Showing papers on "Noise (signal processing) published in 1979"

Multiple emitter location and signal Parameter estimation

Abstract: Processing the signals received on an array of sensors for the location of the emitter is of great enough interest to have been treated under many special case assumptions. The general problem considers sensors with arbitrary locations and arbitrary directional characteristics (gain/phase/polarization) in a noise/interference environment of arbitrary covariance matrix. This report is concerned first with the multiple emitter aspect of this problem and second with the generality of solution. A description is given of the multiple signal classification (MUSIC) algorithm, which provides asymptotically unbiased estimates of 1) number of incident wavefronts present; 2) directions of arrival (DOA) (or emitter locations); 3) strengths and cross correlations among the incident waveforms; 4) noise/interference strength. Examples and comparisons with methods based on maximum likelihood (ML) and maximum entropy (ME), as well as conventional beamforming are included. An example of its use as a multiple frequency estimator operating on time series is included.

An introduction to statistical signal processing with applications

Abstract: 1 Introduction 2 Signals and Systems 3 Detection Theory 4 Detection of Signals in Noise 5 Estimation Theory 6 Estimation of Waveforms 7 Further Topics in Detection and Estimation 8 Applications to Communication and Radar Systems 9 Miscellaneous Applications Appendix A: Bilateral Transforms Appendix B: Calculus of Extrema Appendix C: Vectors and Matrices Subject Index Author Index

A spectral subtraction algorithm for suppression of acoustic noise in speech

Abstract: Spectral subtraction has been shown to be an effective approach for reducing ambient acoustic noise in order to improve the intelligibility and quality of digitally compressed speech. This paper presents a set of implementation specifications to improve algorithm performance and minimize algorithm computation and memory requirements. It is shown spectral subtraction can be implemented in terms of a nonstationary, multiplicative, frequency domain filter which changes with the time varying spectral characteristics of the speech. Using this filter a speech activity detector is defined and used to allow the algorithm to adapt automatically to changing ambient noise environments. Also the bandwidth information of this filter is used to further reduce the residual narrowband noise components which remain after spectral subtraction.

A Central Limit Theorem for Parameter Estimation in Stationary Vector Time Series and its Application to Models for a Signal Observed with Noise

Abstract: A general finite parameter model for stationary ergodic nondeterministic vector time series is considered. A central limit theorem for parameter estimates, obtained by maximising frequency domain approximations to the Gaussian likelihood, is established. The treatment given extends the central limit theorem of Dunsmuir and Hannan in that the innovations covariance matrix and the linear transfer function need not be separately parameterised. Models for a stationary vector signal observed with stationary vector noise are discussed in relation to the central limit theorem and the conditions imposed for this result are related to this model. Finally, the special case of a scalar autoregressive signal observed with noise is discussed. It is shown that this model may be reparameterised so that the central limit theorem of Dunsmuir and Hannan may be applied.

The Spectra of Fault-Induced Transients

Abstract: During the first cycle or two following a power system fault, a high-speed protective relay is expected to make a decision as to the severity or location of the fault, usually based on 60 Hz information, i.e. the phase and magnitude of 60 Hz voltage or current signals. It is precisely at this time however that the signal is badly corrupted by noise, in the form of a dc offset or frequencies above 60 Hz.

Maximum-likelihood spectral estimation

Abstract: A description has been given of some signal processing methods in large array seismology. The optimum detector for a known signal in additive Gaussian noise was shown to consist of the tandem combination of appropriate time delays, maximum-likelihood filter, noise whitening filter, matched filter, and a threshold comparator. The maximum-likelihood filter plays an important role in determining the structure of the optimum detector. This filter also provides a minimum-variance unbiased estimate for the input signal when it is not known, which is the same as the maximum-likelihood estimate of the signal if we have Gaussian noise.

Noise reducing system

Abstract: A noise reducer wherein, depending upon the magnitude of a difference signal between an input television signal at the present time and a television signal recorded in a frame memory and with noise reduced, the mixing ratio between the present-time input signal and the television signal obtained from the frame memory is varied, and a part of the mixed signal is applied to the frame memory while the other part is used as a television signal with noise reduced; a noise reducing system wherein, in order to make the reduction of noise possible even for a moving object, a movement of a picture in one frame time is detected, the output of the frame memory is compensated for with the movement, and depending upon the magnitude of a difference signal between the present-time input television signal and the movement compensated output signal of the frame memory, the mixing ratio between the present-time input television signal and the compensated output signal of the frame memory is varied.

Borehole acoustic telemetry system synchronous detector

Abstract: In a borehole telemetry system for acoustically transmitting data over a pipe suspended in a borehole, the level of noise in the data stream is inherently high, making the use of discrete frequencies advantageous to provide useful data. Any drift in electrical circuits which might affect or be affected by the use of precise frequencies is undesirable. A synchronous detector facilitates the removal of noise components from the data stream by comparing in a commutative filter the phase difference between a switching signal taken from the incoming data signal path, after the second stage of commutative filtering, with the data signal emerging from the last stage of filtering. The synchronous detector also compares a data signal having two stages of filtering with another data signal having six stages of filtering with the additional filtering, causing a phase shift in frequencies outside the precise frequency window, which the synchronous detector also rejects.

Detection of hidden periodicities by adaptive extrapolation

Abstract: A method is presented for determining the harmonic components of a noisy signal by nonlinear extrapolation beyond the data interval. The method is based on an algorithm that adaptively reduces the spectral components due to noise.

Kinetic theory for fluctuations and noise in computer simulation of plasma

Abstract: An accurate theory of fluctuations and noise in computer simulation of plasma is developed The analytic method describes the space and time discretization exactly and the results reduce simply and correctly to the standard results of plasma kinetic theory in the limit of small space and time step If the particles are imagined to be a Monte‐Carlo sampling of the phase space, then the fluctuations in this sampling, as modified by collective effects, are a concern of this paper This theory is of interest in theoretical and empirical studies to understand the character of representation by simulation methods of plasma processes such as transport

Predictive speech signal coding with reduced noise effects

Abstract: A predictive speech signal processor features an adaptive filter in a feedback network around the quantizer. The adaptive filter essentially combines the quantizing error signal, the formant related prediction parameter signals and the difference signal to concentrate the quantizing error noise in spectral peaks corresponding to the time-varying formant portions of the speech spectrum so that the quantizing noise is masked by the speech signal formants.

Electronics noise reducing apparatus and method

Abstract: The present disclosure teaches a method and apparatus for reducing noise in an electronic signal. These inventive conceptions include a means for delaying the electronic signal and a comparison means for comparing the delayed signal to the signal in its undelayed condition. Means are provided for processing the signal in response to the comparison means to remove at least part of the noise.

General Analysis of Fringe Contrast in Electronic Speckle Pattern Interferometry

Abstract: A general analysis of signal processing in electronic speckle pattern interferometry is presented. The effects of limited T.V.-camera resolution is included, and it is shown that the T.V.-monitor brightness is given by essentially the same expression as for full T.V.-camera resolution. One term in this expression is the fringe signal, while the others represent noise. The optimal reference-to-object intensity ratio, which maximizes the fringe signal, is determined and the dependence on the size of the aperture is given. The effect of a double slit aperture is compared with the effect of a circular aperture.

Accuracy of QRS detection in relation to the analysis of high-frequency components in the electrocardiogram.

Abstract: The detection of high-frequency components in the QRS complex by means of coherent signal averaging is affected by inaccuracy in the time reference. Jitter of the time reference or trigger, which is derived from the low-frequency QRS complex, will be caused by the noise in the QRS complex. A theory is developed by which the trigger jitter can be predicted from the properties of signal and noise for a system consisting of a filter and a single-level, dual-level or peak detector. The theory is applicable when the noise is additive and, under certain conditions, also when the noise is multiplicative. Using this theory the trigger jitter of a given filter-level detection system is compared with that of an optimal detection system consisting of a matched filter and peak detector. The theoretical trigger jitter of the above-mentioned detectors has been computer for e.c.g. recordings of 23 individuals, as a function of different filter settings and and with the assumption that the noise was additive. This resulted in an average trigger jitter of 0·2±0·1 ms for the optimal system, while for the peak detector and the dual level detector the jitter was slightly higher provided that the QRS complexes were symmetrical after filtering. With the effects of ventilation taken into account (multiplicative noise) it is shown that dual-level detection is considerably more accurate than single-level detection. A description of the dual-level detector is also presented.

Image detail improvement in a vertical detail enhancement system

Abstract: In a color television receiver including a comb filter for separating luminance and chrominance components of a color television signal, a network is included for enhancing vertical image detail to enhance vertical resolution in the luminance content of a displayed image. The comb filter provides a combed luminance signal output from which vertical detail signal information has been unavoidably deleted, and a combed chrominance signal output including signal frequency components representative of the deleted detail signal, which are selectively extracted from the combed chrominance signal. Low level detail signals are restored to the combed luminance signal via a first signal processing network which exhibits a prescribed signal restoration gain. The detail signal is also added to the combed luminance signal via a second network which cores (removes) low level detail signals including noise in a first operating mode, and amplifies higher level detail signals to enhance vertical image definition in a second mode. Rapid transitions from the coring to the enhancement mode are undesirably manifested in a displayed diagonal image as serrations along the edge of the diagonal line. The visible effects of the serrations are reduced to an acceptable minimum by low pass filtering the enhanced cored detail signal before being added to the combed luminance signal.

Image enhancement by stochastic homomorphic filtering

Abstract: The problem of image enhancement by nonlinear two-dimensional (2-D) homomorphic filtering is approached using stochastic models of the signal and degradations. Homomorphic filtering has been previously used for image enhancement, but the linear filtering operation has generally been chosen heuristically. In this paper stochastic image models previously described and analyzed by the authors are used to model the true image and interfering components (shadows and salt-and-pepper noise). The problem of designing the linear filter can then be formulated as one of linear least mean-squared error (Wiener) filtering. Examples of processing of typical real-world images are included to indicate the obtainable results.

Maximum likelihood parameter estimation of noisy data

Abstract: For most signal models of interest, Maximum Likelihood (ML) parameter estimation in the presence of noise is a difficult, non-linear problem. A new iterative algorithm has been developed for ML estimation, however, which effectively decouples the uncertainty in the signal and parameter values, thus simplifying the calculation required. It can be shown that the likelihood function increases on each iteration of the algorithm. When applied to a particular pole-zero (ARMA) signal model, each pass consists of a linear smoothing filter followed by solving a set of linear equations for both the pole and zero polynomial coefficients.

Noise reduction system for video signals

Abstract: A recursive noise reduction system for a television system uses the spatial correlation in a frame difference signal derived by element-by-element subtraction of an incoming video signal from corresponding picture elements of a relatively noise-free stored video signal to redue noise in a video signal. The spatial correlation is used to suppress the components of the frame difference signal which are due to frame-to-frame changes in the video resulting from motion in the scene, thus producing a signal which contains substantially only the noise in the incoming video. The noise signal thus derived is subtracted from the incoming video signal to produce a noise-reduced output signal for display or recording. The noise-reduced output signal and the incoming video are added together in varying proportions according to the amount of scene-to-scene motion detected and the sum is stored for use in subsequent treatment of new incoming video.

Multiple correlator reference processor

Abstract: A signal processor for use with an array of antenna elements comprises a plurality of pairs of receiver channels which receive signals from respective halves of the array. The component of the signals resulting from noise, such as the noise generated within the ocean, is substantially decorrelated between the respective halves of the array, while a component of the signal obtained from a source of a desired signal is coherent between the two halves of the array. The signals in each pair of channels are translated to intermediate frequencies by mixing the signals with reference signals of differing frequencies in each of the respective pairs of channels. The translated signals in each pair of channels are then multiplied together to produce a signal of substantially constant amplitude which is suitable for detection, or for a bearing deviation indication. Output signals of the respective multipliers are summed together and passed through a low pass filter having a pass band approximately equal to the reciprocal of the anticipated dwell time of the signal source within the beam width of the array of antenna elements. The uncorrelated noise results in an alternating component in the products of the respective multipliers which are substantially cancelled in the summing and filtering to produce a higher signal-to-noise ratio.

Self-calibrated subcarrier telemetry system

Abstract: A self-calibrating subcarrier telemetry system for measuring strain on rotating members of a turbine under operating conditions. A rotor mounted portion of the system includes a strain gage transducer bridge excited by a subcarrier alternating current derived from an induced power source. The transducer bridge produces an output signal, amplitude modulated by the strain signal whereby the modulation shifts the strain signal into a higher frequency portion of the spectrum away from low-frequency noise related to the rotational speed of the turbine. A calibration signal is introduced by automatically unbalancing the bridge transducer periodically at a rate related to the subcarrier frequency. The strain signal is recovered in a stationary data reception portion of the system by a synchronous detector. A reference calibration signal is provided against which receiver gain is adjusted to achieve a null, leaving only the calibrated strain signal and achieving indpendence of variations in system gain. Nulling against the unipolar calibration reference further provides a means to distinguish tensile and compressive strain.

Borehole acoustic telemetry system

Abstract: In a borehole acoustic telemetry system for acoustically transmitting data over a pipe suspended in a borehole, the level of noise in the data stream is inherently high, making the use of precise frequencies advantageous to provide useful data. A first transmitter in the system operates at a precise frequency to transmit a signal over the pipe where it is received by a receive and retransmit circuit path. Components in the receive and retransmit section filter and amplify a data component of the signal and retransmit the data signal at a precise frequency. Crystal controlled oscillator clocks are operated in the system at a same frequency in the transmitter and receiver-retransmitter to insure precise frequency control of the system.

Incoherent image addition and subtraction: a technique.

Abstract: A technique of incoherent image addition and subtraction is described. The basic advantage of this technique is its use of white light processing, in which case the unavoidable artifact noise in the coherent optical processor may be removed. Although the incoherent processing technique that we have proposed is effective only in a 1-D operation, it also works for 2-D image addition and subtraction.

Picture Processing and Digital Filtering

Abstract: Two-Dimensional transforms.- Two-dimensional nonrecursive filters.- Two-dimensional recursive filtering.- Image enhancement and restoration.- Noise considerations in digital image processing hardware.- Recent advances in picture processing and digital filtering.

Digital input apparatus

Abstract: A digital input apparatus is provided which is used as an input apparatus for a digital signal processor and can eliminate noise components resulting from electromagnetic induction and resulting from chattering which is produced by the opening or closing of a contact. One input signal outputted from the multiplexer (105) is applied through a latch flip-flop (108) to a counter (114) used on a time sharing basis so that counting is effected. Individual counts corresponding to a plurality of input signals are stored in a memory (117). When a count becomes all "1's" or "0's", the counter (114) produces a carry signal or a borrow signal supplied to a J-K flip-flop (113). The J-K flip-flop (113) produces an input signal of a predetermined waveform free from noise components.

Method and apparatus for flow velocity determination

Abstract: A method of determining flow velocities by measuring the phase difference between Doppler signals derived from wave pulses and reflected by substantially the same reflector at two different times, the interval between the times being predetermined, a pair of electric signals being derived according to the method from each Doppler signal by modulation in quadrature, the signals jointly bearing information relating to the phase of the Doppler signal, and a device for performing the method. In order to make full use of the possible measuring range, even at a relatively poor signal/noise ratio, at least a first and a second pair of signals are combined to form a third pair of electric signals which together bear an item of information depending on the phase difference between the Doppler signals. Mean-value signals are formed, each corresponding to the mean value of one of the third pair of signals, and an output signal which corresponds to the mean value of the phase difference between the Doppler signals is derived from the mean-value signals. It is particularly advantageous to use the method in an ultrasound diagnostic device for determining the velocity profile of a flow, more particularly of blood in a blood vessel.

System for reducing or suppressing noise components in television signal

Abstract: A system for reducing or suppressing the noise components in the TV signal wherein the component representative of the difference between the as-input (or as-received) TV signal and the TV signal which has been delayed by one horizontal scanning period is derived, the difference component is subjected to the amplitude limitation, and the noise components in the TV signal reproduced by VTR or the like are removed or suppressed by a comb filter comprising said as-input TV signal and the amplitude-limited difference component.

Intermodulation distortion test

Abstract: Errors in test results are minimized in a test system (FIG. 1) employing digital data acquisition units (121) when measuring intermodulation distortion of a voice frequency communication facility (105) by employing a unique 3-tone test signal. To this end, the three tones have predetermined amplitude, frequency and phase relationships to obtain a test signal having a desired optimum probability density function which is substantially Gaussian. Additionally, circuit noise components are eliminated from the test results by obtaining a measure of noise with a single tone test signal and subtracting it out from the three tone test results. In a specific embodiment, a measure of the power spectrum resulting from the three tone signal and the power spectrum of the single tone signal are obtained, combined and utilized to obtain measurements of second and third order intermodulation distortion products compensated for noise.

Method and arrangement for measuring the physical temperature of an object by means of microwaves

Abstract: A method for measuring the physical temperature of objects by means of microwaves using a Dicke radiometer. A noise signal is continuously applied to an antenna which is directed towards the object and is periodically and alternately applied, together with the antenna signal, which includes reflected noise and object emission to the radiometer. The integrated output signal of the radiometer controls the noise power and is proportional to the object temperature.

Conjoint effect of physical stress and noise stress on information processing performance and cardiac response.

Abstract: The conjoint effect of physical stress, induced by requiring subjects to run a treadmill, and 90 dB white noise stress was evaluated on information processing performance using a delayed digit recall subsidiary task measure and cardiac response. As anticipated, physical stress significantly raised heart rate, and noise stress significantly degraded information processing ability. The experiment failed to demonstrate a linearly additive relationship between noise and physical stress on either cardiac response or information processing performance.