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Showing papers on "Signal-to-noise ratio published in 1979"


Proceedings ArticleDOI
02 Apr 1979
TL;DR: This paper describes a method for enhancing speech corrupted by broadband noise based on the spectral noise subtraction method, which can automatically adapt to a wide range of signal-to-noise ratios, as long as a reasonable estimate of the noise spectrum can be obtained.
Abstract: This paper describes a method for enhancing speech corrupted by broadband noise. The method is based on the spectral noise subtraction method. The original method entails subtracting an estimate of the noise power spectrum from the speech power spectrum, setting negative differences to zero, recombining the new power spectrum with the original phase, and then reconstructing the time waveform. While this method reduces the broadband noise, it also usually introduces an annoying "musical noise". We have devised a method that eliminates this "musical noise" while further reducing the background noise. The method consists in subtracting an overestimate of the noise power spectrum, and preventing the resultant spectral components from going below a preset minimum level (spectral floor). The method can automatically adapt to a wide range of signal-to-noise ratios, as long as a reasonable estimate of the noise spectrum can be obtained. Extensive listening tests were performed to determine the quality and intelligibility of speech enhanced by our method. Listeners unanimously preferred the quality of the processed speech. Also, for an input signal-to-noise ratio of 5 dB, there was no loss of intelligibility associated with the enhancement technique.

1,352 citations


Journal ArticleDOI
TL;DR: In this paper, a general expression for the signal-to-noise ratio of a heterodyne lidar system in the presence of atmospheric turbulence is derived which is valid both in the near and far-field of the laser and remoted scattering source.
Abstract: A general expression for the signal-to-noise ratio of a heterodyne lidar system in the presence of atmospheric turbulence is derived which is valid both in the near- and far-field of the laser and remoted scattering source. We consider the situation where a laser transmitter directs an optical beam at some remote scattering region of interest. The backscattered light is collected by a receiving aperture and mixed with a suitable coherent local oscillator reference field. Both coaxial and bistatic lidar systems are considered. In both cases we are able to obtain algebraic expressions for the signal-to-noise ratio which are valid for an arbitrary propagation path through the atmosphere. Numerical results are presented for both a 3.7 and 10.6 micrometer lidar system. Additionally, we obtain the conditions under which atmospheric turbulence will limit severely the performance of heterodyne lidar systems.

80 citations


Journal ArticleDOI
TL;DR: In this article, an adaptive antenna array can achieve an angular resolution of uncorrelated interference sources substantially greater than the aperture of diffraction limit by using adaptive techniques, where the antenna beam is scanned over the interference source locations and for each scan condition the adaptive processor is allowed to reach its steady state.
Abstract: By using adaptive techniques an antenna array can achieve an angular resolution of uncorrelated interference sources substantially greater than the aperture of diffraction limit. The antenna beam is scanned over the interference source locations, and for each scan condition the adaptive processor is allowed to reach its steady state. It is shown that for realistic ratios of interference strengths to system thermal noise, resolutions in excess of 0.25 times the Rayleigh limit can be achieved.

78 citations


Proceedings ArticleDOI
01 Dec 1979
TL;DR: In this paper, an extended Kalman filter is proposed to estimate the translational position changes of the target in the FLIR field of view due to two effects: actual target motion and apparent motion caused by atmospheric turbulence.
Abstract: An extended Kalman filter algorithm is designed to track a point source target in an open-loop tracking problem, using outputs from a forward-looking infrared (FLIR) sensor as measurements. The filter separately estimates the translational position changes of the target in the FLIR field of view due to two effects: actual target motion and apparent motion caused by atmospheric turbulence. A Monte Carlo analysis is conducted to determine the performance of the filter as a function of signal-to-noise ratio, target spot size, the ratio of rms target motion to rms atmospheric jitter, target correlation times, and mismatches between the true target spot size and the size assumed by the filter. The performance of the extended Kalman filter is compared to the performance of an existing correlation tracker under identical conditions. A one sigma tracking error of 0.2 and 0.8 picture elements is obtained with signal-to-noise ratios of 20:1 and 1:1, respectively. No degradation in performance is observed when the spot size is decreased or when the target correlation time is increased over a limited range, when filter parameters are adjusted to reflect this knowledge. Sensitivity analysis shows that the filter is robust to minor changes in target intensity spot size.

51 citations


PatentDOI
TL;DR: Space variant optical processors using coordinate transformations and a new phase detection scheme are used to realize multiple invariant optical correlators that are invariance to more than one distortion parameter per axis of the processor.
Abstract: A multiple-invariant, space variant optical processor in which two functions described by any number of separate distortion parameters can be correlated with no loss in signal-to-noise ratio of the correlation. The unknown distortion parameters can also be determined in this scheme. Experimental confirmation of the key step, determination of the non-linear phase portion of a complex optical transform can be provided.

32 citations


Proceedings ArticleDOI
20 Aug 1979
TL;DR: In this paper, a least-mean-square filter technique is defined for signal detection problems in a scanning infrared surveillance system operating in poorly characterized but primarily low-frequency noise clutter environments.
Abstract: A new least-mean-square filter technique is defined for signal detection problems. The technique is applied to a scanning infrared surveillance system operating in poorly characterized but primarily low-frequency noise clutter environments. Near optimal performance is predicted both for continuous time and sampled data systems.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

22 citations


Journal ArticleDOI
TL;DR: In this paper, the problem of simultaneously determining the midpoint position, separation, and relative intensities of a pair of closely spaced point sources has been studied, and a generalized expression that allows calculations of the resolution scale from the optical-signal transfer function of the system is given.
Abstract: We have studied the problem of simultaneously determining the midpoint position, separation, and relative intensities of a pair of closely spaced point sources. Our objective has been to see how the signal-to-noise ratio affects the measurement precision and to determine the significance of the various optical-system design parameters, and from this to develop a concept of resolution relevant to the generalized resolution problem, as posed by Ronchi over a decade ago. General results have been obtained for a scanning sensor designed to produce a one-dimensional output signal, with additive Gaussian noise. The rms precision with which the position of a single target can be measured has been determined. From this, we have obtained a resolution scale that, when divided by the signal-to-noise (voltage) ratio, gives the noise-limited position-measurement precision. A generalized expression that allows calculations of the resolution scale from the optical-signal transfer function of the system is given. Results in generalized form are developed for the precision with which the separation, midpoint position, and relative intensity of a pair of point sources can be measured. These results are presented in terms of the modulation transfer function of the optics and of the detector, and of the noise power spectrum. Quantitative results have been calculated for a system that consists of diffraction-limited, unobscured-circular-aperture optics and a sharply delineated rectangular detector, with additive white Gaussian noise. The numerical results show that the resolution scale is apparently also a significant descriptor of the two-target measurement capabilities of the instrument. This suggests that the resolution scale ought to be considered the resolution of. an instrument—to the extent that any single number can be used to define the resolution of an instrument.

22 citations


Journal ArticleDOI
TL;DR: In this article, analytical and simulation methods are employed to determine the balance between coherent and non-coherent integration that yields the greatest SNR improvement in a model using peak selection of fast Fourier transform Doppler channels.
Abstract: Modern radars may incorporate pulse-to-pulse carrier frequency modulation to increase probability of detection, to reduce Vulnerability to jamming, and to reduce probability of interception. However, if coherent processing is used for clutter rejection, the frequency of N consecutive pulses must be held constant for N-pulse clutter cancellation or Doppler filtering. If M pulses are transmitted during the time the antenna illuminates a target, there are M/N coherently integrated echoes available for noncoherent integration in the computer or the operator's display to further improve the signal-to-noise ratio (SNR). In this paper, analytical and simulation methods are employed to determine the balance between coherent and noncoherent integration that yields the greatest SNR improvement. Attention is focused upon a model using peak selection of fast Fourier transform (FFT) Doppler channels and is compared to a reference model involving only a single Doppler channel. Curves of detectable SNR as a function of M and N are presented for both models.

16 citations


Patent
26 Feb 1979
TL;DR: In this paper, a digital signal receiver translates pulse code modulated (PCM) tone signalling into a signal format compatible with a controller in an associated time division multiplex (TDM) telephone switching facility.
Abstract: A digital signalling receiver translates pulse code modulated (PCM) tone signalling into a signal format compatible with a controller in an associated time division multiplex (TDM) telephone switching facility. In the receiver, steering signals are generated in synchronism with the operation of the switching facility to direct the operation of a time shared filter. The filter performs a plurality of filter functions with a series of PCM signals received from the TDM switching facility and generates therefrom series of filter signals relative each of the filter functions. A translator identifies two filter signals having larger amplitudes than the others and if the two signals persist substantially uninterrupted (a) through a predetermined period of time, (b) within a predetermined relative amplitude range and (c) one of the two signals having at least a predetermined signal to noise ratio relative another filter signal corresponding to an allpass filter function, the translator indicates the receipt of multifrequency signalling by generating the appropriate signals in the required signal format.

16 citations


Journal ArticleDOI
TL;DR: A general formula for the calculation of the signal to noise ratio (SNR) of a spectroscopic measurement is derived, and its factors are discussed.
Abstract: A general formula for the calculation of the signal to noise ratio (SNR) of a spectroscopic measurement is derived, and its factors are discussed. Particular attention is paid to identify which losses are necessarily present in the measurement and which can be avoided or reduced. The formula can also be used for the comparison of the different spectroscopic methods.

15 citations


Proceedings ArticleDOI
02 Apr 1979
TL;DR: A study of the filter length required to achieve a desired noise reduction level in a hard-walled room is presented and results demonstrating noise reduction in excess 10dB in an environment with 0dB signal noise ratio are presented.
Abstract: Nonstationary acoustic noise with energy possibly equal to or greater than the speech is suppressed using a two microphone implementation of adaptive noise cancellation. The primary noise added to the speech is reduced by subtracting a filtered version of the second microphone reference noise. The reference noise filter is adaptively up dated using the Widrow-Hoff LMS algorithm [1]. The effectiveness of noise suppression depends directly on the ability of the filter to estimate the transfer function relating the primary and reference noise channels. A study of the filter length required to achieve a desired noise reduction level in a hard-walled room is presented. Results demonstrating noise reduction in excess 10dB in an environment with 0dB signal noise ratio are presented.

01 Jan 1979
TL;DR: In this paper, the spectral response functions observed from a stratum were modeled as a stochastic process with a Gaussian probability measure, and the performance of the overall recognition system was studied relative to the accuracy of the spectral representation.
Abstract: The author has identified the following significant results. In order to choose a design which will be optimal for the largest class of remote sensing problems, a method was developed which attempted to represent the spectral response function from a scene as accurately as possible. The performance of the overall recognition system was studied relative to the accuracy of the spectral representation. The spectral representation was only one of a set of five interrelated parameter categories which also included the spatial representation parameter, the signal to noise ratio, ancillary data, and information classes. The spectral response functions observed from a stratum were modeled as a stochastic process with a Gaussian probability measure. The criterion for spectral representation was defined by the minimum expected mean-square error.

Journal ArticleDOI
TL;DR: The experiments of Kotera et al. as mentioned in this paper on InSb thin-film Hall elements can be interpreted with existing noise calculations on four-probe configurations, which can be found in Table 1.
Abstract: The experiments of Kotera et al. on InSb thin‐film Hall elements can be interpreted with existing noise calculations on four‐probe configurations.

ReportDOI
01 Jun 1979
TL;DR: In this paper, an optimal filter in the sense of maximum a posteriori probability (MAP) is derived for image signals detected at low light levels, where the emission of photons is described by a Poisson point process, with the average rate of emission proportional to the integrated intensity.
Abstract: : An optimal filter in the sense of maximum a posteriori probability (MAP) is derived for image signals detected at low light levels. These signals suffer from Poisson noise and blurring degradations. The low level photon resolved image signal is modeled as an inhomogeneous Poisson point process. The photon noise is inherent in any detected image, and is particularly serious at low light levels. At these low light levels, the emission of photons is described by a Poisson point process, with the average rate of emission proportional to the integrated intensity. The blurring degradation model in the system includes space-variant and space-invariant effects uch as atmospheric turbulence, linear motion, diffraction, and aberrations. The estimation is performed assuming that the photon events counted in each detector are independent, Poisson distributed random processes for the large time-bandwidth product case.

Journal ArticleDOI
TL;DR: A solution for the output signal-to-noise ratio of a bandpass nonlinearity which is attractive for numerical evaluations of certain nonlinearities of interest is presented.
Abstract: This paper presents a solution for the output signal-to-noise ratio of a bandpass nonlinearity which is attractive for numerical evaluations of certain nonlinearities of interest. The solution is obtained by solving a differential equation which results in an expression for the n th order Chebyshev transform of an odd-order nonlinearity in terms of the (n - 1) st-order Chebyshev transform of the derivative of the nonlinearity. The particular cases treated included a linear-logarithmic amplifier, an arctangent limiter, and a piecewise-linear limiter. The approach and results are related to previous efforts.

Journal ArticleDOI
TL;DR: In this paper, an expression for the statistical uncertainty at a point in the summed spatial autocorrelation functions of a finite number of photon limited images is derived for the point-wise signal to noise ratio in speckle interferometry for binary and giant stars.

Proceedings ArticleDOI
01 Jan 1979
TL;DR: In this article, a non-conventional acoustical type of underwater sound detector utilizing surface acoustic wave (SAW) resonator controlled oscillators is described, where the output variable is a frequency offset from a reference oscillator.
Abstract: A non-conventional acoustical type of underwater sound detector utilizing surface acoustic wave (SAW) resonator controlled oscillators is described. Unlike ceramic baseband transducers, the output variable is a frequency offset from a reference oscillator. The SAW sensor is comparable to conventional baseband sensors with a sensitivity of -180 dB re 1 V/uPa. Experimental sensors are described and characterized in terms of noise floor, signal to noise ratio, and frequency response. Using a SAW resonator controlled oscillator results in maximlm stability and hence a minimum noise floor. In addition a minimum of circuit grain required foroscillation minimizes the amount of power consumed by the sensor circuitry.

PatentDOI
TL;DR: In this article, the p-bit memory is sequentially addressed with each stored sample being suitably scaled for reestablishing the magnitudes of the corresponding n-bit samples, the scaled samples being coupled through a digital to analog converter for producing an output signal representing the percussive waveform and having a uniform signal to quantizing noise ratio.
Abstract: An electronic musical instrument includes a p-bit memory sequentially storing the resolution contributing bits of a sequence of n-bit samples, the n-bit sequence representing a percussive-type waveform. The p-bit memory is sequentially addressed with each stored sample being suitably scaled for reestablishing the magnitudes of the corresponding n-bit samples, the scaled samples being coupled through a digital to analog converter for producing an output signal representing the percussive waveform and having a uniform signal to quantizing noise ratio.


Journal ArticleDOI
TL;DR: In this article, the signal-to-noise ratio for interferometers using collector areas large compared to the correlation length of atmospherically distorted wavefronts is derived.
Abstract: The signal-to-noise ratio for long-baseline stellar interferometers is evaluated. Results are derived for interferometers using collector areas large compared to the correlation length of atmospherically distorted wavefronts. Analysis is given for interferometers which interfere images of the object or images of the collector pupils and for situations where the result is taken point by point or spatially averaged with signal dependent or signal independent weighting functions. Using a complex gaussian model to represent the statistics of atmospherically distorted wavefronts, limiting magnitudes up to ∼ +17 are predicted for an interferometer using two collectors each of 1 m 2 area. A restricted form of log-normal model is used to estimate the effects of scintillation on the pupil space interferometer.

Journal ArticleDOI
TL;DR: In this article, a two-state model (speech absent or speech present) is used in the derivation of a maximum likelihood estimator for the speech power, which is weighted by the a posteriori probability that the current measurement corresponds to the speech state.
Abstract: One way of enhancing speech in acoustic noise environments is to process the data using a noise suppression filter which performs a spectral decomposition of a frame of noisy speech and attenuates a particular spectral line depending upon how much the measured speech plus noise power exceeds an estimate of the background noise. In this paper a two‐state model (speech absent or speech present) is used in the derivation of a maximum likelihood estimator for the speech power. The result is a suppression curve that is similar to existing algorithms but which is weighted by the a posteriori probability that the current measurement corresponds to the speech state. A class of curves is obtained by varying the value of a suppression factor which can be chosen to trade off noise suppression against speech distortion. The algorithm has been implemented in real time in the time domain, exploiting the structure of the channel vocoder to perform the spectral decomposition. Extensive testing has shown that the noise ca...

Proceedings ArticleDOI
01 Jan 1979
TL;DR: In this article, the authors have designed and fabricated 32×32 charge injection devices (CIDs) on mercury cadmium telluride of approximately 5 µm cutoff wavelength to achieve high performance infrared system applications.
Abstract: Certain high performance infrared system applications can be met by x-y addressable area array sensors where the center-to-center spacing of the image resolution elements is small while at the same time the signal to noise ratio is high. We have designed and fabricated 32×32 charge injection devices (CIDs) on mercury cadmium telluride of approximately 5 µm cutoff wavelength to achieve these goals. The device design and fabrication are summarized, and the important observations of good charge transfer efficiency (>99.5%), high storage times in the MIS wells, and optical response uniformity are presented. Based on the present experimental data, 3-5 µm monolithic mercury cadmium telluride arrays are promising devices for staring IR imaging system.

Journal ArticleDOI
TL;DR: In this article, an algorithm for maximum posterior probability (MPP) demodulation of angle-modulated signals is presented, in which additive Gaussian noise and Gaussian modulating signal are assumed.
Abstract: An algorithm is presented for maximum posterior probability (MPP) demodulation of angle-modulated signals. A sampled data version of the problem is considered, in which additive Gaussian noise and Gaussian modulating signal are assumed. The algorithm is a numerical method for solving the nonlinear equations which are necessary conditions for MPP estimation. Results of a simulation of the algorithm are presented and discussed. Improvements in performance with respect to a phaselocked loop appear to stem from use of data before and after the time position of a phase estimate and from optimization of performance at low signal-to-noise ratio (SNR) as well as at high SNR.

Journal ArticleDOI
Irving Kanter1
TL;DR: In this article, an expression for the probability density function (pdf) of the monopulse ratio when skin echoes from a passive target are contaminated by interference from a jammer is presented.
Abstract: An expression is applied for the probability density function (pdf) of the monopulse ratio when skin echoes from a passive target are contaminated by interference from a jammer. The analysis is valid for arbitrary signal-to-jam ratio and arbitrary locations of the target and jammer in the beam. For an on-axis skin target and a stand-off jammer at an off-axis location, the "pulling" effect of the jammer and the accuracy of the angle estimate are compared with the approximations currently employed in radar performance analysis. The pdf of the monopulse ratio for large and for small signal-to-jam ratios is presented, showing that the pdf is bimodal at small signal-to-jam ratio.

Journal ArticleDOI
W. Aranguren1, R. Langseth
TL;DR: The method utilizes the fact that the desired signal has a nearly constant envelope; with interference present, the composite envelope becomes noisy, and a controlling processor measures this additional envelope noise, and iteratively adjusts the complex combining gain of an auxiliary signal to minimize the interference.
Abstract: We discuss a possible method for interference control in radio systems whose desired signal is analog FM. The method utilizes the fact that the desired signal has a nearly constant envelope; with interference present, the composite envelope becomes noisy. A controlling processor measures this additional envelope noise, and iteratively adjusts the complex combining gain of an auxiliary signal to minimize the interference. The expected residual interference remaining after minimization is proportional to the reciprocal of the square of the rms envelope fluctuation of the desired signal. This result was confirmed in a laboratory simulation of an intersecting radio route case using both large and small index FM. Beginning with signal-to-interference ratios of 30 to 40 dB, the controller increased these numbers to about 60 dB, the expected theoretical limit for a signal with 0.1 percent rms envelope fluctuation.

Proceedings ArticleDOI
01 Apr 1979
TL;DR: The superiority of SGEP over the stochastic approximation predictor is illustrated by waveforms and snr (signal to noise ratio) performance curves.
Abstract: A sequential gradient estimation predictor [SGEP] for speech signals is presented. In a given sampling interval, each prediction coefficient in turn is increased and decreased in value by a prescribed amount, while the other coefficients are kept constant. Two predictions are then made and the better enables the coefficient to be modified in the correct direction, but by an amount determined by a number of factors. The superiority of SGEP over the stochastic approximation predictor is illustrated by waveforms and snr (signal to noise ratio) performance curves.

Journal ArticleDOI
TL;DR: The ZAB-2F instrument manufactured by VG-Micromass Ltd is capable of measuring peaks corresponding to the arrival of ions at a rate of the order of 1 ion s−l.

Patent
25 Oct 1979
TL;DR: In this article, the amplitude of the signal in each path is compared with the noise in that path to produce a difference voltage for each path, the difference voltages from different paths are compared one with another and the path having the largest difference voltage is selected for transmitting the wanted signal.
Abstract: The evaluator allows route selection to occur both in terms of the path the communications travel to the central station and in terms of the signal-to-noise ratio of any path, i.e. the path with the largest signal to noise ratio is selected. The amplitude of the signal in each path is compared with the noise in that path to produce a difference voltage for each path. The difference voltages from different paths are compared one with another and the path having the largest difference voltage is selected for transmitting the wanted signal.

Proceedings ArticleDOI
Lloyd M. Logan1
29 Oct 1979
TL;DR: In this paper, the S/N capability of an Idealab Fourier Transform Spectrometer using a HgCdTe detector was improved by a factor of 30 to a level where system performance with a Nernst glower source was limited only by the extrinsic detector noise.
Abstract: The S/N capability of an Idealab Fourier Transform Spectrometer using a HgCdTe detector was improved by a factor of 30 to a level where system performance with a Nernst glower source was limited only by the extrinsic detector noise. The results reported here constitute a hardware demonstration of an analysis recently performed by Zachor and Aaronson. Our analysis and hardware demonstration are in substantial agreement with the work of Zachor and Aaronson which was carried out independently. Diagnostic data will be presented which illustrate the distortion to the spectrum caused by errors in sampling. The characteristics/specifications for signal and sampling control electronics which provide dynamic compensation for sampling errors will be discussed, and test data showing the 30 fold improvement in S/N will be presented.

ReportDOI
11 Jun 1979
TL;DR: In this article, the authors used the maximum likelihood technique to extract pitch for speech that has been corrupted by additive noise, using a comb filter bank estimator-correlator.
Abstract: : Using the maximum likelihood technique an algorithm is developed for the extraction of pitch for speech that has been corrupted by additive noise. The speech model includes the effects of pitch periodicity and the spectral envelope which results in a processing structure that consists of a noise suppression prefilter in cascade with a comb filter bank estimator-correlator. The prefilter attenuates those frequency bands where the speech signal-to-noise ratio is low, hence most of the deleterious noise is rejected prior to the determination of pitch by the comb filter bank correlator. The comb filter interpretation leads to an implementation of the correlation function which avoids the problem of anomalous pitch errors due to the effects of windowing and formant sidelobe interaction which obviates the need for any type of spectral flattening. Pitch ambiguities are resolved using a majority logic scoring algorithm and a carefully designed pitch tracker that can adapt rapidly to gross pitch variations. The voiced/unvoiced decision is based on an adaptive minimum energy threshold, a high/low band energy measurement, a normalized pitch correlation coefficient and a pitch track continuity coefficient. A time domain implementation of the algorithm that runs in real time in conjunction with an LPC analysis/synthesis system at 2400 bps is described. (Author)