Showing papers on "Noise reduction published in 1982"

A Model for Radar Images and Its Application to Adaptive Digital Filtering of Multiplicative Noise

Abstract: Standard image processing techniques which are used to enhance noncoherent optically produced images are not applicable to radar images due to the coherent nature of the radar imaging process. A model for the radar imaging process is derived in this paper and a method for smoothing noisy radar images is also presented. The imaging model shows that the radar image is corrupted by multiplicative noise. The model leads to the functional form of an optimum (minimum MSE) filter for smoothing radar images. By using locally estimated parameter values the filter is made adaptive so that it provides minimum MSE estimates inside homogeneous areas of an image while preserving the edge structure. It is shown that the filter can be easily implemented in the spatial domain and is computationally efficient. The performance of the adaptive filter is compared (qualitatively and quantitatively) with several standard filters using real and simulated radar images.

An Improved Algorithm for Reprojecting Rays through Pixel Images

Abstract: It is often desired to calculate line integrals through a field of reconstructed CT density pixels for the purpose of improving CT image quality. Two algorithms widely published and discussed in the past are known to either degrade spatial resolution or generate errors in the results due to the discontinuous "square pixel" modeling of the reconstructed image. An algorithm is described, based on linear interpolation between pixels, which provides superior accuracy without unnecessary loss of resolution. It was tested on simulated data for a head section and on a narrow Gaussian density distribution. The experimental results demonstrated improved performance. The method is expected to prove useful for many types of post-reconstruction processing, including beam hardening, missing data, and noise supression algorithms.

Adaptive Algorithms for Estimating and Suppressing Narrow-Band Interference in PN Spread-Spectrum Systems

Abstract: Results of an investigation of algorithms for estimating and suppressing narrow-band interference in pseudonoise (PN) spread-spectrum digital communication systems are presented. Techniques for determining the coefficients of a linear, interference suppression filter are described, which are based on linear prediction and conventional spectral analysis methods. Numerical results are presented on the characteristics of the linear filter and on its effectiveness in suppressing the interference. The error rate performance of a receiver that employs the interference suppression filter followed by a PN correlator is determined based on the assumption that the combined noise and residual interference at the output of the PN correlator is Gaussian distributed. Performance results obtained by Monte Carlo simulation are also presented and compared with theoretical results.

System identification techniques for adaptive noise cancelling

Abstract: A general form of a noise canceller is derived, using a signal modeling approach The proposed structure combines two infinite impulse response filters: a noise canceller and a line enhancer A recursive prediction error algorithm is used to adaptively estimate the filter coefficients Preliminary simulation results on the performance of the generalized adaptive noise canceller are presented

Noise reduction via factor analysis in FT-IR spectra

Abstract: The application of factor analysis to reduce random noise in FT-IR spectra is described. By utilizing the total information content of all the spectra, it is possible to reduce the amount of random noise present in individual spectrum.

Effect of thickness on airfoil surface noise

Abstract: Noise emission from very small chord and very large chord airfoils was measured with eleven 0.63 cm microphones placed along a horizontal semicircle (4.57 m radius) that was centered at the leading edge of the test airfoil. The noise signals were analyzed by an automated spectrum analyzer which yielded 1/3-octave band sound pressure level spectra for each microphone, and the data were corrected to remove the effects of atmospheric attenuation and jet noise. It is found that the effect of thickness is large and must be accounted for in any fundamental airfoil noise theory that attempts to describe the noise emitted from real airfoils. Incident mean velocity gradients and compressibility must also be taken into account. The effect of thickness increases with frequency, with thick airfoils being quieter than thin ones.

Noise reduction apparatus for hybrid image sensor

Abstract: A document sensing device is herein disclosed whereby the signal-to-noise ratio inherent in a large-size image sensor is enhanced by a reduction in system noise. A plurality of photodetectors are connected to a plurality of storage MOSFETs. Two signal wires are connected to alternating groups of the MOSFETs. A shift register is provided which sequentially turns on the MOSFETs. The connections of the groups of MOSFETs and the sequential turn-on sequence are both preselected such that at the same time one group of MOSFETs is outputting a composite signal (information plus noise) on one signal wire, the immediately preceding group of MOSFETs is outputting a signal (noise only) on the other signal wire. Upon the combination of the signals in a differential amplifier, the noise signal is thus eliminated from the composite signal.

Active attenuation of noise—The monopole system

Abstract: Proposals have been made to attenuate noise propagating down a duct by adding an antiphase copy of the primary noise. In a number of configurations, two or three sources had been used to produce the secondary noise, but a successful system with one source had not been realized. The conventional monopole system is analyzed and the reason why this type of monopole secondary source is not a practical solution is investigated. A modified system with a new solution of the problem is developed.

Flight effects of fan noise

Abstract: Simulation of inflight fan noise and flight effects was discussed. The status of the overall program on the flight effects of fan noise was reviewed, and flight to static noise comparisons with the JT15D engine were displayed.

Guide to the evaluation of human exposure to noise from large wind turbines

Abstract: Guidance for evaluating human exposure to wind turbine noise is provided and includes consideration of the source characteristics, the propagation to the receiver location, and the exposure of the receiver to the noise. The criteria for evaluation of human exposure are based on comparisons of the noise at the receiver location with the human perception thresholds for wind turbine noise and noise-induced building vibrations in the presence of background noise.

Helium speech enhancement using the short-time Fourier transform

Abstract: Speech produced in a hyperbaric helium-oxygen atmosphere suffers a variety of distortions which render it virtually unintelligible. This paper describes a new system for helium speech enhancement based on a short-time Fourier transform signal representation. The algorithm is robust, allows nonlinear warping of the spectral envelope, and includes provisions for generating the enhanced speech at a reduced sampling rate. Noise reduction by spectral subtraction can be included, and the algorithm is amenable to real-time implementation on an array processor. A review of helium speech phenomena is included to motivate the design, and a new result for the behavior of formant bandwidths is given. The results of formal intelligibility tests are reviewed, These tests show an improvement in intelligibility from about 40 to 70 percent. The tests also show that the noise reduction scheme is detrimental to intelligibility, but fail to conclusively resolve the importance of a non-linear formant frequency shift.

Noise reduction apparatus

Abstract: A noise reduction apparatus for reducing noises contained in a television picture signal is realized by comprising a low pass filter for filtering out noise components together with higher frequency components of the picture signal, the latter being compensated thereafter in response to detection of edge portions of the picture, as well as realized by utilizing interframe correlation of the television picture signal for reducing random noise components together with interframe varying components caused by motion of the picture, the latter being compensated thereafter in response to detection of the motion of the picture, which motion is discriminated by interframe variation of a group of picture elements. As a result, the noise reduction of the picture signal can be efficiently attained without any deterioration of picture quality, which is conventionally accompanied therewith.

Noise reduction means for a dynamic stabilizer for synchronous machines having torsional oscillations

Abstract: Signal conditioning apparatus for reducing the noise frequencies of a speed sensing means signal being fed into a compensating means for compensating the output of a synchronous generator for the effect of torsional oscillation between masses in the main AC generator system. The signal conditioning apparatus includes two speed sensing transducers mounted 180° apart on opposite sides of a tooth gear wheel and summing the two FM output signals from the transducers to eliminate odd harmonics of the synchronous frequency in FM noise due to eccentricity. The preferred embodiment of the invention reduces the remaining noise from the sensed speed signal by the use of a three-pole Butterworth low-pass filter in combination with a notch filter tuned to the turbine-generator synchronous frequency to thereby reduce the unwanted noise to a large degree while providing a minimal phase shift to the sensed speed signal. Another embodiment of the invention may be used to determine the machining accuracy of the toothed gear wheel.

Reduction of optical phase noise in semiconductor lasers

Abstract: There are several applications of highly coherent semiconductor lasers, especially in coherent optical-fibre communications systems and optical-fibre sensors. Optical phase noise is extremely important in these applications. Here we report preliminary results from a simple technique whereby phase noise in semiconductor lasers may be reduced. Initial results demonstrate a phase-noise reduction of typically 20 dB. Developments of the technique should permit reduction towards the shot noise limit.

An interpretation of error spectrum shaping in digital filters

Abstract: Error spectrum shaping is used in digital filters to reduce roundoff noise. There are several other filter structures which can also reduce roundoff noise. Are these methods of noise reduction in any way related? This paper shows that optimal error spectrum shaping is a method of increasing the word length of accumulators and internal variables, i.e., it is, in its optimum form, extended precision arithmetic. Furthermore there is no hardware advantage to be gained with optimum ESS as compared to traditional methods of implementing extended precision arithmetic.

Biological signal amplifier system with noise level reduction

Abstract: A biological amplifier system is disclosed for displaying the cardiac conduction system activity, particularly the His bundle activity on a beat-to-beat basis by a non-invasive technique. Plural sets of bipolar leads are connected by electrodes to the body surface so as to obtain the same biological signal on each set. The leads are connected in parallel to plural low noise amplifiers which provide simultaneous but separate amplification of the same signal. The amplified signals are added together in a summing circuit with the effect of noise reduction by averaging the random noise components. Noise reduction is further enhanced by use of negative feedback to a reference electrode and by use of a low pass filter and notch filter.

Special effects noise reduction in a rotary head reproduction apparatus

Abstract: A magnetic video reproducing apparatus employing a well-known rotational two-head system, a helical scan system and an azimuth system is adapted to make high speed reproduction of a magnetic tape (2) having a video signal recorded in video tracking pitches larger than the width of the reproducing heads and comprises a capstan servo circuit (15) including speed ratio setting circuits (17, 20), a phase control circuit (19) and a speed control circuit (21), wherein the traveling speed of the magnetic tape (2) for high speed reproduction is adapted to be precisely an odd number of times for normal speed reproduction. The speed control circuit (21) is made to accurately control the traveling speed of the magnetic tape (2) to be of the prescribed value. The phase control circuit (19) is made to control the traveling phase of the magnetic tape (2) to be constant.

Noise reduction circuit for a video signal

Abstract: A noise reduction circuit comprises a lowpass filter supplied with a luminance signal having a noise component of an input video signal, for eliminating a high-frequency component including the noise component, a first circuit for subtracting an output signal of the lowpass filter from the luminance signal, in a state where a rise in the level of the luminance signal is delayed by a predetermined time τ from the start of a rise in the output of the lowpass filter, where the output signal of the lowpass filter has a rise time τ, and a second circuit for amplitude-limiting a subtracted output of the first circuit and subtracting the amplitude-limited output from the luminance signal, to obtain a luminance signal eliminated of the noise.

Noise control composite

Abstract: A composite for use on submarines and surface craft for controlling self-erated noise when listening with sonar. The composite includes two layers of PVF2 transducers separated by a layer of phase shifting or absorbing material. The inner transducer senses noise from the ship and subtracts this from the signal from the outer transducer representing noise plus the desired signal. In a second mode the sensed noise is regenerated through the outer transducer 180° out of phase to cancel the noise and allow more accurate detection.

Noise reduction for FM stereophonic systems and particularly useful in television audio systems

Abstract: In a television system for recovering a stereophonic sound signal including a subcarrier signal, apparatus is provided including a bandpass filter for sensing the noise density of the recovered sound signal. A detector generates a control signal corresponding to the noise density sensed by the filter. The control signal is used to progressively attenuate the level of the subcarrier signal in response to increases of the sensed noise density. Although this gradually reduces the stereophonic separation, it provides a corresponding increase in the signal-to-noise ratio of the resulting reproduced stereophonic signal.

FIR filter structures having low sensitivity and roundoff noise

Abstract: A class of structures for FIR filters is presented, which exhibits reduced coefficient sensitivity and superior roundoff noise properties as compared to the direct form realization. It is shown that using fixed-point arithmetic, these structures achieve the same accuracy and about the same roundoff noise as those obtained in the floating-point implementationn. The optimum structure to achieve the minimum roundoff noise can be found; in most cases near optimum results are easily obtained by simple permutations and combinations of the impulse response coefficients. While a serial form realization of these structures requires a certain amount of software complexity, a parallel form, on the other hand, does not require additional complexity.

Handbook of Urban Rail Noise and Vibration Control

Abstract: This handbook is a guide to the prediction and control of all types of urban rail transit noise, ranging from train noise heard by the community at large to noise in maintenance shops heard only by transit employees. The topics covered include: acceptability criteria for transit related noise and vibration; the general characteristics of urban rail noise and vibration; techniques and equipment for measurement of noise and vibration; control of transit vehicle noise and vibration; control of community noise from surface tracks and aerial structures; prediction and control of groundborne noise and vibration; control of noise in transit stations; control of noise from station ancillary equipment such as air-conditioning systems and fan and vent shafts; control of noise around yards and shops; control of wheel squeal noise; and control of pressure transients in subway tunnels. The handbook is primarily intended for transit engineers, although it should also be useful for transit system executives and transit system acoustical consultants. Extensive bibliographic information is provided for readers looking for more detailed information. Also, for those interested in a general overview of urban rail noise and vibration, the executive digest of this handbook is available as a separate document. (a) (Author/TRRL)

The effect of a television digital noise reduction device on fluoroscopic image quality and dose rate.

Abstract: In conventional fluoroscopy, the current, and therefore the dose rate, is usually determined by the level at which the radiologist visualizes a just tolerable amount of photon "mottle" on the video monitor. In this study, digital processing of the analogue video image reduced noise and generated a television image at half the usual exposure rate. The technique uses frame delay to compare an incoming frame with the preceding output frame. A first-order recursive filter implemented under a motion-detection scheme operates on the image of a point-by-point basis. This effective motion detection algorithm permits noise suppression without creating noticeable lag in moving structures. Eight radiologists evaluated images of vesicoureteral reflux in the pig for noise, contrast, resolution, and general image quality on a five-point preferential scale. They rated the digitally processed fluoroscopy images equivalent in diagnostic value to unprocessed images.

Noise reduction in speech using adaptive filtering I: Signal processing algorithms

Abstract: Adaptive filtering is employed in configurations to filter narrow‐band speech corrupted by noise. These configurations utilize either an independent sample of the input noise or rely on correlation properties of the speech to accomplish cancellation. Necessary constraints on the algorithms to retain and/or improve intelligibility for normal and hearing‐impaired populations are presented. Previous work with the LMS algorithm is compared to the performance resulting from new methods which address the problem created by widespread eigenvalues in the speech plus noise correlation matrix. It is shown that failure to deal with this problem in the single reference application results in a muffling resonant distortion of the speech spectrum. Spectral averages of the original and processed versions of the speech segments are compared to determine improvement. Auditory tests are presented in the companion paper.

Nonstationary 2-D recursive filter for speckle reduction

Abstract: Speckle noise exists in all types of coherent imagery such as synthetic aperture radar, acoustic imagery and laser illuminated imagery. Speckle can be reduced by averaging over several uncorrelated speckle images of the same object when these are available. In this paper, we attempt to reduce speckle noise from a single speckle image by using adaptive digital image restoration techniques. Many speckle noise reduction algorithms assume speckle noise is multiplicative. We model the speckle according the exact physical process of coherent image formation. Thus, the model includes signal-dependent effects and accurately represents the statistical properties of speckle. A linear minimum mean-square error filter is derived based on our speckle model and a nonstationary image model. The filter responds adaptively to the signal-dependent speckle noise and the nonstationary mean and variance of the original image. The necessary parameters are estimated from the noisy image. The 2-D recursive implementation of this filter is developed as a fast computation algorithm.

Device for noise reduction in digital fluoroscopy systems

Abstract: Apparatus for reducing the effect of x-ray statistical noise and electronic noise in a fluorographic system that displays an x-ray image on a television screen. Analog video signals based on the x-ray image are amplified logarithmically and digitized to yield live pixel signals. Processed pixel signals are averaged in a full image store or memory. Motion is detected by subtracting the stored pixels from the live pixels on a pixel-by-pixel basis in an ALU. The difference resulting from subtraction is used as part of an address to a look-up table (LUT) which contains values equivalent to the difference signals times a noise reduction multiplicative factor, K. The other part of the addresses if Live pixel value. There are several replications of the look-up tables each relating to a particular brightness level range. The one selected is determined by the live signal part of the address which relates to brightness. The K times the difference signals in the ranges are chosen so the amount of noise reduction varies with brightness level as desired for logarithmic signals. The pixels processed as explained above are added in-phase with the stored and averaged pixels and returned to the corresponding full image memory locations.

A Kalman filter procedure for the processing of the electroencephalogram

Abstract: In the present paper a Kalman filter procedure is illustrated for the reduction of muscular noise superimposed to the electroencephalografic traces (EEG). Such a noise, in fact, has a bandwidth which overlaps the signal carrying the information content useful for the clinical standpoint and, therefore, can not be removed by means of classical digital filtering. A Markov model is used for identifying the signal model (supposed generated by an ARMA process) and the noise model (conceived on the basis of experiments of neurophysiological evidence). The experimental results show a good performance of the filter on the discrete-time EEG signal which is also quantified by the spectral information and the values of the prediction error of the filter itself. Comparison is then carried on with a classical low-pass FIR filter (mostly used in practice) which can not be aggressive enough towards the noise contained in the signal bandwidth but which can undoubtly ameliorate the performance of the Kalman filter.