Showing papers on "Noise (signal processing) published in 1974"

Image Processing In Signal-Dependent Noise

Abstract: Image detection noise is a fundamental limitation in picture processing, whether analog or digital. This noise is characteristically signal-dependent and this signal-dependence introduces significant problems in the design of appropriate noise-suppression techniques. This paper outlines some recent results obtained by the authors in the optimum suppression of two types of signal-dependent image noise: film-grain noise and photoelectron shot noise. The work in grain noise suppression involves deriving the minimum-mean-square error Wiener filter for a new form of signal-dependent noise model suggested in earlier work by T. S. Huang. Implementation of these filters by either coherent optical or digital processing techniques is possible. Digital computer simulations of grain noise suppression using two particular cases of this additive, "signal-modulated" noise model were performed. They demonstrate the potential advantages of noise suppression filters which make use of a priori knowledge of the signal-dependent nature of the grain noise. The results of work on linear, unbiased restoration of images recorded in the presence of photoelectron noise are summarized. Additional work in both of these areas is suggested, with a particular need existing for correlating the properties of various models proposed for grain noise with experimental data obtained on emulsions using scanning microdensitome ters.

Detector array fixed-pattern noise compensation

Abstract: Fixed pattern noise compensation is provided for an array of detectors by premeasuring output signals of the detectors under a low (preferably at virtually absolute zero) level of uniform incident energy, converting the measured signal level of each detector to digital signals, and storing the digital signals in a memory for reading out in synchronism with scanning outputs of the detectors during normal system operation. The digital compensation signals are converted to analog form and subtracted from the output signals of the respective detectors during each successive scan cycle of the system operation. To eliminate error from random noise, several noise measurements may be averaged to produce the fixed pattern noise compensation signals.

Method and apparatus for reducing noise content in audio signals

Abstract: Unwanted background noise in audio signals, and particularly in musical material, is significantly reduced by a multiple band dynamic filtering system operated in response to the fundamental and harmonic content and degree of correlation or nonrandomness of the audio signal. A plurality of voltage controlled band-pass gates or filters are established in the audio signal path for individually and selectively passing frequency content of the audio signal falling within each frequency band. The fundamental and harmonic content of the signal, typically a musical composition, is detected by a corresponding plurality of band-pass signal detectors, the outputs of which are connected to and for operating associated band-pass gates. Normally the band-pass gates are closed blocking any background noise present on the incoming signal. The band-pass detectors sense the presence of any fundamental or harmonic signal content and cause the appropriate band-pass gates to open and pass the full frequency content of the musical signal. The degree of correlation or nonrandomness of the audio signal is automatically monitored and the threshold detection of the presence of signal content in any one of the given frequency bands is varied in accordance with the degree of signal correlation.

Computer interface system

Abstract: An interface logic circuit permitting the transfer of information between two computers having asynchronous clocks is disclosed. The information transfer involves utilization of control signals (including request, return-response, ready) to generate properly timed data strobe signals. Noise problems are avoided because each control signal, upon receipt, is verified by at least two clock pulses at the receiving computer. If control signals are verified, a data strobe pulse is generated to accomplish a data transfer. Once initiated the data strobe signal is properly completed independently of signal disturbances in the control signal initiating the data strobe signal. Completion of the data strobe signal is announced by automatic turn-off of a return-response control signal.

Quantitative Effects of Stationary Linear Image Processing on Noise and Resolution of Structure in Radionuclide Images

Abstract: Processing radionuclide image data in an attempt to improve its diagnostic usefulness inevitably changes both the noise and the resolution of structures in the image. Although at present little conclusive evidence exists to indicate whether or not image processing is beneficial, an understanding of the quantitative effects of various processing techniques on parameters of resolution, noise magnitude, and noise texture seems to provide a useful beginning towards solution of the more difficult problem of understanding the effects of image processing on diagnostic image quality. Quantitative effects of stationary linear image processing procedures, which include all convolutions and filtering operations, can be predicted rather simply. In the present work, expressions for predicting these quantitative effects are developed and are applied to computer-synthesized image data to provide illustrative examples of the effects of typical noise-smoothing and resolutionenhancing operations. (auth)

Method of and apparatus for aiding hearing and the like

Abstract: This disclosure deals with electronically aiding sensori-neural deafness with frequency-segmented, dynamic range-compressed speech signal processing, wherein noise vs. speech signal discrimination is employed with an optional semi-remote microphone input, and with an optional electronic frequency-shift processing of the signal to prevent or reduce oscillation due to acoustic airborne and/or vibrational feedback between the earphone(s) and the microphone(s).

Real-time cross-correlation signal processor

Abstract: Apparatus for improving the signal to noise ratio in an electrical signal. A signal enhancement processor operating in real time and selecting signals based upon the similarity of the incoming signal to a locally generated reference and which does not require that signals be filterable in the frequency domain, that external reference signals be supplied, or that signal amplitude criteria be employed. A system for providing input signal attenuation or rejection as a function of the frequency or phase of the input signal, with attenuation at a maximum for an undesired signal and at a minimum for a desired signal.

Phase comparison systems employing improved phaselock loop apparatus

Abstract: A high-accuracy phase comparison system for noise-contaminated fixed-frequency input signals, such as Omega radionavigation signals, employs a pair of phaselock loops in which output pulses from a high-frequency oscillator are deleted at the frequency of a variable-frequency oscillator which is responsive to the detected phase difference between the associated input signal and an associated reference signal, thereby to provide a high-frequency intermediate signal which is frequency-divided to produce the reference signal continuously and free of noise. The relative phase of the input signals may be determined by phase-comparing the reference signals of the two phaselock loops or, to provide even higher precision, by phase-comparing the variable-frequency signals of the two loops.

Threshold correction system in FSK transmissions

Abstract: A demodulator produces mark and space signals in response to mark and tone signals received from a radio receiver. The signals after detection are in the form of characteristic tones and are separated by corresponding band pass filters. After separation, AM detection of the mark and space signals is accomplished in envelope detectors whose output voltages are D.C. voltages. In the absence of noise, the detector voltages are essentially a rounded off version of the binary signal (mark) and a rounded off version of the complement (space) of the binary signal. These voltages are compared and their difference, a binary signal, after filtering is applied to a system which automatically computes a mark-space decision threshold for a comparator or slicer such that the slicer produces a mark output when the filtered output is above the threshold and a space output when the signal is below the threshold to achieve optimum detection of the mark-space data during fading of either one or both of the carrier waves on which such data is transmitted to the radio receiver. The optimum decision threshold is computed from the signal peaks which are stored in two peak detectors, one for the positive peak and one for the negative peak. The peak detectors are periodically discharged to allow a fresh peak to be stored and the discharge circuits obtain their cues from state changes observed at the slicer output. Hence the decisions themselves signal the timing of the discharge of the peak detectors. A delay network ensures that the charge stored by each peak detector is not caused by noise; and also a sequencing logic circuit prevents the same detector from being discharged twice in a row thereby providing additional immunity to noise.

On optimization of cascade fixed-point digital filters

Abstract: The generation of roundoff accumulation noise in implementing a cascade digital filter can be regarded as a multistage process; therefore, the minimum-noise realization is obtained by dynamic programming. The effect of scaling on the noises is discussed by a numerical example.

Interferences in Phase-Locked Loops

Abstract: An analysis of the behavior of a second-order phase-locked loop is presented when an unwanted signal is added to the useful signal. Both signals are sinusoidal and unmodulated, and the analysis is made in the absence of additive noise. When the loop remains locked on the useful signal, a parasitic signal exists at the phase detector output. This signal produces a parasitic phase modulation of the VCO and a static phase error in the loop. The parasitic signal amplitude, the parasitic phase modulation index, and the static phase error are calculated. A necessary condition for the loop to remain in lock is derived. When the loop is initially unlocked, locking can occur either on the useful signal or on the unwanted signal, depending on the amplitude ratio and the frequency difference of the two signals. A formula allowing one to compute the pull-in time is obtained. When the loop locks on the useful signal, acquisition can be slower or faster than in the absence of an unwanted signal. The same phenomenon is observed when the loop locks on the unwanted signal.

Computer-controlled monitoring and data reduction for multiple ion-selective electrodes in a flowing system

Abstract: : Analog and digital instrumentation have been developed for computer-controlled monitoring of multiple ion-selective electrodes in a flowing stream. Analog features include wide bandpass, low drift, and low noise, while the digital system features include multiplexing, signal averaging, computer-controlled data selection, and rigorous least-squares analysis of standard addition data for up to five simultaneous electrode inputs. (Author)

Ground fault circuit interrupter and electronic module therefor

Abstract: An electronic module for ground fault circuit interrupters (GFCI) in both circuit breaker and receptacle configurations includes a signal processor having a plurality of fault signal threshold stages for differentially charging an integrating capacitor in accordance with the magnitude of the fault signal as amplified by a high gain differential amplifier. The accumulated charge on the integrating capacitor controls the generation of a trip signal. The processor also includes a highly stable grounded neutral excitation oscillator and a noise rejection network to combat nuisance tripping.

Transient noise filter employing crosscorrelation to detect noise and autocorrelation to replace the noisey segment

Abstract: A method and circuit for detecting transient noise pulses having predetermined characteristics which are contained in an input signal, and substituting for the portion of the input signal distorted by the noise pulse, an estimate of that portion based upon portions of the input signal outside the distorted portion.

Method and apparatus for detecting cardiac arrhythmias

Abstract: A ventricular arrhythmia (or abnormal ventricular complex) monitoring technique for automatically generating an output in response to elevated low frequency content in the QRS portion of an incoming ECG wave, which is indicative of cardiac abnormalities, is improved by the addition of artifact noise detectors that temporarily interrupt the output in response to higher frequency muscle tremor and electrical interferences and to broad band, high amplitude noise and sudden baseline variations in the signal. The amplitude of the incoming ECG wave is normalized through an automatic gain control (AGC) input amplifier that receives variable gain control signals generated in accordance with the amplitude of prior QRS complexes. The variable gain control signals provide selectively variable threshold reference levels that are compared against output levels from the various detectors so that their sensitivity is automatically adjusted to match the available signal level.

Analog signal channel equalization with signal-in-noise embodiment

Abstract: Apparatus for reducing (a) background noise in a signal channel, and (b) channel gain variations, useful with spectral analysis equipment. Two feed forward circuits are disclosed: one to enhance a signal in noise (deriving an estimated signal); the other for AGC (relative to a preselected level). Background noise is estimated as a bias level corresponding to a minimum signal level detected within a preselected interval, the duration of such interval corresponding to a spectral interval of interest. Such noise estimate is then subtracted from the noisy signal of interest to provide a compensatorily biased signal or estimated signal. The compensatorily biased or estimated signal is then subjected to compensatory gain control by employing the ratio of a reference level to a peak detected level occurring within the preselected time interval as a gain control signal.

Signal identification system

Abstract: The embodiments of the signal identification system which are disclosed distinguish between signal conditions on a communication line, as for example, between noise and modulated data signals and between noise, modulated data, voice, and a no signal condition, and identify the particular type of signal condition present. In a particular system embodiment disclosed, the energy in the input signal is also examined to avoid the possibility of channelized FSK data being incorrectly classified as noise by the main system. A commutating filter is stepped across the FDM band and the energy at each step is compared with the energy at the next preceding step. The difference in energy level derived at each step is accumulated and compared with a preset level. If the accumulated energy level exceeds the preset level during the sweep, the result can be used to supersede an erroneous noise identification with a correct identification of modulated data.

Dual channel infrared intrusion alarm system

Abstract: An infrared intrusion alarm system utilizes two sensing elements and two signal processing channels arranged such that an intruder produces signals of opposite polarities in the two channels. An alarm signal is delivered only in the event that the two signals of opposite polarities are present simultaneously. Disturbances, such as component noise, which affect only one channel cannot give rise to an alarm, nor can power supply disturbances which produce signals of the same polarity in both channels.

Remote control system

Abstract: A remote control system for use in remote controlling a television receiver is provided in which a light signal is used as the remote control signal. An electroluminescent diode is used to emit the remote control light signal which is amplitude-modulated by a modulating frequency in the ultrasonic frequency range and has a very narrow band of wave lengths. The remote control system is very compact in size and completely free from the erratic operations caused by the noise.

Transfer function matrix identification

Abstract: A method is presented for identifying the transfer function matrix of a multi-input multi-output finite-dimensional continuous linear time invariant system from input-output observations in the presence of arbitrary initial conditions. A simple and efficient scheme is provided to handle these unknown initial conditions. The method avoids signal differentiation through the use of multiple integration. A set of equations, linear in the unknown parameters of the system transfer function matrix, are formed using the integrated values of inputs and outputs for different values of time. These equations are modified so as to yield an efficient method for computing the system parameters in the presence of additive measurement noise.

Flying spot scanner unaffected by ambient light

Abstract: A flying spot scanner is disclosed for scanning an object document or scene with a spot of light, and producing an electrical video signal representing the object. The scanner can be operated under normal ambient light conditions without a light-shielding enclosure. A light beam is deflected in repetitive scanning fashion over the object. The light beam is modulated in amplitude (intensity) at a radio frequency f c such as 1.2 MHz. A photodetector is positioned to receive light from the object, and it produces an unwanted electrical ambient light noise signal having a maximum frequency f a , and an electrical information signal consisting of a carrier at frequency f c modulated by a video signal having a maximum frequency f m , where f c - f m is larger than f a . The information signal is separated from the ambient light noise signal by a filter, and the information signal is demodulated to produce a facsimile or video information signal free of noise due to ambient light.

System for synchronizing local pseudo-noise sequence to a received baseband signal

Abstract: The present system generates a local PN (Pseudo Noise) sequence demodulation bit stream in synchronism with the modulation sequence of a received baseband signal The system is comprised of a PN sequence generator for generating a local PN sequence signal in response to the pulse rate of a clock signal A digital delay line generates early and late phases of the local PN sequence, which phases are correlated with the modulation sequence of the received signal Early correlation causes pulses to be inserted into the train of clock pulses while late correlation causes pulses to be deleted from the train of clock pulses A phase error less than a predetermined range (dead band) results in no adjustments to the train of clock pulses

Robust detection to stochastic signals (Corresp.)

Abstract: In this correspondence we evaluate both the large and small sample performance of a limiter-quadratic detector (LQD) for the detection of a Gaussian signal in non-Gaussian noise. The LQD is shown to be robust for small as well as large sample sizes.

An autodyne frequency tracker for laser Doppler anemometry

Abstract: A frequency tracker has been developed that produces a running average omega av of the frequency omega s of the laser doppler signal which is weighed according to the relation omega av=a2 omega s/a2, where a is the signal amplitude. It is shown that this mode of processing most effectively averages noise and ambiguity fluctuations. A practical system is described which operates at a Doppler frequency of up to 10 MHz. Measurements support predictions of response time (2 mu s at 1 MHz), accuracy and response to noise and ambiguity fluctuations. Measured long term accuracy is 0.2%.

Biological feedback systems

Abstract: A biological feedback system which is particularly useful for the processing of EEG (electroencephalogram) signals In such use the present system receives a signal from a subject organism and generates an electrical signal in response thereto Provision is made for detecting the dominant periodicity of this electrical signal, preferably as the time average of zero crossings of the signal about its own average value A first analog signal is developed having a DC magnitude which is proportional to the frequency of the periodicity A hybrid filter is used to develop the first signal by analog to digital conversion, counting and averaging the zero crossings and reconverting the average count in analog form A second analog signal is developed, the DC magnitude of which is proportional to the strength of the signal received from the subject These first and second analog signals are used to control the output of various indicators having signals which are perceptible to the subject to thereby complete a feedback loop In a preferred form of the invention these analog signals are used to control the output of a noise source so as to vary the spectral content of the noise source between high and low values in response to a change of the frequency of the signal from the subject The range of emissions from the noise source is selected to be audible to the subject when converted to sound waves The strength of the noise emission is controlled by the strength of the second analog signal and is accordingly proportional to the strength of the signal received

Solid state relay circuit

Abstract: A solid state circuit providing the function of a ratchet relay which circuit is relatively immune from noise and is capable of high speed switching operation. The circuit is adapted to receive an AC input trigger signal and convert such signal into an appropriate signal for alternately firing a pair of triacs that are each serially connected with a load and an AC power source. The circuit includes an input section comprising an AC to DC pulse converter, a time delay network, and a pulse shaping circuit which provide a clean input pulse to trigger a flip-flop and an output section including an opto-isolated Darlington transistor pair which is provided with a separate power supply and which operates to alternately fire the triacs in response to the output state of the flip-flop.

Diversity system for noise-masking

Abstract: Masking-noise speakers are positioned in an array of lines and rows to direct masking noise into a space. Two separate noise generators provide noise signals respectively to two equalizer-amplifiers which provide their signals respectively to first and second narrow band equalizers. These channel signals are respectively delivered through power amplifiers to first and second sets of speakers in the speaker array. The first and second channel signals are combined to produce a third channel signal, are power amplified, and delivered to a third set of speakers in the array so that no two adjacent speakers on any line or row are powered by the same noise signal. In a modified arrangement, the combination of the first and second channel signals is made after power amplification.