAs on thin metallised polymer film as an alternative noise reduction method. We discuss a special low noise application of WSAs to spectroscopy. The conclusion is reached that in most cases RDAs can be advantageously replaced by WSAs.