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Showing papers on "Noise (signal processing) published in 1976"


Journal ArticleDOI
TL;DR: It is concluded that limits of attention in dual-task performance are more severe in output than in input stages of processing, but that these limits are not necessarily those of a single-channel bottleneck.
Abstract: Six subjects performed a manual tracking task concurrently uith each of two secondary tasks: in input task (auditory signal detection) and an output task (application of a constant force). A feedback-control analysis of tracking performance was utilized to analyze the time-sharing decrements observed in mean squared errer, in terms of components due to processing delay, addition of internal processing noise, and change in response bias (tracking gain). The results indicated that only the parameters measuring noise and gain were sensitive to time-sharing conditions, and these only to concurrent performance of the force application task. It is concluded that limits of attention in dual-task performance are more severe in output than in input stages of processing, but that these limits are not necessarily those of a single-channel bottleneck. Instead, a broader conception of attention is proposed: one that included changes in processing noise and shifts in response bias, as attention-related phenomena.

130 citations


Journal ArticleDOI
TL;DR: In this paper, a non-linear N-th root method of processing seismic array data is investigated for both event detection and event processing for both seismic array and event classification, and it has been found that this process is much better at handling non Gaussian noise and is only very marginally worse than linear processing when the noise is Gaussian.
Abstract: Summary A non-linear N-th Root method of processing seismic array data is investigated for both event detection and event processing For event detection it has been found that this process is much better at handling non Gaussian noise and is only very marginally worse than linear processing when the noise is Gaussian For event processing its chief advantage is the suppression of sections of the record where the signal-to-noise ratio is low, enabling more precise azimuth and slowness measurements to be made

92 citations


Journal ArticleDOI
K. Mueller1
TL;DR: A new approach to echo canceling for two-wire fullduplex data transmission is proposed, using a transversal filter approach, and the usual multiplications are replaced by additions and subtractions thus allowing efficient operation of a large number of taps as required for the canceling of distant echoes.
Abstract: A new approach to echo canceling for two-wire fullduplex data transmission is proposed. The canceling signal is directly synthesized from the binary data, using a transversal filter approach, and the usual multiplications are replaced by additions and subtractions, thus allowing efficient operation of a large number of taps as required for the canceling of distant echoes. As a specific application, a system processing one sample per baud is discussed where timing signals at both communicating stations are assumed to be synchronized. A stochastic adjustment gradient-type algorithm is used for both training and adaptive tracking of the canceler. It is shown that convergence does not depend on intersymbol interference, timing phase, carrier phase, or the energy ratio of the local to the received signal, but is a function only of the number of taps. Convergence time is proportional to that number, and the optimum step size for fastest convergence is equal to the reciprocal of the number of taps. The residual fluctuation noise is proportional to that part of the mean-square (MS) error which cannot be reduced by the canceler and is a simple function of the product of the tap signal and the step size. The predicted convergence properties are verified by simulation results. Finally, it is shown how such an echo canceler might be used to allow two-wire full-duplex transmission for data rates as high as 4800 bit/s.

90 citations


Proceedings Article
01 Mar 1976
TL;DR: In this paper, the use of EMG as a proportional control signal for prostheses is reviewed, and the lack of success of existing proportional EMG-controlled prostheses was attributed in the greater part to the presence of low frequency "noise" in the processed EMG signal.
Abstract: The use of EMG as a proportional control signal for prostheses is reviewed. The lack of success of existing proportional EMG-controlled prostheses is shown to be attributable in the greater part to the presence of low frequency "noise" in the processed EMG signal. If EMG is to yield useful proportional information, this noise must be eliminated, and to this end the methods of processing EMG are reviewed and the sources of noise examined. A number of methods for its removal are discussed.

85 citations


Patent
21 Dec 1976
TL;DR: In this paper, an orthogonal transform of the input signal is derived, which has n transformed signal components and at least some of these signal components are suppressed if their respective signal levels are less than a threshold level.
Abstract: A method of and apparatus for reducing the noise of an input signal, such as a composite video signal. An orthogonal transform of the input signal is derived, this orthogonal transform having n transformed signal components. At least some of these signal components are suppressed if their respective signal levels are less than a threshold level. Preferably, the n transformed signal components correspond to different portions of the input signal; and those components representing the higher frequency portions are suppressed if their signal levels are less than the threshold level. Following this signal suppression, the n transformed signal components are reconverted into substantially the input signal, less the suppressed components.

84 citations


Patent
24 Sep 1976
TL;DR: In this article, the authors proposed a frequency shift keying data transmission system for transmission of binary coded information in which the mark of the coded pulse waveform was represented by a half cycle of one keying frequency and the space is represented by another keying frequencies.
Abstract: It is important that a data transmission system should be fast, utilize a minimum of band width and be accurate in the presence of high noise levels. The invention provides a frequency shift keying data transmission system for transmission of binary coded information in which the mark of the coded pulse waveform is represented by a half cycle of one keying frequency and the space is represented by a half cycle of another keying frequency. An improvement in speed, band width utilization and accuracy at high noise levels is obtained by providing that the transmission signal is an approximately sinusoidal waveform of which the phase is continuous at the transitions, the time lengths of the mark and space symbols thereof are matched to the half time periods of the respective keying frequencies and the slope is constant at the cross-over points.

81 citations


Proceedings Article
01 Jan 1976
TL;DR: In this paper, the problem of estimating a discrete-time stochastic signal which is corrupted by additive white measurement noise is discussed, and the stationary solution to the fixed-lag smoothing problem can be obtained.
Abstract: The problem of estimating a discrete-time stochastic signal which is corrupted by additive white measurement noise is discussed How the stationary solution to the fixed-lag smoothing problem can be obtained is shown The first step is to construct an innovation model for the process It is then shown how the fixed-lag smoother can be determined from the polynomials in the transfer function of the innovation model In many applications, the signal model and the characteristics of the noise process are unknown It is shown that it is possible to derive an algorithm which on-line finds the optimal fixed-lag smoother, a self-tuning smoother The self-tuning smoother consists of two parts: an on-line estimation of the parameters in the one-step ahead predictor of the measured signal, and a computation of the smoother coefficients by simple manipulation of the predictor parameters The smoother has good transient, as well as good asymptotic, properties (Less)

78 citations


Patent
10 Nov 1976
TL;DR: In this article, a system for reducing noise in a color video signal which utilizes frame store integration and includes a delay or storage device for storing a single television frame, a summing device for adding a fractional amplitude portion of the signal stored in the storage device to a fraction of the present video signal, and a chrominance corrector circuit for altering the chrominance component of the stored signal so as to be in the proper phase relationship to be summed with the present signal.
Abstract: A system for reducing noise in a color video signal which utilizes frame store integration and includes a delay or storage device for storing a single television frame, a summing device for adding a fractional amplitude portion of the signal stored in the storage device to a fractional amplitude portion of the present video signal, and a chrominance corrector circuit for altering the chrominance component of the stored signal so as to be in the proper phase relationship to be summed with the chrominance component of the present video signal. The system is operative automatically to change the fractional amplitude portion of the stored signal fed back to the summing device as a function of the difference between stored and present signals thereby to change the integration time constant of the system to accommodate for motion between the present signal and the stored frames. The system functions as a comb filter whose tines are very narrow when there is little or no motion between the present and stored frames and which are automatically widened to allow motion to be portrayed when there is relative motion between past and present signals.

77 citations


PatentDOI
TL;DR: In this paper, the transposed formant frequencies are determined at successive intervals in the speech signal using a fixed value, greater than 1, and added to this fixed value is another fixed value to obtain what are called transposed fundamental frequencies.
Abstract: A hearing aid system and method includes apparatus for receiving a spoken speech signal, apparatus coupled to the receiving apparatus for determining at successive intervals in the speech signal the frequency and amplitude of the largest formants, apparatus for determining at successive intervals the fundamental frequency of the speech signal, and apparatus for determining at successive intervals whether or not the speed signal is voiced or unvoiced. Each successively determined formant frequency is divided by a fixed value, greater than 1, and added thereto is another fixed value, to obtain what are called transposed formant frequencies. The fundamental frequency is also divided by a fixed value, greater than 1, to obtain a transposed fundamental frequency. At the successive intervals, sine waves having frequencies corresponding to the transposed formant frequencies and the transposed fundamental frequency are generated, and these sine waves are combined to obtain an output signal which is applied to a transducer for producing an auditory signal. The amplitudes of the sine waves are functions of the amplitudes of corresponding formants. If it is determined that the speech signal is unvoiced, then no sine wave corresponding to the transposed fundamental frequency is produced and the other sine waves are noise modulated. The auditory signal produced by the transducer in effect constitutes a coded signal occupying a frequency range lower than the frequency range of normal speech and yet which is in the residual-hearing range of many hearing-impaired persons.

74 citations



Proceedings ArticleDOI
12 Apr 1976
TL;DR: A maximum likelihood (ML) estimator is derived for determining time delay between two signals observed in the presence of uncorrelated noise, under the assumptions of known signal and noise spectral characteristics.
Abstract: A maximum likelihood (ML) estimator is derived for determining time delay between two signals observed in the presence of uncorrelated noise, under the assumptions of known signal and noise spectral characteristics. This ML estimator can be realized as a pair of receiver prefilters followed by a cross correlator. The time argument at which the correlator achieves a maximum is the delay estimate. Qualitatively, the role of the prefilters is to weight the signal passed to the correlator according to the strength of the coherence function. Other realizations of the ML processor are also discussed. The variance of a generalized correlation time delay estimator is derived when the estimate is in the neighborhood of the true delay. An example using these results is given with emphasis on the effect of erroneously specifying the frequency weighting to be employed. Limitations of the derived results are also discussed.

Journal ArticleDOI
TL;DR: In this paper, a method for image deblurring in spatially incoherent illumination is described, where an additional step of illuminance subtraction is added to simulate negative intensities, and the use of computer-generated holograms of a low number of cells.
Abstract: Under coherent illumination, the interference between signal and noise produces an amplification of the noise. That is why image processing by optical methods may be done better with incoherent light than with coherent light. A method is described where image deblurring is performed in spatially incoherent illumination. The two main features are an additional step of illuminance subtraction to simulate negative intensities, and the use of computer-generated holograms of a low number of cells.

Patent
06 Aug 1976
TL;DR: In this paper, a dual channel receiver system for receiving polarized signals, which system reduces cross-interference between the signal channels by utilizing adaptive filter equalization means responsive to the input received signals and to error control signals for providing a plurality of weighting signals which are used to combine selectively with the inputs to reduce the errors, including particularly cross-polarization and noise errors therein.
Abstract: A dual channel receiver system for receiving polarized signals, which system reduces cross-interference between the signal channels by utilizing adaptive filter equalization means responsive to the input received signals and to error control signals for providing a plurality of weighting signals which are used to combine selectively with the input received signals to reduce the errors, including particularly cross-polarization and noise errors therein. The channels each include decision-directed error signal generating means for providing such error control signals. The system also includes means for preventing system failures wherein both received signals fade simultaneously under which conditions data reversal in the channels could occur and wherein one received signal fades under which condition the same data is produced in both channels.

Patent
26 Apr 1976
TL;DR: In this paper, the authors compare signals from successive frame or field scans and note the differences, where low amplitude differences are assumed to represent noise and are attenuated by a factor K. Differences above a predetermined level are not so attenuated.
Abstract: Reduction of noise in a television signal is achieved by comparing signals from successive frame or field scans and noting the differences. Low amplitude differences are assumed to represent noise and are attenuated. Differences above a predetermined level are assumed to represent movement and are not so attenuated by a factor K. Where there are inherent differences between the signals compared, for example they are different fields of an interlaced scan or are color signals with different subcarrier phases, the signal from the earlier scan is modified to compensate for these differences and provide a signal for comparison which is a better estimate of the expected signal on the later scan.

Patent
17 May 1976
TL;DR: In this article, a signal proportional to engine speed is provided and a circuit responsive to the speed signal generates a background noise reference signal which is subtracted from the electrical signal therefore producing a knock intensity signal.
Abstract: Spark knock in an internal combustion engine is detected by an accelerometer attached to the intake manifold which generates electrical signals representing inaudible background engine noise combined with knock. A signal proportional to engine speed is provided and a circuit responsive to the speed signal generates a background noise reference signal which is subtracted from the electrical signal therefore producing a knock intensity signal. That signal is in turn compared with another speed variable reference signal representing borderline knock level so that the resultant output is a signal representing the amount by which the knock intensity exceeds the borderline value. Each reference signal is generated by a diode function generator in response to the speed signal.

Patent
26 Jul 1976
TL;DR: In this article, the estimated noise signal is an rms value averaged over a large number of measurements and the most significant bits in the accumulator are decoded and converted to an analog voltage which is a measure of the signal-to-noise power ratio of the baseband signal.
Abstract: Signal monitoring apparatus in which a baseband signal including noise is compared at timed intervals with a reference signal and an estimated noise signal from an estimated noise signal generator Indications of whether the estimated noise signal is higher or lower than the noise level present in the signal are applied to a digital accumulator in the estimated noise signal generator Certain of the most significant bits in the accumulator are employed to generate the analog estimated noise signal An arrangement for preventing or permitting the passage of indications to the accumulator approximates the Rayleigh distribution of differential error probabilities about the estimated noise signal being generated The result is that the estimated noise signal is an rms value averaged over a large number of measurements Certain of the most significant bits in the accumulator are decoded and converted to an analog voltage which is a measure of the signal-to-noise power ratio of the baseband signal

Journal ArticleDOI
TL;DR: The total signal power to total noise power (S/N) alone is an insufficient measure for setting the cepstrum performance, and relative bandwidths of signal and noise are also needed.
Abstract: Often, the cepstrum has been used when estimating the time delay r between elements of a composite signal embedded in noise, n(t) . Here a probabilistic analysis is conducted dealing with the effect of stationary Gaussian noise on the characteristics of such a nonlinear processor. The input noise, n(t) is reflected at the cepstrum's output as: 1) modulation M_{1}(\omega) of sinusoidal information carrier with subsequent reduction in the height of echo peak at \tau ; and 2) generation of background noises \hat{phi}(\omega) and \hat{psi}(\omega) with tendency to obscure that echo peak. The resulting probabilities of these terms are derived. The expected mean and standard deviation of reduction in the peak level at \tau due to noise are analytically described. Similar statistical measures on the background noise are also obtained. The results point out the dependence of the-statistical measures upon the pointwise variation of input signal to noise spectra. Thus the total signal power to total noise power (S/N) alone is an insufficient measure for setting the cepstrum performance, and relative bandwidths of signal and noise are also needed. The detection probability P_{D} of a peak corresponding to \tau is calculated for exponential spectra with equal bandwidths in signal and noise and with echo strength a = 0.4; P_{D} is found to be close to one for an SIN greater than -4 dB; deterioration in detection is found to be rapid with thresholding near an S/N \sim -6 db where P_{D} falls to 0.3.

Patent
13 Sep 1976
TL;DR: In this article, a digital communications system of the type transmitting data on a plurality of modulated FDM carriers interspersed between harmonics of a systemwide signal and utilizing a main synchronized detector at a receiving end, is immunized to signal degradation due to reception of "noise" from both the shifting of signal harmonics and the modulation sidebands of adjacent carriers into the passband of the desired communications signal during at least synchronization acquisition.
Abstract: A digital communications system of the type transmitting data on a plurality of modulated FDM carriers interspersed between harmonics of a system-wide signal and utilizing a main synchronized detector at a receiving end, is immunized to signal degradation due to reception of "noise" from both the shifting of signal harmonics and the modulation sidebands of adjacent carriers into the passband of the desired communications signal during at least synchronization acquisition by methods of interference minimization including: emplacing each data carrier at a frequency mid-way between adjacent harmonics; locking the frequency of the data carrier to the system-wide signal frequency to maintain the communications frequency exactly mid-way between two adjacent harmonics of the latter signal; transmitting the data in digital form and modulating each data carrier at a baud essentially equal to an exact even submultiple of the system-wide potentially-interfering signal, and detecting the transmitted digitally-modulated carrier at the receiving end by use of long-time-constant bandpass filters. Similar integrating filters, having means for discharging the storage elements thereof after each baud time period as determined by a baud clock synchronized to the system-wide signal, are utilized for the main synchronized data detector.

Patent
30 Dec 1976
TL;DR: In this article, a dual channel signal detector circuit comprising an equalizer for responding to a variable peak amplitude input signal, in which the peaks are representative of data, was proposed to provide a substantially constant peak amplitude output signal having discrete data representative pulses spaced along a base line, which is substantially flat at the zero level in regions intermediate the pulses, for application to separate peak detection and amplitude detection channels.
Abstract: A dual channel signal detector circuit comprising an equalizer for responding to a variable peak amplitude input signal, in which the peaks are representative of data, so as to provide a substantially constant peak amplitude output signal having discrete data representative pulses spaced along a base line, which is substantially flat at the zero level in regions intermediate the pulses, for application to separate peak detection and amplitude detection channels. The peak detection channel produces data pulses each indicative of the relative time occurrence of the peak of a respective data representative pulse while the amplitude detection channel is triggered by signal levels of the data representative pulses exceeding a predetermined threshold to produce gating pulses for gating the data pulses to the circuit output substantially exclusive of any noise that may be present at the input of the circuit.

Journal ArticleDOI
TL;DR: The technique of subthreshold addition of sinusoidal gratings was used to analyse the visual system of man during the perception of edges, lines, and bars and can be described as a matched filter which extracts an input signal contaminated with noise of specified spectral energy density.
Abstract: The technique of subthreshold addition of sinusoidal gratings was used to analyse the visual system of man during the perception of edges, lines, and bars. The experimentally obtained sensitivity function varies in close relationship to the test pattern, and can be factorized into the conjugate complex spectrum of the test pattern at threshold and a pattern-invariant function of spatial frequency. Interpreting the sensitivity function as transfer function, which is possible under certain conditions, we can describe the visual system as a matched filter which extracts an input signal contaminated with noise of specified spectral energy density. Questions discussed refer to the spatial operations occurring in matched filters, the relationship between the modulation transfer function for sine-wave gratings and the pattern-invariant transfer component, the exact determination of elements within the theoretical concept, and the realization of matched filters by the nervous system.

Journal ArticleDOI
TL;DR: In this paper, a new approach is taken to the problem of tracking a fixed amplitude signal with a Brownian motion phase process, where the problem is treated via estimation of the quadrature signal components.
Abstract: A new approach is taken to the problem of tracking a fixed amplitude signal with a Brownian motion phase process. Classically, a first-order phase-lock loop (PLL) is used; here, the problem is treated via estimation of the quadrature signal components. In this space, the state dynamics are linear with white multiplicative noise. Therefore, linear, minimum-variance filters, which have a particularly simple mechanization, are suggested. The resulting error dynamics are linear at any signal/noise ( S/N ) ratio unlike the classical PLL. During synchronization, and above threshold, this filter with constant gains degrades by 3 percent in output rms phase error with respect to the classical loop. However, up to 80 percent of the maximum possible noise improvement is obtained below threshold where the classical loop is nonoptimum, as demonstrated by a Monte Carlo analysis. Filter mechanizations are presented for beth carrier and baseband operation. An interesting bandpass filter interpretation is given.

Journal ArticleDOI
TL;DR: Simulation of defined‐ and nondefined‐interval tasks with an energy detector showed that this device performs very similarly to the human listener in both cases.
Abstract: Ability to detect tones in noise was measured without defined observation intervals. Latency density functions were estimated for the first response following a signal and, separately, for the first response following randomly distributed instances of background noise. Detection performance was measured by the maximum separation between the cumulative latency density functions for signal-plus-noise and for noise alone. Values of the index of detectability, estimated by this procedure, were approximately those obtained with a 2-dB weaker signal and defined observation intervals. Simulation of defined- and non-defined-interval tasks with an energy detector showed that this device performs very similarly to the human listener in both cases.

Patent
25 May 1976
TL;DR: In this article, the system includes a current source as energized by an input wave generator providing an input signal of predetermined frequency content, amplitude relationship and duration; in addition, a plurality of energy receiving detectors are utilized in equi-spaced array such that differential electrical measurement between successive detectors may be gained during each single input energy operation.
Abstract: A method of induced polarization geophysical surveying which derives meaningful parameters relative to the subsurface strata in both time domain and frequency domain for comparison and/or deductive data compilation and graphic depiction. The system includes a current source as energized by an input wave generator providing an input signal of predetermined frequency content, amplitude relationship and duration; in addition, a plurality of energy receiving detectors are utilized in equi-spaced array such that differential electrical measurement between successive detectors may be gained during each single input energy operation. Such differential electrical measurements are further susceptible of cross correlation relative to the input current signal to provide increased signal-to noise differentiation with respect to usable induced polarization resultant values.

Patent
20 Dec 1976
TL;DR: In this paper, a combiner combines the estimated noise and original input signal to develop an output speech signal free of noise, which is then applied to a spectrum shaper to restore a natural shape.
Abstract: Noise such as hum (whose components are self-correlated over a long time-interval) is estimated (separated) from Signal such as speech (whose components are self-correlated only over a short time-interval) by using a time-domain transversal filter, whose tap-weight coefficients may be fixed (Wiener filter) or variable (Adaptive filter). A combiner combines the estimated noise and original input signal to develop an output speech signal free of noise. The output speech may by further applied to a spectrum shaper to restore a natural shape.

Journal ArticleDOI
TL;DR: Observations indicate that CI corresponds to an early stage in binaural interaction which generally escapes notice because of further perceptual processing.
Abstract: Binaural interaction was studied using headphones presenting signals (tones or filtered speech) to one ear and noises of various spectral compositions to the other. Every half-second, the sides receiving the signal and noise were reversed. The noise was always perceived to alternate from side to side, but the signal appeared to be stationary and diffusely localized about the midsaggital plane when the noise contained the spectral components of the signal at appropriate intensity levels. This delateralization of a monaural signal results from a process called “contralateral induction” (CI). Additional observations indicate that CI corresponds to an early stage in binaural interaction which generally escapes notice because of further perceptual processing.

Patent
26 Jul 1976
TL;DR: In this paper, a linear control-attenuation circuitry, and ganged input-output manual level controls for dynamic range matching at constant overall gain, were proposed for noise suppressor systems.
Abstract: A noise suppressor system uses a set of parallel bandpass filters to transform an input signal into a plurality of spectral adjacent band signals. Each band signal may then be substantially attenuated (squelched) by an attenuation-control circuit when it drops below a predetermined noise threshold. All band signals are then summed to reform essentially the original but noise-suppressed signal. Features of the invention include essentially linear control-attenuation circuitry, and ganged input-output manual level controls for dynamic range matching at constant overall gain.

Patent
07 Jun 1976
TL;DR: A signal presence detection method for use in systems where a multiplicity of types of noise is expected, wherein the spectral characteristics of the input wave is compared with corresponding characteristics of expected noise wave and wherein the determination that signal is present is made only if the input signal mismatches all of the compared noise waves' spectral characteristics.
Abstract: A signal presence detection method for use in systems where a multiplicity of types of noise is expected, wherein the spectral characteristics of the input wave is compared with corresponding characteristics of the expected noise wave and wherein the determination that signal is present is made only if the input wave mismatches all of the compared noise waves' spectral characteristics. Another embodiment of the invention compares the waveshape of the input wave and the noise waveshape. As a result of this procedure, a sensitive signal presence indication is obtained which is relatively immune to noise level.

Patent
27 Dec 1976
TL;DR: In this paper, a self-synchronous detection of amplitude variations of the envelope of the bandpass-filtered ac signal is proposed to reduce false detection of modulation information when noise or other spurious signals accompany the modulated ac signal.
Abstract: Demodulation of an ac signal that has been modulated by discrete changes in its amplitude, frequency or phase, is effected by first feeding the modulated ac signal through an amplitude limiter and hence through a bandpass filter tuned to a preselected frequency of the ac signal. The resulting bandpass-filtered ac signal defines a variable amplitude envelope which varies in response to amplitude, frequency or phase modulations of the input ac signal. Amplitude variations of the envelope of the bandpass-filtered ac signal are detected by a switching circuit whose operation has been termed "self-synchronous," because it is synchronized to the frequency of the ac signal prior to the passage of the ac signal through the bandpass filter. More particularly, the switching circuit is opened and closed in response to the ac signal appearing at the input to the bandpass filter, to cause alternate, like-polarity half cycles of the bandpass-filtered ac signal to be selectively conducted to a low-pass filter. Filtering by the low-pass filter extracts modulation information from the detected envelope thereby completing the demodulation process. By virtue of the "self-synchronous" detection, the demodulation process is less prone to false detection of modulation information when noise or other spurious signals accompany the modulated ac signal, and is faster in responding to information-bearing changes in the modulated ac signal.

Patent
28 Jun 1976
TL;DR: In this paper, an improved noise loading arrangement and method are disclosed capable of measuring low intensity intermodulaton distortion products, such as introduced in the operation of individual wideband transmission repeaters.
Abstract: An improved noise loading arrangement and method are disclosed capable of measuring low intensity intermodulaton distortion products, such as introduced in the operation of individual wideband transmission repeaters. The improved arrangement and method also have the further capability of resolving individual orders of distortion products. The arrangement utilizes a noise signal generator that produces a pseudorandom signal made of several spectral components providing high spectral density throughout a large bandwidth to simulate a broadband message load obtained by frequency multiplexing several independent signal sources. The noise signal is shifted in frequency before a quiet band is produced in the signal applied to the transmission apparatus to be tested. The orders of intermodulation distortion products appearing in the quiet band of the output signal of the transmission apparatus are individually measured to evaluate same. Automation of the test sequence is provided by a computer which acts as a general controller. The computer also processes the test data obtained by using a conventional signal averaging technique.

Patent
André Desblache1
15 Nov 1976
TL;DR: In this article, a new adaptive digital tuning filter for tracking a sinusoidal signal within a frequency band is described, in which the input signal representative of both the signal and noise is fed to a Hilbert transformer which provides the in-phase and quadrature components, x k and x k, respectively, of the signal.
Abstract: A new adaptive digital tuning filter for tracking a sinusoidal signal within a frequency band is described. The input signal representative of both said sinusoidal signal and noise is fed to a Hilbert transformer which provides the in-phase and quadrature components, x k and x k , respectively, of said sinusoidal signal. These components are applied to the input of a filter having a transfer function K where ##EQU1## WHERE φ = 2πFT, f is the tuned frequency of the filter, T is the signal sampling period and a is a constant close to unity. The output signals y x and y x of the filter are applied to a computing means which provides a frequency control signal e k such that e.sub.k = x.sub.k y.sub.k - y.sub.k x.sub.k The above value of φ is adjusted through a conventional gradient method where φ.sub.k + 1 = φ.sub.k + μe.sub.k and controls are provided to adjust φ in a direction to change e k toward zero. Application of the adaptive tuning filter to cancellation of the main component of phase jitter in a modem is also described.