Showing papers on "Noise (signal processing) published in 1984"

An adaptive filtering algorithm using an orthogonal projection to an affine subspace and its properties

Abstract: The LMS algorithm and learning identification, which presently are typical adaptive algorithms, have a problem in that the speed of convergence may decrease greatly depending on the property of the input signal. To avoid this problem, this paper presents a geometrical discussion as to the origin of that defect, and proposes a new adaptive algorithm based on the result of the investigation. Comparing the convergence speeds of the proposed algorithm and the learning identification by numerical experiment by computer, great improvement was verified. The algorithm is extended to a group of algorithms which includes the original algorithm and the learning identification, which are called APA (affine projection algorithm). It is shown that APA has some desirable properties, such as, the coefficient vector approaches the true value monotonically and the convergence speed is independent of the amplitude of the input signal. Clear conclusions are also obtained for the problem as to what noise is included in the output signal when an external disturbance is impressed or the degree of the adaptive filter is not sufficient.

A Prony method for noisy data: Choosing the signal components and selecting the order in exponential signal models

Abstract: Prony's method is a simple procedure for determining the values of parameters of a linear combination of exponential functions. Until recently, even the modern variants of this method have performed poorly in the presence of noise. We have discovered improvements to Prony's method which are based on low-rank approximations to data matrices or estimated correlation matrices [6]-[8], [15]-[27], [34]. Here we present a different, often simpler procedure for estimation of the signal parameters in the presence of noise. This procedure has received only limited dissemination [35]. It is very close in form and assumptions to Prony's method. However, in preliminary tests, the performance of the method is close to that of the best available, more complicated, approaches which are based on maximum likelihood or on the use of eigenvector or singular value decompositions.

Two-input crosstalk-resistant adaptive noise canceller

Abstract: A two-input crosstalk-resistant adaptive noise canceller receives a primary input signal including a desired speech signal portion and an undesired noise signal portion and also receives a reference input signal having a reference noise input portion and a crosstalk speech portion. The canceller has first and second summer means and first and second adaptive filter means. The first summer means provides a canceller output signal which is the difference between the primary input signal and the first adaptive filter output signal. The canceller output signal is applied to the reference input of the second adaptive filter and to one of a pair of error-control inputs of the first adaptive filter. The second error-control input of the first adaptive filter is provided by the signal at the output of the second adaptive filter, which receives a single error-control input signal from the output of the second summer means. The second summer provides an output signal which is the difference between the reference input signal and the second adapter filter output signal. With the correlation bias between the desired primary input (speech) signal and the crosstalk (speech) signal in the reference input substantially reduced, the canceller output signal is then related substantially only to the primary input desired signal.

Pulse-to-Pulse Coherent Doppler Sonar Signal Processing Techniques

Abstract: In this paper we present and discuss techniques for the computation of the mean and spectral variance of a pulse-to-pulse coherent sonar signal, leading to the measurement of mean water velocity and turbulence. The use of an autocovariance algorithm associated with a dual-pulse repetition rate (PRF) method is recommended. The dual-PRF method allows removal of velocity ambiguities due to signal sampling and also offers a convenient means for the estimation and removal of the receiver noise which otherwise would strongly bias the spectral variance measurements. The performances of the method are illustrated by presentation and discussion of data acquired in a tidal flow.

Robust Wiener- Kolmogorov theory

Abstract: A minimax formulation is considered for the problem of designing robust linear causal estimators of linear functions of discrete-time wide-sense stationary signals when knowledge of the signal and/or noise spectra is inexact. The solution is given (under mild regularity conditions) in terms of a least favorable pair of spectra, thus reducing the minimax problem to a direct maximization problem which in many cases can be solved easily. It is noted that this design method leads, in particular, to robust n -step predictors, robust causal filters, and robust n -lag smoothers. The method of design is illustrated by a thorough development of the special case of one-step noiseless prediction. Further, solutions are given explicitly for the problem of robust causal filtering of an uncertain signal in white noise, and numerical examples are given for this case which illustrate the effectiveness of this design.

Noise suppressor for electronic endoscope

Abstract: A noise suppressor is provided for an electronic endoscope which incorporates a diathermic cutter or an ultrasonic diagnosis system. The electronic endoscope utilizes a solid-state camera, and in order to prevent noises from being superimposed upon the signal fed to an image display, a transmission line which transmits a high frequency current to the diathermic cutter or a transmission line which transmits an ultrasonic signal to or receives an ultrasonic signal from an ultrasonic probe is shielded by a conductor member. In particular, for a transmission line which conveys the high frequency current, impedance regulating means is connected therewith in order to prevent the high frequency current from leaking through a distributed capacitance between the transmission line and the conductor member. Alternatively, a narrow bandpass filter may be provided which limits the frequency band of the high frequency current. A coaxial cable may be used in which both the transmission line and the conductor member are formed of conductive rubber.

Some Effects of Finite Sample Size and Persistence on Meteorological Statistics.Part II: Potential Predictability

Abstract: Potential predictability of a meteorological time series can be estimated from the ratio of the actual interannual variability to the natural variability associated with climatic noise. The extent to which this ratio is larger than one is taken as a measure of the climatic signal-to-noise variance ratio. However, there are major problems in separating out the signal from the noise which are compounded by persistence in the time series, the presence of an annual cycle and the effects of finite sample size. An F test may be used to deduce that a signal is present by rejecting the null hypothesis of no signal. However, it is shown that, generally, the null hypothesis should not be accepted just because it cannot be rejected. Confidence limits can be very large when a signal is present in a finite sample since the signal will be fictitiously correlated with the noise due to sampling in a manner that is unknown. Although the correlation coefficient is statistically not significant, there is a large im...

Noise reduction system for video signals

Abstract: Noise reduction on a video signal is achieved by an adaptive filter system which is capable of automatic changes in filter parameters. This inventive concept includes an automatic method of independently changing both the width and center frequency of the teeth of a comb type bandpass envelope of the filter, as well as adjusting the amplitude response of the filter, independent of the bandpass characteristics, in order to closely match the filter bandpass response to the power spectrum of the video signal being processed, thus rejecting noise in those portions of the spectrum not being used by the video signal. The filter system herein disclosed also provides an adaptive spatial processing of the video signal thus further improving said signal by enhancing detail in the image and by smoothing low amplitude noise in relatively detail free areas of the picture.

Combined homomorphic and local-statistics processing for restoration of images degraded by signal-dependent noise.

Abstract: The generalized homomorphic transformation to make signal-dependent noise independent of the signal is combined with a local-statistics image restoration technique to process images degraded by signal-dependent noise. Experimental results are given for images degraded by film-grain noise and by multiplicative noise.

Laser Doppler flow monitor

Abstract: A method and apparatus for measuring the velocity of moving particles such as red blood cells in a tissue sample is disclosed, characterized by digital processing techniques and autocorrelation. The moving particles are illuminated to produce a spread spectrum optical signal resulting from the Doppler shift occurring when photons are scattered by the moving particles. A spread spectrum electrical signal corresponding with the optical signal and containing spectral and noise components is generated from the optical signal. The electrical signal is filtered to produce the bandpass and DC signals which are subsequently converted to digital form. A first autocorrelation function is calculated from the bandpass signal and a noise autocorrelation function is determined in accordance with the DC signal level. The first and noise autocorrelation functions are compared to produce an autocorrelation function free of a noise component. From the autocorrelation function, the mean frequency of the electrical signal is linearly calculated, the mean frequency corresponding with the average velocity of the moving particles.

On errors of fit and accuracy in matching synthetic seismograms and seismic traces

Abstract: A synthetic seismogram that closely resembles a seismic trace recorded at a well may not be at all reliable for, say, stratigraphic interpretation around the well. The most accurate synthetic seismogram is, in general, not the one that displays the smallest errors of fit to the trace but the one that best estimates the noise on the trace. If the match is confined to a short interval of interest or if the seismic reflection wavelet is allowed to be unduly long, there is considerable danger of forcing a spurious fit that treats the noise on the trace as part of the seismic reflection signal instead of making a genuine match with the signal itself. This paper outlines tests that allow an objective and quantitative evaluation of the accuracy of any match and illustrates their application with practical examples. The accuracy of estimation is summarized by the normalized mean square error (NMSE) in the estimated reflection signal, which is shown to be (/n)(PN/PS) where PS/PN is the signal-to-noise power ratio and n is the spectral smoothing factor. That is, the accuracy varies directly with the ratio of the power in the signal (taken to be the synthetic) to that in the noise on the seismic trace, and the smoothing acts to improve the accuracy of the predicted signal. The construction of confidence intervals for the NMSE is discussed. Guidelines for the choice of the spectral smoothing factor n are given. The variation of wavelet shape due to different realizations of the noise component is illustrated, and the use of confidence intervals on wavelet phase is recommended. Tests are described for examining the normality and stationarity of the errors of fit and their independence of the estimated reflection signal.

Image processing method using a collapsed walsh-hadamard transform

Abstract: An improved image processing method uses a modified Walsh-Hadamard transform to remove noise and preserve image structure in a sampled image. Image signals representative of the light value of elements of the image are grouped into signal arrays corresponding to blocks of image elements. These signals are mapped into larger signal arrays such that one or more image signals appear two or more times in each larger array. The larger arrays are transformed by Walsh-Hadamard combinations characteristic of the larger array into sets of coefficient signals. Noise is reduced by modifying--i.e., coring or clipping--and inverting selected coefficient signals so as to recover processed signals--less noise--representative of each smaller signal array. The results exhibit acceptable rendition of low contrast detail while at the same time reducing certain processing artifacts characteristic of the unimproved Walsh-Hadamard block transform.

Signal to noise in derived NMR images.

Abstract: The NMR image is dependent on multiple tissue parameters: hydrogen density, relaxation times T1 and T2, and flow. From the acquired intensity images, T1, T2, and hydrogen images may be produced. The signal/noise of these derived images is critically dependent on the choice of acquisition parameters. Using the calculated T1, T2, and hydrogen images, intensity images may be calculated at arbitrary values of TE and TR, some of which (for example, short TE or TR) may be physically unacquirable.

Synchronous phase marker and amplitude detector

Abstract: Disclosed is an electronic circuit for determining the phase difference between an input signal and a reference signal where both signals are of the same frequency. Furthermore, the circuit provides an amplitude output indicative of the input signal even when that signal is obscured by noise. A chopper is supplied with the obscured signal input and a reference signal input and provides an output to an integrator which provides a control voltage for a voltage controlled phase shifter which supplies an out of phase input to the chopper. The input to the voltage controlled phase shifter is of the same frequency as the signal obscured by noise. A further output of the voltage controlled phase shifter is 90° out of phase with respect to the reference supplied to the chopper and thus is in phase with the signal obscured by noise and provides the desired marker output. This marker output is also supplied as a reference to a second chopper which is also supplied with the obscured signal as an input. The output of the second chopper after suitable amplification, is proportional to the amplitude of the signal that is buried in noise. Thus, as long as the frequency of the signal buried in noise is known and supplied in the form of a reference signal, the phase and amplitude of the signal can be determined with the synchronous phase marker and amplitude detector.

The implementation of digital filters using a modified Widrow-Hoff algorithm for the adaptive cancellation of acoustic noise

Abstract: The active reduction of noise is an application of the principle of superposition in which an unwanted noise signal is detected by a microphone and processed by an electronic controller to produce an equal amplitude, 180° out-of-phase cancellation signal. The signal is then appropriately amplified and injected back into the space by a loudspeaker. This paper describes an electronic controller based on a digital implementation of transversal filters using a modification of the Widrow-Hoff Least-Mean-Squared Algorithm. In the case of active noise reduction there is no signal to enhance and all of the detected input must be cancelled. Further, the time required for the physical acoustic wave must be taken into consideration for the system to work.

Coded modulation system with feedback

Abstract: A receiver for use in deciding which signal points were sent from a transmitter based on corresponding noise affected signals received over a channel, the transmitter including an encoder which encodes a stream of information symbols into the signal points, the noise affected signals carrying information about a particular sequence of possible states occupied in a succession of time intervals by a finite state process. The receiver includes feedback circuitry for generating a plurality of different modified versions of each received signal, and a decoder for deciding which signal points were sent, given the received signals, based on estimating the particular sequence of states, and using at least two different modified versions.

A system for reducing the noise in a television signal

Abstract: The amount of noise reduction of a television signal produced by averaging corresponding pixels from one frame to the next is reduced by a correction factor when motion in the picture is detected. In order to prevent very active motion from disturbing detection of the noise level, a noise level measurement signal is subjected to a hold of its value in a time briefly preceding a highly active motion in the picture until a time shortly after the end of such highly active motion. The motion signal is processed so as to provide such a hold only when motion is highly active in the picture, and that signal is prolonged in a further circuit so that it will have a duration long enough to cover build-up of that motion and its trailing off, when the noise measurement signal is delayed by about half of the prolongation, so that the noise measurement level that is held corresponds to the noise level prior to the buildup of the motion which shortly thereafter becomes highly active. The noise value thus held controls the size of the correction factor (k) produced by the presence of the motion signal.

Acoustic detection of tool break events in machine tool operations

Abstract: A system and method for monitoring vibrations of a cutting tool produced by tool break events, and for interpreting them to detect tool breaks of sufficient magnitude to endanger the machined part. The signal generated by a sensor such as an accelerometer is preprocessed to attenuate low frequency machining noise and detect the energy in a higher frequency band, then sampled, and the digitized signal samples analyzed by tool break detection logic. This logic is triggered by a positive-going signal transient, and prevents false alarms on minor tool break events that do not mar the workpiece and on noise from other sources.

Large-memory real-time multichannel multiplexed pattern recognition

Abstract: The principle and experimental design of a real-time multichannel multiplexed optical pattern recognition system via use of a 25-focus dichromated gelatin holographic lens (hololens) are described. Each of the 25 foci of the hololens may have a storage and matched filtering capability approaching that of a single-lens correlator. If the space-bandwidth product of an input image is limited, as is true in most practical cases, the 25-focus hololens system has 25 times the capability of a single lens. Experimental results have shown that the interfilter noise is not serious. The system has already demonstrated the storage and recognition of over 70 matched filters - which is a larger capacity than any optical pattern recognition system reported to date.

Acoustic monitoring of cutting conditions to detect tool break events

Abstract: This tool break detection system relies on monitoring changes in the cutting noise itself, rather than detecting the tool fracture acoustic signal. A broken tool capable of damaging the workpiece is detected, and tool break events that do not affect cutting conditions are ignored. The signal from a sensor such as an accelerometer is preprocessed to attenuate low frequency machinery noise and detect the signal energy in a band below 100 KHz, then sampled, and the digitized signal samples analyzed by pattern recognition logic. Runout false alarms during rough surface cutting are prevented; after detection of an abrupt increase or decrease in signal level, the confirmation period to test for a persistent shift in mean level is set longer than the workpiece revolution period.

Multiple measurement noise reducing system using artifact edge identification and selective signal processing

Abstract: Disclosed is a multiple measurement multiple energy x-ray imaging system in which a plurality of measurements are processed to provide a first image signal representing a desired parameter of an object and in which the plurality of measurements are processed to provide a second processed image signal having greater signal-to-noise ratio than the first processed image signal but in which extraneous arti­ facts may be introduced into the signal. The spatial location of the edges of the extraneous artifacts are determined. The first processed image signal and the second processed image signal are combined to provide an improved image signal except at the spatial locations of the extraneous artifacts where the first processed image signal is used for the image signal thereby eliminating the extraneous artifact from the displayed image.

Multiple measurement noise reducing system using space-variant filters

Abstract: Extraneous signals or artifacts are reduced in a multiple measurement noise reducing system such as an X-ray imaging system by processing a plurality of measurements to obtain a first image signal of an object representing a desired parameter such as a blood vessel, processing the plurality of measurements to provide a second image signal having increased signal-to-noise, low pass filtering the first image signal, high pass filtering the second image signal, and then combining the two filtered signals. The filter frequencies are varied in response to the presence of artifacts to minimize effects of the artifact on the combined signal.

Solid-state imaging apparatus

Abstract: This invention relates to a solid-state imaging apparatus wherein photo signals are read out through MOS type FETs from photosensors, such as photodiodes, arrayed in two dimensions in large numbers. The invention improves the signal-to-noise ratio of the output signal by reducing or eliminating noise components mixed in the photo signal. Analysis of the noise components has revealed a correlation in which a noise component of a certain polarity develops again with the opposite polarity after a period that is shorter than one horizontal scanning period by the duration of one horizontal scanning pulse. To take advantage of this correlation, the apparatus provides a processing circuit that includes a delay circuit and an adder circuit to act together to cancel the noise.

Acoustic tool break detection system and method

Abstract: Substantial cutting condition changes that occur gradually, as opposed to the more usual sudden large change, are detected by setting upper and lower cutting noise mean level thresholds. When the mean cutting noise exceeds the upper threshold or stays below the lower threshold for a preset number of signal samples, a tool break alarm is generated. Techniques are given to reduce false alarms at the start and end of the cut and on runout on initial rough surface cuts. The system comprises an accelerometer or other sensor whose signal is preprocessed to attenuate lower frequency machinery noise and detect the signal energy in a band below 100 KHz, then sampled, and the digitized signal samples analyzed by pattern recognition logic.

Apparatus and method to increase dynamic range of digital measurements

Abstract: Disclosed is a method for overcoming one of the limiting factors in applying digital techniques to measuring analog signals over a wide dynamic range, namely, the uncertainty introduced into the measurement by noise and A/D conversion, particularly at low signal levels. A central feature of the technique is the filtering of the signal with a variable time constant digital filter, the time constant being a function of the measured signal in such way as to increase the effective resolution of small signals at the expense of an increased transient delay. For large signals, the time constant is reduced so that adequate transient response is provided when it is most needed and when there is already adequate resolution.

Characterization and Measurement of Radiometer Stability

Abstract: For the characterization of radiometer noise and stability a new and very practical method is introduced. It consists of the measurement of the "Allan-variance" well known for the characterization of the stability of frequency standards. The plot of the Allan variance versus integration time allows one to determine the different types of fluctuations of the radio-meter output signal. In particular, the best range of integration time for optimum use of the system can accurately be evaluated. Theoretical considerations and experimental results are presented.