Showing papers on "Noise measurement published in 1976"

An efficient method for computer aided noise analysis of linear amplifier networks

Abstract: A method for computer aided noise analysis is presented which is based on a description of noise by means of correlation matrices. The method is a two-port analysis and it is, therefore, applicable to circuits which are composed of simple two-ports with known noise performance. The correlation matrix concept holds two main advantages over other methods of noise analysis. Partially correlated noise sources can be treated without any loss of efficiency and information concerning minimum noise figure and noise matching conditions is obtained.

Image Restoration Based on a Subjective Criterion

Abstract: The problem of removing random noise from gray tone images without significantly sacrificing the subjective resolution is considered. Based on a subjective visibility function, which gives the relationship between the visibility of a unit noise and a measure of local spatial detail (spatial masking), two procedures are developed to adapt continuously the finite impulse response of a two-dimensional, noncausal, linear digital filter. At sharp transitions in the image intensity, the filter operator is strongly peaked to preserve the resolution, whereas in flat areas it is flat to effectively average out the random noise. The first procedure (S-filter) is computationally more efficient, but does not perform as well as the second method (SD-filter) which requires solution of a new optimization problem at every picture element. Results of several simulations are presented to demonstrate the feasibility of our approach. Extensions are pointed out to incorporate different adaptation procedures and psychovisual criteria other than the type of spatial masking used here.

The Detection of Signals in Impulsive Noise Modeled as a Mixture Process

Abstract: A first-order mixture noise density is considered as a model for impulsive noise channels It consists of a mixture of a small variance, probably Gaussian, background noise pdf and a large variance impulsive pdf Optimal nonlinear detector structures for known discretetime signals in such noise are derived Their large-sample performance compared to that of a linear detector is studied using asymptotic relative efficiency

Method of and means for adaptively filtering near-stationary noise from speech

Abstract: By identifying and analyzing the properties of the parameters of an input signal that contains speech in the presence of simultaneously occuring near-stationary noise, pauses between speech intervals as well as the termination of such noise can be recognized. When a pause interval containing noise is recognized, the parameters identified during such interval are used to set the parameters of an adaptive filter through which the input signal is passed during subsequent intervals of speech and until the noise terminates. During the time the input signal passes through the filter, the near-stationary noise is filtered out. In response to recognition of the termination of noise, the input signal is caused to by-pass the filter which is then prepared to accept the parameters of noise occuring in a subsequent pause.

Roundoff noise in state-space digital filtering: A general analysis

Abstract: A new noise expression is formulated for the class of fixed-point digital filters described by the state equations, and two methods of its computation are discussed. The effects of possible structure transformation and state-amplitude scalings are then incorporated in this expression, and the results have been analyzed. In particular, it is shown that the output noise and state amplitudes are inversely proportional, and that an elementary transformation is well suited for a step-by-step generation of a low-noise filter.

On Optimal Control of Linear Systems in the Presence of Multiplicative Noise

Abstract: This correspondence considers the problem of optimal regulator design for discrete time linear systems subjected to white state-dependent and control-dependent noise in addition to additive white noise in the input and the observations. A pseudo-deterministic problem is first defined in which multiplicative and additive input disturbances are present, but noise-free measurements of the complete state vector are available. This problem is solved via discrete dynamic programing. Next is formulated the problem in which the number of measurements is less than that of the state variables and the measurements are contaminated with state-dependent noise. The inseparability of control and estimation is brought into focus, and an "enforced separation" solution is obtained via heuristic reasoning in which the control gains are shown to be the same as those in the pseudo-deterministic problem. An optimal linear state estimator is given in order to implement the controller.

Noise in buried channel charge-coupled devices

Abstract: In this paper we discuss the noise measured at the output of a buried channel charge-coupled device (BCCD) linear shift register. The measured noise arises from four sources; the electrical insertion of signal charge, the output amplifier, dark current, and bulk state trapping. In making these measurements the concept of correlated double sampling was used in an output circuit which had a noise level which was equivalent to less than 3O noise electrons. A critical component in this output was a low noise MOSFET which was achieved by use of the buried channel technology. A low noise input structure for electrical insertion of signal charge was used which introduced a signal which had a noise level which ranged from less than 10 e-to as high as 60 e-depending on the size of the signal charge. The dark current noise was found to be well characterized as a shot noise and levels on the order of 20 e-were measured. The above low noise levels made possible direct measurement of the noise due to bulk state trapping, and depending on the signal size and clock rate noise levels were measured which ranged from less than 10 to over 100 noise electrons. One of the most important bulk traps was found to be due to gold impurities which had a density of ∼ 2 × 1011cm-3.

Noise filtering device

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.

Performance of GaAs MESFET's at Low Temperatures (Short Papers)

Abstract: The noise- and s-parameters of a GaAs MESFET with 1-mu m gate Iength are characterized versus temperature. At room temperature, the noise figure measured at 12 GHz is 3.5 dB. At 90 K, the noise figure decreases to 0.8 dB (T/sub e/ = 60 K). The associated gain is 8 dB. The design of a cooled amplifier for the 11.7-12.2-GHz communication band is discussed. At 60 K, the three-stage amplifier exhibits 1.6-dB noise figure (T/sub e/ = 130 K) and 31-dB gain.

Noise characterization of linear circuits

Abstract: The noise characterization of linear circuits is discussed in connection with the transformation of the noise parameters. The noise performance of two-ports is treated, as are methods for linear devices including correlated, uncorrelated, and partially correlated noise sources. Finally, the experimental determination of the noise parameters is described. Special attention is given to negative source resistances. It is shown that the noise performance of any linear two-port network can be completely characterized by 12 parameters; four noise and four complex network parameters.

Background noisemasking system

Abstract: Noisemasking speakers are positioned in an array to direct noise into a space which is to be used by a number of people so that individual privacy is assured. The array is divided into four or more sets of speakers. The single noise source is equalized, and the same equalized noise is fed to the four speaker sets through time-delay devices so that the noise from each set has low correlation with each of the other sets.

A Multivariate Statistical Pattern Recognition System for Reactor Noise Analysis

Abstract: A multivariate statistical pattern recognition system for reactor noise analysis was developed. The basis of the system is a transformation for decoupling correlated variables and algorithms for inferring probability density functions. The system is adaptable to a variety of statistical properties of the data, and it has learning, tracking, and updating capabilities. System design emphasizes control of the false-alarm rate. The ability of the system to learn normal patterns of reactor behavior and to recognize deviations from these patterns was evaluated by experiments at the ORNL High-Flux Isotope Reactor (HFIR). Power perturbations of less than 0.1% of the mean value in selected frequency ranges were detected by the system.

On noise in digital recording

Abstract: A set of rules, equations and relations are given for the effects of coherent and statistical noise on digital recorders. Simple formulas, intended for laboratory use, are given for the change in signal to noise ratio (SNR) caused by the channel. Bit error probability is related to SNR and channel parameters for the zero-crossing detector channels typical of digital computer disk and tape recorders, and many digital instrumentation recorders. Valid and invalid ways to calculate error rate statistics are discussed for situations where bit errors are correlated, i.e. not statistically independent.

Use of Low-Pass Noise in Word-Recognition Testing

Abstract: This study attempted to determine whether word-recognition scores obtained in noise were more sensitive to the presence of a hearing loss than recognition scores obtained in quiet. Subjects with no...

Direct measurement techniques of transmission line corrections for thermal noise standards

Abstract: A thermal noise source consists of a matched termination and a transmission line. A method which permits a direct measurement of the correction due to the transmission line effects on the thermal noise source without any measurement of temperature, loss, and reflection distribution in the transmission line is presented. Generalised expressions for the equivalent temperature of the thermal noise source are derived, which are composed of the temperature of the matched termination, the output reflection coefficient, and the transmission corrections. It is shown that the corrections can be determined from reflection coefficients and noise outputs of the source in which the matched termination is replaced by a short. A possibility is suggested, that higher accuracy in the correction will be obtained by the new method than by conventional ones. A 10-GHz noise source is tested by the method.

Detection in image dependent noise (Corresp.)

Abstract: The detection of two-dimensional optical signals which have been corrupted by noise is considered. Discussion is limited to the detection of a known object in a known location. The problem is approached from the classical statistical technique of hypothesis testing. Initially the solution is formulated in very general terms. The decision rule is derived for a signal distorted by noise of an unspecified type which may include signal dependent noise. Once the decision rule is obtained, the probabilities of false alarm and detection are evaluated from a {\sl a priori} knowledge of the noise and imaging system. The general results are applied to Poisson noise, signal dependent Gaussian noise, and binomial noise.

Measurement, analysis, and prediction of aircraft interior noise

Abstract: Considerations of comfort of passengers and crew in light aircraft and helicopters indicate substantial benefits may be obtained by the reduction of interior noise levels. This paper discusses an ongoing research effort to reduce interior noise in such vehicles. Data from both field and laboratory studies for a light aircraft are presented. The laboratory data indicate that structural vibration is an efficient source of interior noise and should be considered in the reduction of interior noise. Flight data taken on a helicopter before and after installation of acoustic treatment demonstrate that over 30 dB of noise reduction can be obtained in certain portions of the spectra. However, subjective evaluations of the treated vehicle indicate that further reductions in interior noise are desirable. An existing interior noise prediction method which was developed for large jet transports was applied to study low-frequency noise in a light aircraft fuselage. The results indicate that improvements in the analytical model may be necessary for the prediction of interior noise of light aircraft.

Amplitude probability distribution measurements at the apple grove 775 kV project

Abstract: As part of the Radio Interference (RI) meter-comparison tests at the AEP-Westinghouse Apple Grove 775 kV Project in Apple Grove West Virginia, October 1974, Amplitude Probability Distribution (APD) measurements were made of the wet and dry conductor corona and gap radio noise processes. This paper describes the equipment and methods used for the measurements. From the APD data it is shown that values for the V rms , V average and V d noise parameters may be calculated and that these agree favourably with the values of the same parameters measured on meters having the same bandwidths. Finally it is shown that from values of the V rms and V d noise parameters it is possible to predict the APD with good results by using the CCIR and Log-Normal noise models previously developed for atmospheric noise.

Radio source parameter estimation by maximum likelihood processing of variable baseline correlation interferometer data

Abstract: The accurate joint determination of the direction and strength of a point noise source when the mutual coherence function of its radiated field is spatially sampled at M baselines by a correlation interferometer is considered. The measurements are corrupted by the combined effects of a) the additive background and receiver noises at the interferometer antennas and b) the finite integration time of a practical correlator. The problem is approached from a statistical point of view (as contrasted with beam forming techniques). First the probability density function of the measurements is derived. The source's two parameters (direction and strength) are then jointly estimated using the maximum likelihood (ML) method. Investigation of the estimates' properties shows that they are virtually unbiased with variances that effectively attain the standard Cramer-Rao (C-R) lower bound when the number of measurements exceeds a "threshold" which is a decreasing function of the measurements' signal-to-noise ratio (SNR). The empirically observed fact that such a threshold is quite small, even at low SNR's, as well as the unbiasedness of the estimates, makes the performance of these (ML) estimates optimum for most practical applications.

A versatile pseudo-random noise generator

Abstract: A detailed design is presented for a digital pseudo-random noise generator. The instrument is built with standard integrated circuits. It produces both binary noise (pseudo-random binary sequence) and white Gaussian noise of variable bandwidth. By setting front panel switches to match tabulated octal codes, one may select a vast number of independent noise programs.

Random rounding: Some principles and applications

Abstract: Truncation and rounding operations in digital signal processing introduce harmonic and intermodulation distortion for low level inputs or pure signal inputs. A two step random rounding procedure alleviates these problems by introducing "white" quantization noise. Some results bearing on the quantization noise levels as a function of input level and on linearity are presented. In one application a simple recursive integrator is found to have dramatic correlated quantization error affects unless random rounding is employed.

Means for distinguishing motion from noise in an intrusion alarm system

Abstract: Composite noise and information signals are amplified and filtered to segregate high and low frequency bands that correspond with noise from an intermediate frequency band which corresponds with the information signal. The absolute values of the two noise band signals are summed, weighted, and compared with the information band signal in an operational amplifier whose output tends toward a signal of one polarity with respect to a reference voltage due to noise and tends toward the opposite polarity due to the information band frequency. The signal is integrated and used to control an alarm circuit and environmental noise indicating devices. Means are provided to reduce sensitivity of one of the devices in the presence of high noise and to restore sensitivity if a valid information signal occurs. The other device is used to warn of persistent environmental noise that might be eliminated. The input amplifier of the system is provided with a feedback circuit that brings about compressor action to null the effect of high transient noises.

Sources and characteristics of interior noise in general aviation aircraft

Abstract: A field study has been conducted to examine the interior noise characteristics of a general aviation aircraft. The purposes of the study were to identify the major noise sources and their relative contribution and to establish the noise transmission paths and their relative importance. Tests were performed on an aircraft operating under stationary conditions on the ground. The results show that the interior noise level of light aircraft is dominated by broadband, low frequencies (below 1,000 Hz). Both the propeller and the engine are dominant sources; however, the contribution from the propeller is significantly more than the engine at its fundamental blade passage frequency. The data suggests that the airborne path is more dominant than the structure-borne path in the transmission of broadband, low-frequency noise which apparently results from the exhaust.