Showing papers on "Background noise published in 1978"

All-pole modeling of degraded speech

Abstract: This paper considers the estimation of speech parameters in an all-pole model when the speech has been degraded by additive background noise. The procedure, based on maximum a posteriori (MAP) estimation techniques is first developed in the absence of noise and related to linear prediction analysis of speech. The modification in the presence of background noise is shown to be nonlinear. Two suboptimal procedures are suggested which have linear iterative implementations. A preliminary illustration and discussion based both on a synthetic example and real speech data are given.

Coded aperture imaging - Predicted performance of uniformly redundant arrays

Abstract: Uniformly redundant arrays (URA) have autocorrelation functions with perfectly flat sidelobes. The URA combines the high-transmission characteristics of the random array with the flat sidelobe advantage of the nonredundant pinhole arrays. A general expression for the signal-to-noise ratio (SNR) has been developed for the URA as a function of the type of object being imaged and the design parameters of the aperture. The SNR expression is used to obtain an expression for the optimum aperture transmission. Currently, the only 2-D URAs known have a transmission of (1/2). This, however, is not a severe limitation because the use of the nonoptimum transmission of (1/2) never causes a reduction in the SNR of more than 30%. The predicted performance of the URA system is compared to the image obtainable from a single pinhole camera. Because the reconstructed image of the URA contains virtually uniform noise regardless of the original object's structure, the improvement over the single pinhole camera is much larger for the bright points than it is for the low intensity points. For a detector with high background noise, the URA will always give a much better image than the single pinhole camera regardless of the structure of the object. In the case of a detector with low background noise, the improvement of the URA relative to the single pinhole camera will have a lower limit of ~(2f)(-(1/2)), where f is the fraction of the field of view that is uniformly filled by the object.

Amplitude-Probability Distribution Model for VLF/ELF Atmospheric Noise

Abstract: This paper presents an analytic model for VLF and ELF atmospheric-noise amplitude-probability distributions (APDs) The APDs are governed by two parameters that can be determined at the receiver-one characterizing the impulsivity of noise from local sources and the other characterizing the ratio of energy in the impulsive-noise component to the energy in the non-impulsive background-noise component The derived expression explicitly shows the dependence of the APD on the earth-ionosphere-waveguide propagation constant Calculated APDs are presented for ambient and nominally disturbed ionospheric conditions

Restoring with maximum entropy. III. Poisson sources and backgrounds

Abstract: The maximum entropy (ME) restoring formalism has previously been derived under the assumptions of (i) zero background and (ii) additive noise in the image. However, the noise in the signals from many modern image detectors is actually Poisson, i.e., dominated by single-photon statistics. Hence, the noise is no longer additive. Particularly in astronomy, it is often accurate to model the image as being composed of two fundamental Poisson features: (i) a component due to a smoothly varying background image, such as caused by interstellar dust, plus (ii) a superimposed component due to an unknown array of point and line sources (stars, galactic arms, etc.). The latter is termed the “foreground image” since it contains the principal object information sought by the viewer. We include in the background all physical backgrounds, such as the night sky, as well as the mathematical background formed by lower-frequency components of the principal image structure. The role played by the background, which may be separately and easily estimated since it is smooth, is to pointwise modify the known noise statistics in the foreground image according to how strong the background is. Given the estimated background, a maximum-likelihood restoring formula was derived for the foreground image. We applied this approach to some one-dimensional simulations and to some real astronomical imagery. Results are consistent with the maximum-likelihood and Poisson hypotheses: i.e., where the background is high and consequently contributes much noise to the observed image, a restored star is broader and smoother than where the background is low. This nonisoplanatic behavior is desirable since it permits extra resolution only where the noise is sufficiently low to reliably permit it.

Detection of Narrowband Signals Using Time-Domain Adaptive Filters

Abstract: The detection performance of a conventional narrowband analyzer is compared with two adaptive processor mechanizations based on the Widrow least mean squares algorithm. Comparisons are based on both analysis and extensive digital simulation. With a narrowband signal in stationary, white background noise, the performance of the three systems is shown to be essentially the same. With nonstationary background noise, the performance of the conventional system degrades by an amount proportional to the processing time-bandwidth product. The adaptive systems appear to be less sensitive to the nonstationary background, resulting in a potential performance advantage relative to the conventional system.

InSb charge-injection device imaging array

Abstract: InSb CID arrays, in both 1 × 32 line and 16 × 24 two-dimensional format, have been successfully fabricated via a multilayer MIS processing technique. With the 1 × 32 line arrays, two-dimensional images were generated using a scanning mirror and a computer signal-conditioning technique. In this experiment the small temperature difference of a man's face was revealed. Two-dimensional, 16 × 24 area arrays have also been demonstrated in a staring mode by displaying real time raster-scanned IR images directly on a X-Y CRT monitor. The unprocessed IR video signal produced a sharp, clearly recognizable display with no sign of blooming, and exhibited excellent operating characteristics. Theoretical analysis showed that, at low sample rates, background limited performance (BLIP) can be obtained at background photon flux levels of as low as mid-1012photons/s . cm2. The dominant noise source, in this case, is the integrated dark current shot noise. For operation at high sample rates, however, the bandwidth-dependent noise sources limit the array performance and, thus, BLIP occurs at higher background levels. The analysis has been confirmed by measured data on line arrays, resulting in good agreement between the theoretical curve and the experimental data.

Center and limb solar spectrum in high spectral resolution 225.2 nm to 319.6 nm

Abstract: The atlas has been designed to fulfill the need in solar and stellar astronomy, in aeronomy, and in space science for a convenient reference source that provides a detailed and accurate record of the measured solar ultraviolet spectrum in high spectral resolution for the wavelength range from 2252 nm to 3196 nm The atlas also contains a preliminary synthetic solar spectrum with a legend for identifying and describing the features of the synthetic spectrum Attention is given to aspects of instrumentation, the radiometric calibration, the wavelength scale, background noise random fluctuations and data filtering, intermittent noise, the observational conditions, the experimental uncertainty, the atlas format, references, tables, and plots

Linear flaw detector

Abstract: A linear flaw detector for coated surfaces. An incident beam is provided and sensed above and below the theoretical specular angle. Where a flaw occurs, the reflected signal changes in intensity. By sensing above and below the specular angle, the signal corresponding to the flaw is accented in reference to the signals from the background. The signal corresponding to the flaw may then be separated from background noise and an output provided.

Maximum likelihood estimation of the number, directions and strengths of point radio sources from variable baseline interferometer data

Abstract: The optimum estimation of the number, directions, and strengths of multiple point radio sources is considered when the mutual coherence function of the sources' radiation is spatially sampled at M baselines by a variable baseline correlation interferometer. The measurements are corrupted by the effects of additive background noise (including receiver noise) and a finite correlation time. Statistically approached, the problem is considered as a combination of parameter estimation and goodness of fit with the maximum likelihood (ML) principle being the basic criterion used. First the measurements' probability density function is derived, assuming the sources' number is known. Then the ML estimator (MLE) of the sources' parameters is obtained. The MLE's asymptotic optimum performance (unbiasedness with minimum variance) is then shown to be achieved when the number of measurements exceeds the number of sources by a threshold that is small (or zero) for most signal-to-noise ratios of interest. Next the number of sources is estimated according to a likelihood probability that measures the tenability of the MLE associated with every possible number of sources with respect to the measurements. The ML number-parameter estimation theory is then put into the form of an efficient algorithm which proves to be superior when compared to other processing methods such as Fourier maps.

Suppression of noise in speech using the saber method

Abstract: A stand alone noise suppression algorithm is described for reducing the spectral effects of acoustically added noise in speech. A fundamental result is developed which shows that the spectral magnitude of speech plus noise can be effectively approximated as the sum of magnitudes of speech and noise. Using this simple phase independent additive model, the noise bias present in the short time spectrum is reduced by subtracting off the expected noise spectrum calculated during nonspeech activity. After bias removal, the time waveform is recalculated from the modified magnitude and saved phase. This Spectral Averaging for Bias Estimation and Removal, or SABER method requires only one FFT per time window for analysis and synthesis.

Terrain Considerations and Data Base Development for the Design and Testing of Devices to Detect Intruder-Induced Ground Motion

Abstract: : This study attempted to develop a readily accessible body of information that defines the ranges of intruder signal characteristics within which seismic sensors for intruder detection, classification, and location must operate. The principal product of the study was a data base of seismic signatures (recorded on magnetic tape) that contains representation of the range of target types, travel modes, terrains, and background noise sources that can realistically be expected to occur for base and installation environments and in operational scenarios. Both an experimental and a theoretical approach were taken. The first approach consisted of collecting and analyzing the signatures of intruders and background noise sources in a wide range of terrain conditions (as determined from bulk properties describing the compression and shear strength of the media, moisture, density, etc.). The theoretical approach consisted of applying mathematical models of the seismic signature generation and propagation phenomena so as to extend the data base of seismic signatures to include terrain conditions not represented in the data collection portion of the work. The mathematical models were also used to evaluate site documentation procedures and to estimate the frequency of occurrence of groups of terrains for which similar signature characteristics can be expected to occur.

Speech intelligibility enhancement in a power generating noise environment

Abstract: A previous paper described a method for processing speech which resulted in the enhancement of speech intelligibility in the presence of high noise levels at the listener. This processing technqiue consists of high-pass filtering followed by rapid amplitude compression. A significant intelligibility gain was achieved over unprocessed speech for signal-to-noise ratios from -10 to +10 dB (noise at 90 dB). In this previous work, only white noise was considered. In the present paper, results are presented for this processing technique for a listener in the environment of power generating noise.

Acoustic emission contact fuze with signal processing capability

Abstract: An acoustic emission contact fuze that is responsive to high-frequency actic emission stress waves and distinguishes between such waves caused by impacts and signals caused by the operating environment.

Background noise levels and heart rate orienting: response detection using time series analysis.

Abstract: The purpose of this paper is two-fold. The first is to introduce a method of analyzing single trials of beat-to-beat heart rate in adult subjects, by which significant changes in heart rate following a stimulus may be detected. The second is to demonstrate the economy of this form of analysis by presenting it in the context of a small-scale experiment. The experiment examined heart rate orienting responses to a standard auditory signal, comparing the effects of high and low continuous background noise. The higher background noise level was found to enhance the accelerative component of the heart rate response to auditory signals.

High resolution spectral analysis of sinusoids in correlated noise

Abstract: A high resolution technique for estimating the frequencies, powers, and the number of sinusoids in noise is examined. Unlike the Pisarenko decomposition method which may only be applied to sinusoids in uncorrelated noise, the technique examined in this paper may be applied even when the noise is correlated. This technique consists of applying Prony's algorithm to a segment of the autocorrelation function, r(k), for which |k| is greater than Γ corr , where Γ corr is the decorrelation time of the noise.

The ODCAT: One Dimensional Coded Aperture Tomography

Abstract: Current emission computed tomographic (ECT) scanners suffer from the inability to perform dynamic studies. The investigation presented here was initiated with a specific goal in mind, that is, to design a system to image a radionuclide distribution in cross-section in a stationary arrangement capable of dynamic data acquisition. Two systems are proposed. Both systems utilize a two-dimensional cross-section type of geometry. The first consists of multiple pinhole apertures each with its own separate one-dimensional detector. The second system employs coded-aperture techniques and is a result of allowing the projections from each pinhole aperture to overlap. The initial reconstructed image with both systems is degraded by a high level of correlated background noise. This background is significantly reduced by an iterative subtraction technique which is described. Computer simulations are presented to illustrate the technique.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Linear prediction and maximum entropy spectral analysis of finite bandwidth signals in noise

Abstract: The optimal minimum-mean-square-error discrete filters are obtained for finite bandwidth signals in noise represented by a rational pole-zero model in the spectral domain. An analytical technique called the method of undetermined coefficients is used to solve the Wiener equation for the optimal prediction coefficients. These coefficients are then used to examine (a) the frequency response of the Wiener prediction filter, and (b) the maximum entropy spectral estimator. Special cases considered include the limiting case of narrow bandwidth signals and large prediction filter lengths.

High quality adaptive predictive coding of speech

Abstract: We report on the results of research to code speech at 16 kbps under the condition that the quality of the transmitted speech be equal to that of the original. Some of the original speech had been corrupted by noise and distortions typical of long distance telephone lines. The rigorous requirements of this work led to a new outlook on adaptive predictive coding. We have found that the pitch predictor is not useful on balance and should be eliminated, and that the residual should be quantized with no clipping and encoded using a variable-length code. A single coding scheme seems to be adequate for all speech and all conditions. In addition, the adaptive predictive coding system has been modified to include a noise spectral shaping filter that effectively eliminates the perception of background granular noise.

Status of Some Current Research in Jet Noise

Abstract: A review is presented of the status of jet noise technology and suppression concepts being pursued. The current ability of predicting noise from jets is discussed, and some aspects of jet noise suppression are dealt with. Particular attention is given to the problem of inflight effects on jet noise suppressors which still remains a critical issue.

Intensity and predictability of background noise as determinants of simple reaction time

Abstract: This research permits a comparison of the effects of background-noise intensity (105 dB, 70 dB, and no noise) and mode of presentation (unpredictable, predictable, and self-administered) on simple reaction time (RT) to auditory and visual test signals. Each of 112 subjects participated in a 1-h session comprised of 146 RT trials. The background noise was presented during the intertrial interval, and the average exposure duration was 2 sec/trial. It was found that at 105-dB noise levels, intensity was the crucial variable, whereas at 70-dB levels, the predictability of the background noise was of primary importance. It was concluded that background noise debilitates RT performance when the noise is too loud, or, if the noise is moderately intense, because it is temporally unpredictable.

Noise temperature in GaAs epi-layer for FET's

Abstract: The noise temperature field-dependent relationship was experimentally investigated in thin GaAs epi-layer. It was found that the commonly used relationship is inaccurate for most of the devices. A new relationship of extended, validity was derived in the lattice temperature 90-370 K.