Showing papers on "Noise (signal processing) published in 1968"

Detection, Estimation, and Modulation Theory. Part 1 - Detection, Estimation, and Linear Modulation Theory.

Abstract: Detection, estimation and linear modulation theory, Part 1, covering random processes, signal detection in noise and continuous waveforms

New methods of pitch extraction

Abstract: Three new methods will be described for the extraction of the fundamental pitch from a speech signal. These are: 1) spectrum flattening followed by a minimum phase correction to synchronize harmonics 2) spectrum flattening followed by auto-correlation, and 3) nonlinear distortion followed by autocorrelation. The last two methods will be shown to be exceptionally rugged, in that they can tolerate a considerable amount of high-pass filtering and additive noise with little degradation in performance.

Reference Signal for Signal Quality Studies

Abstract: A family of reference signals for signal quality studies is described that is perceptually similar to speech signals undergoing certain signal‐dependent distortions, such as quantizing and predictive coding. This perceptual similarity can yield greater accuracy and reproducibility in subjective comparison tests than do reference signals employing additive, signal‐independent noises. Equally important, for nonstationary and the intermittent signals (such as speech) the signal‐to‐noise (S/N) ratios of the reference signals described here are defined on an instantaneous (sample‐by‐sample) basis, thus avoiding the troublesome ambiguities in measuring signal and noise powers. The distorted signal whose quality is to be evaluated can be assigned an equivalent S/N ratio independent of the time intervals over which average are extended.

Sensor-array data processing for multiple-signal sources

Abstract: Techniques are considered for processing the outputs of a sensor array that is observing J distinct signal sources Three types of wideband signals are discussed: unknown, stochastic, and parameterized Narrowband signals are a special case Four types of random errors are discussed: additive sensor noise, sensor gain errors, sensor time-delay errors, and "beam-pointing' errors It is concluded that the so-called decoupled-beam data processor is a very promising technique, which can be implemented by passing the output of J individual "beams" through a J -input, J -output linear system When sensor gain-delay and beam-pointing errors are not present, the decoupled-beam data processor provides "infinite sidelobe rejection"

Broad-Band Microwave Transmission Characteristics from a Single Measurement of the Transient Response

Abstract: A technique is presented for the measurement of the transmission and reflection scattering coefficients of microwave networks by Fourier analysis of the sampled transient response of the network to impulsive or steplike waveforms. It is demonstrated that the method can reduce errors due to mismatch of the components of the measurment system by sampling the response over a finite time domain window that excludes unwanted reflected components. A review is made of the errors introduced due to aliasing, truncation, and noiselike sources such as timing jitter and additive noise, and a description is then given of an experimental system to evaluate the technique, based on use of a 12-GHz sampling oscilloscope for measurement of the transient response and a suitable form of the fast Fourier transform algorithm. Measurements on some typical wide-band components are presented, and it is concluded that for very broad-band measurements with moderate resolution the method has a potential accuracy of about ±0.1 dB and ±1°, with a significant reduction in mismatch errors.

Optimum Signal-Processing for Pulse-Amplitude Spectrometry in the Presence of High-Rate Effects and Noise

Abstract: In this paper the idea of a general signal processing system which should satisfy various pulse rate and noise requirements is explored. Optimum processing functions (weighting functions) are considered for an ideal system, and for real conditions where effects like imperfect pole-zero cancellation are present. Time-variant filters of the gain-varying class are used to realize the required optimum weighting functions of finite width. It is shown how nonfinite-width weighting functions of some time-invariant filters can be modified into finite-width functions by switching. These switched-gain time-variant filters are somewhat limited in choice of weighting functions. A general processing system can be realized employing filters with continuously time-variant elements. In particular, a gain-varying element (i.e., an analog multiplier) can be used in conjunction with an integrator to realize arbitrary weighting functions, and therefore the theoretically maximum signal-to-noise ratio. The system is time-variant only for the noise and not for the signal, so that it does not require high precision of the time-variant element. The system output is independent of the gating interval, and does not require precise timing. A method for evaluation of such systems in terms of noise, ballistic deficit and sensitivity to parameter variations is given.

Evaluation of likelihood functions

Abstract: An expression is obtained for the likelihood function for the detection of a stochastic signal (diffusion process) in white noise. A stochastic differential equation is then obtained for the evolution of the likelihood function and the coefficients of this differential equation are related to a corresponding nonlinear filtering problem. Some extensions are noted to diffusion process signals in correlated noise and to more general stochastic signals.

Optimum multichannel velocity filters

Abstract: Optimum systems have been developed to correspond to the sub‐optimum moveout discrimination systems presented previously by several authors. The seismic data on the lth trace is assumed to be additive signal S with moveout τl, coherent noise N with moveout τ˜l, and incoherent noise Ul, expressed Il(t)=S(t-τl)+N(t-τ˜l)+Ul(t) where S, N, and Ul are independent, second order stationary random processes and τl and τ˜l are random variables with prescribed probability density functions. The signal estimate S⁁ is produced by filtering each trace with its corresponding filter Gl and summing the outputs S⁁(t)=ΣlGl(t)*Il(t). We choose the system of filters {Gl} to make the signal estimate optimum in the Wiener sense (minimum mean‐square error of the signal ensemble). For the special cases discussed, the moveouts are linear functions of the trace number l determined by the moveout/trace τ for signal and τ˜ for noise. Thus, the optimum system is determined by the probability densities of τ and τ˜ together with the no...

Characteristics of optimum multichannel stacking filters

Abstract: A large class of seismic processing operations involve the linear combination of several traces in such a way that certain “signal” events are emphasized over other “noise” events. If the noise events are randomly distributed between traces, then simple addition of the traces represents the best possible technique for suppressing the noise. However, in many cases a noise event on one trace will also occur at relatively well‐determined points on other nearby traces. For these cases, multichannel linear filters offer better discrimination against organized noise than the straight addition of traces does. Such multichannel filters can be designed with only a knowledge of the relative times of the arrivals for the various signal and noise events but with no knowledge of the actual event shapes. In addition, the filter may be specified to allow for such contingencies as the presence of random noise, variable gain between traces, and random variations of the relative time of arrival between traces. Once these p...

Improved Signal Processing Techniques for Color Television Broadcasting

Abstract: A new technique for image enhancement permits both vertical and horizontal equalization of an encoded NTSC signal without the generation of black-and-white overshoots and without the use of clippers in the main signal path. A phantom channel is used to improve the long-term drift characteristics of the equalizer. Level dependent equalization and crispening are also employed to permit a maximum of equalization with a minimum introduction of noise. A companion masking amplifier employs low-pass filters in the masking channel to permit optimum live camera, pre-gamma masking without the introduction of noise. When used together these two units produce considerable subjective improvement in the broadcast color signal.

On the Detection of a Known Signal in a Non‐Gaussian Noise Process

Abstract: In this paper, three receiver designs for the detection of a known signal in an additive non‐Gaussian noise process are considered. The noise process consists of white Gaussian noise modulated by a random‐spectrum level. The first receiver considered is an optimum (likelihood) processor and the remaining two receivers are suboptimum designs consisting of a cross correlator and a likelihood correlator. The basic processing operations of the three receivers are investigated and compared on the basis of their effects in observation space. The performance of each receiver is evaluated and presented in terms of ROC curves. A comparison of the performance curves indicates a loss in optimum performance as compared to the Gaussian noise case and a significant loss in performance of the suboptimum receivers relative to the optimum receiver.

Method and apparatus for the suppression of noise in process control systems

Abstract: A method of noise suppression and the apparatus therefor is provided wherein the distinctive rate of change of the noise signal is relied upon to achieve the isolation and suppression thereof. In one embodiment of the disclosed invention, the composite waveform including the noise and information component signals is applied to both a linear and a nonlinear signal transfer means. The nonlinear transfer means is designed so that it will only pass the entire magnitude of signal components having a relatively high rate of change and thus only the noise component is wholly passed thereby. Thereafter, the isolated noise component signal is subtracted from the composite waveform as passed by the linear transfer means and a substantially noisefree information signal is thereby obtained.

On the Selection of Signals for Phase-Locked Loops

Abstract: The performance of phase-locked loops and related signal tracking devices is dependent upon the cross-correlation function between the input signal and a locally generated signal. This paper is concerned with the problem of selecting both the input and local signals so as to minimize the tracking error due to additive noise.

Gas laser pressure control for maintaining constant pressure

Abstract: A SENSOR CIRCUIT IS PROVIDED FOR DETECTING A REDUCTION IN THE GAS PRESSURE OF AN ION LASER. THE NOISE SIGNAL VOLTAGES IN THE PLASMA CURRENT OF THE GAS LASER INCREASE RAPIDLY WITH A REDUCTION IN PRESSURE. THE SENSOR TAKES ADVANTAGE OF THIS PHENOMENON BY DETECTING THE NOISE SIGNAL SPECTRUM IN THE PLASMA CURRENT. A DISCRIMINATING CIRCUIT PASSES ONLY THOSE NOISE SIGNALS IN THE NOISE SPECTRUM EXCEEDING A PREDETERMINED VOLTAGE VALUE AND PROVIDES A CONTROL SIGNAL WHENEVER THE GAS PRESSURE FALLS BELOW A PREDETERMINED VALUE RESULTING IN THE INCREASED VOLTAGE NOISE SIGNALS. THIS CONTROL SIGNAL IS UTILIZED TO OPERATE A SOLENOID VALVE TO AUTOMATICALLY PASS REFILL GAS TO THE LASER TUBE AND THEREBY MAINTAIN THE GASS PRESSURE IN THE TUBE WITHIN A PREDETERMINED PRESSURE RANGE.

Secret-signalling system utilizing noise communication

Abstract: A secret-signaling, transmitted-reference, spread-spectrum system, utiliz a suppressed-noise carrier for the information signal in combination with a delayed-noise, suppressed carrier of a fixed frequency in order to spectrum-spread the voice signal across the noise signal in the same frequency band. The receiver of the system delays the transmitted signal input which is taken together with the undelayed transmitted signal to determine correlation in order to extract, from the transmitted spread-spectrum signal, solely the information signal generated.

Apparatus for measuring the difference in phase between two signals of the same frequency, one having noise associated therewith

Abstract: APPARATUS FOR MEASURING THE DIFFERENCE IN PHASE, FROM 0* TO 180*, BETWEEN A NOISE-FREE SIMUSOIDAL REFERENCE SIGNAL OF A PREDETERMINED FREQUENCY AND AN UNKNOWN SINUSOIDAL SIGNAL OF THE SAME FREQUENCY BUT HAVING NOISE ASSOCIATED THEREWITH. THE UNKNOWN AND REFERENCE SIGNALS ARE APPLIED TO RESPECTIVE LIMITERS AND CONVERTED TO SQUAREWAVE PULSE TRAINS WHICH TRIGGER, RESPECTIVELY, A SAMPLEPULSE GENERATOR AND A RAMP GENERATOR. SAMPLING PULSES ARE PRODUCED BY THE PULSE GENERATOR AND USED TO SAMPLE A TRAIN OF RAMP VOLTAGE SIGNALS APPLIED TO A SAMPLE-ANDHOLD CIRCUIT BY THE RAMP GENERATOR. THE SAMPLED SIGNAL PORTIONS ARE CONVERTED IN THE SAMPLE-AND-HOLD CIRCUIT TO A CONTINUOUS VOLTAGE SIGNAL OF VARYING AMPLITUDE REPRESENTATIVE OF THE PHASE DISPLACEMENT BETWEEN THE UNKNOWN AND REFERENCE SIGNALS. THE NOISE CONTENT OF THE CONTINUOUS VOLTAGE SIGNAL IS REDUCED BY A LOW-PASS FILTER TO PROVIDE AN ANALOG SIGNAL REPRESENTATIVE OF THE PHASE DISPLACEMENT BETWEEN THE REFERENCE AND UNKNOWN SIGNALS. TO PROVIDE A DIGITAL REPRESENTATION, THE ANALOG SIGNAL IS APPLIED TO AN ANALOG COMPARATOR TOGETHER WITH THE TRAIN OF RAMP VOLTAGE SIGNALS. THE COMPARATOR COMPARES THE SIGNALS AND PRODUCES A SQUARE-WAVE PULSE TRAIN REPRESENTING THE PHASE DISPLACEMENT BETWEEN THE UNKNOWN SIGNAL AND THE REFERENCE SIGNAL, WHICH PULSE TRAIN IS USED TO GATE CLOCK SIGNALS T A DIGITAL COUNTER WHICH PROVIDES A DIGITAL INDICATION OF THE AMOUNT OF PHASE DISPLACEMENT.

Signal design for a class of clutter channels.

Abstract: Optimal signal selection for transmission over channel with clutter noise component increase as function of signal energy

Multichannel deconvolution filtering of field recorded seismic data

Abstract: Several writers have proposed the use of multichannel filters for the elimination of coherent noise on seismic records One filter of this type which can be constructed is a multichannel Wiener filter which has a multichannel input and a single channel output In this form, it is applicable to data collected for vertical or horizontal common‐depth‐point stack processing The choice of desired output characteristics for this Wiener filter is flexible and, for example, can be tuned to correspond to multichannel deconvolution The results of the application of filters of this type to field and synthetic data, in general, show little if any advantage over single‐channel deconvolution This failure appears to be connected with the low cross coherence of both noise and reflection signal on field‐recorded, common‐depth‐point traces

Receiver-operating characteristics determined under several interaural conditions of listening.

Abstract: The ability of subjects to detect sinusoidal signals in a continuous background of white Gaussian noise was investigated for several different interaural relations of the signal and of the noise stimuli. The functions, referred to as receiver operating characteristics (ROC's), relating the proportion of correct detections of the signal to the proportion of false alarms were determined in each case. A rating procedure was employed to determine the ROC's. The area under the ROC was found to be a good estimate of the percent correct obtained with a two‐interval forced‐choice (2IFC) technique—a relation to be expected on theoretical grounds. The ROC's were not significantly affected by the presence of trial‐by‐trial feedback.

Stereo multiplex decoding system with a phase locked loop switching signal control

Abstract: A stereo decoding system for FM receivers that is compatible with integrated circuit techniques and contains a phase locked loop to provide stability for the demodulator switching signal. Carrier noise is maintained at a minimum by a narrow equivalent band pass filter and in particular embodiments no inductors are required.

The linear random process

Abstract: A survey of the theory and applications of the class of random processes is presented. Topics discussed include the law of large numbers, covariance estimation, and the relationship of linear to normal processes. Various applications of the linear process to problems of communication theory are considered. These include prediction, signal extraction, and detection, using the linear process as a model for the signal or noise. Several exmples illustrating certain aspects of linear processes are given.

Measurement of Pilot Describing Functions from Flight Test Data with an Example from Gemini X

Abstract: It is well known that there is an error in identifying the pilot describing function from routine flight test records because the pilot's output noise is correlated with the input error signal. This paper shows that this identification error can be reduced in the computer processing by shifting the input signal an amount equivalent to the pilot's time delay. This technique for reducing the identification error is analyzed with theory and is demonstrated with the identification of a simulated pilot model. This technique is also applied to flight test records obtained from the retrofire phase of the Gemini X mission.

Optimum, non-linear processing of noisy images

Abstract: It has been traditional to constrain image processing to linear operations upon the image. This is a realistic limitation of analog processing. In this paper, we find the optimum restoration of a noisy image by the criterion that expectation 〈 ∣Oj-O¯j∣K〉 be a minimum. Subscript j denotes the spatial frequency ωj at which the unknown object spectrum O¯ is to be restored, O¯ denotes the optimum restoration by this criterion, and K is any positive number at the user’s discretion. In general, such processing is nonlinear and requires the use of an electronic computer. Processor O¯ uses the presence of known, Markov-image statistics to enhance the restoration quality and permits the image-forming phenomenon to obey an arbitrary law Ij = ℒ(τj, Oj, Nj). Here, τj denotes the intrinsic system characteristic (usually the optical transfer function), and Nj represents a noise function. When restored values O¯ j, j=1, 2, ⋯, are used as inputs to the band-unlimited restoration procedure (derived in a previous paper), the latter is optimized for the presence of noise. The optimum O¯ j is found to be the root of a finite polynomial. When the particular value K=2 is used, the root O¯ j is known analytically. Particular restorations O¯ j are found for the case of additive, independent, gaussian detection noise and a white object region. These restorations are graphically compared with that due to conventional, linear processing.

Effect of Signal Duration on Detection for Gated and for Continuous Noise

Abstract: A series of two‐alternative forced‐choice experiments showed that for short durations, the detection of a tonal signal in noise when the two are gated synchronously is superior to the detection of the signal in a background of continuous noise. The experiments also showed that for gated signal and noise, there is a steady improvement in detection as the duration is shortened, provided that highly practiced observers are employed in the task. Naive observers exhibit a similar trend, but their performance drops at the short durations (5 and 10 msec) where the listening task becomes very difficult.

Pitch synchronous reduction of signal envelope

Abstract: BY REDUCING THE ENVELOPE OF A SIGNAL, SUCH AS A SPEECH SIGNAL, IN A NONLINEAR FASHION A MODIFIED SIGNAL IS PRODUCED WHICH, IN ADDITION TO BEING HIGHLY INTELLIGIBLE, EXHIBITS DESIRABLE PROPERTIES. PITCH SYNCHRONOUS GAPS, SMOOTHLY ESTABLISHED IN A REDUCED ENVELOPE SIGNAL IN PLACE OF INTERVALS OF LOW SIGNAL LEVELS, ARE EFFECTIVE IN ELIMINATING NOISE WHICH MASKS LOW LEVEL SIGNALS, REDUCING REVERBERATION, AND IN ADAPTING THE SIGNAL FOR MULTIPLEX TRANSMISSION. ENVELOPE REDUCTION IS EFFICIENTLY ACHIEVED BY CONTROLLABLY CENTER CLIPPING A SELECTED MOFULATION SIDEBAND OF A SIGNAL, FILTERING THE RESULTANT, AND RESTORING THE SIGNAL TO BASEBAND.

Yarn speed measurement on the basis of yarn noise

Abstract: A yarn testing device having means for measuring the yarn speed. The device includes a pickup member for deriving a yarn signal from the passing yarn. The yarn signal includes a noise signal component produced by normal irregularities of the yarn, the amplitude and frequency thereof being proportional to yarn speed. A high pass network passes only the noise signal to an amplitude or frequency detector in which it is compared with a reference voltage indicative of a reference yarn speed to derive a signal proportional to yarn speed.

Some electronic problems of myoelectric control of powered orthotic and prosthetic appliances.

Abstract: In this paper the literature on the myoelectric signal is collected and reviewed for purposes of determining the electronic characteristics from which the optimum specifications for an amplifier used in a myoelectric control system are determined. An average figure of 5,000 ohms at 10 cycles per second is given as the output impedance of tissue. Accepting a 1 per cent signal loss, the input impedance of the amplifier should be at least 500,000 ohms. By integrating curves from the literature, it is fourid that the signal energy band is from 25 to 300 cycles per second as determined by the maximum signal/noise ratio in conjuction with a 1 per cent signal loss. The pass band of the amplifier should then be 25 to 300 cycles per second. Various other electronic problems of myoelectric control are discussed such as type of amplifier, electrodes, alternating current noise pickup, signal variation, and tissue noise.

An optimum decision-directed scheme for Gaussian mixtures

Abstract: The problem of making measurements upon some available signal mixture in order to extract or estimate certain parametric data for subsequent signal detection using the measurement data is considered. The development is carried out for a formal binary signal observation mixture (no a priori classification of the observations into isolated category or class ensembles is assumed), with the parameters of the noise and pulse waveforms unknown. Two categories of multidimensional mixture-resolving estimators are treated: an optimized decision-directed category and a moment method category. In the former, the optimization is formulated to minimize a measure of distance and dispersion with a constraint adjustment to "maximize" a measure of convergence rate. An eigenvalue theory approach is applied to illustrate the relationship of the measurement data to the detector structure. An experimental case study is carried out via digital computer simulation, and a comparison of error probability performance characteristics with the conventional decision-directed and Bayes matched-filter techniques is made. Results of the simulation are presented which indicate quantitatively the superiority of the estimators over conventional decision-directed techniques, in terms of convergence rates and asymptotic performance characteristics.