Showing papers on "Signal-to-noise ratio published in 1978"

Adaptive noise canceling for speech signals

Abstract: A least mean-square (LMS) adaptive filtering approach has been formulated for removing the deleterious effects of additive noise on the speech signal. Unlike the classical LMS adaptive filtering scheme, the proposed method is designed to cancel out the clean speech signal. This method takes advantage of the quasi-periodic nature of the speech signal to form an estimate of the clean speech signal at time t from the value of the signal at time t minus the estimated pitch period. For additive white noise distortion, preliminary tests indicate that the method improves the perceived speech quality and increases the signal-to-noise ratio (SNR) by 7 dB in a 0 dB environment. The method has also been shown to partially remove the perceived granularity of CVSD coded speech signals and to lead to an improvement in the linear prediction analysis/synthesis of noisy speech.

The Choice of the Desired Impulse Response in Combined Linear-Viterbi Algorithm Equalizers

Abstract: Equalizer structures using the Viterbi Algorithm achieve at least order of magnitude performance improvement over linear equalizers on some intersymbol interference channels. Using a linear equalizer to shape the original channel impulse response to some shorter desired impulse response (DIR) is a technique which reduces the complexity of the Viterbi Algorithm equalizer. This paper looks at three techniques for choosing a DIR. These are choosing the DIR by truncation, minimum mean square error and matching the power spectrum to that of the original channel. Using effective signal to noise ratio as the figure of merit for comparison, results are given for one particular channel.

FIR system modeling and identification in the presence of noise and with band-limited inputs

Abstract: System identification, that is, the modeling and identification of a system from knowledge of its input and output signals, is a subject that is of considerable importance in many areas of signal and data processing. Because of the diversity of applications, a number of different methods for system identification with different advantages and disadvantages have been described and used in the literature. In this paper we investigate the performance of three well-known system identification methods based on an FIR (finite impulse response) model of the system. The methods will be referred to in this paper as the least squares analysis (LSA) method, the least mean squares adaptation algorithm (LMS), and the short-time spectral analysis (SSA) procedure. Our particular interest in this paper concerns the performance of these algorithms in the presence of high noise levels and in situations where the input signal may be band-limited. Both white and nonwhite random noise signals as well as speech signals are used as test signals to measure the performance of each of the system identification techniques as a function of the signal-to-noise ratio of the systems output. Quantitative results in terms of an accuracy measure of system identification are presented and a simple analytical model is used to explain the measured results.

First-order statistics of a non-Rayleigh fading signal and its detection

Abstract: The first-order statistics of the vecter sum of a complex Gaussian variable and N complex exponentials with constant amplitudes but random independent phases are used to model a non-Rayleigh fading signal. Envelope detection, optimal for detecting Rayleigh (N = 0) and Rician (N = 1) signals, is also shown to be optimal for the considered non-Rayleigh signals in additive white Gaussian noise. However, the signal-to-noise ratio required to detect the latter signal for N = 2 may be substantially higher than for the former cases. Possible applications of this fading model to studies of multipath fading, non-Rayleigh sea echoes, microwave or laser radar detection and tracking are discussed.

Signal-to-noise ratio in optical heterodyne detection for Gaussian fields

Abstract: The signal-to-noise ratio of optical heterodyne detection is discussed for Gaussian fields. The ratio of the aperture radius a of the detector to the smallest spot size w(s) of the signal has serious effects on the SNR. The conditions that maximize the SNR are obtained for a given signal or local oscillator field. The effects of field mismatching or misalignment are also discussed. Numerical analyses show that when such mismatching or misalignment exists, the spot size of the local oscillator field should be larger than that of the signal with a ratio of a/w(s) approximately 1.2. Then the heterodyne efficiency is rather insensitive to the errors and yet takes reasonable values (above 0.8).

Noise monitoring apparatus

Abstract: An apparatus for monitoring the noise which impinges a human ear and for generating a signal representing the noise level accumulated over a period of time. Typically, the apparatus can be located in a hearing protector worn by a worker in a noisy environment. A microphone generates a signal having a magnitude representing the detected noise level of the ear which signal is processed by an absolute value circuit and a root mean square circuit to generate a signal having a magnitude proportional to the logarithm of the detected noise level. This logarithmic signal is converted by a voltage to frequency converter and a counter accumulates a count total proportional to the noise level over a period of time. The apparatus includes visual and aural alarms to indicate a maximum allowed noise level and dosage. The apparatus can also be inserted into a storage unit for reading the data, calibrating the noise monitor circuitry and recharging the batteries in the apparatus.

Matched Filter Criteria and Range Weighting for Weather Radar

Abstract: The effective weighting function for weather radar is defined. This weighting function considers the effects of both the transmitted signal and the receiver filter. It is used to assign effective ranges to samples taken at prescribed times. For uniformly distributed targets it is shown that "signal"-to-noise ratio depends on the receiver filter, transmitted signal envelope, and receiver noise spectral density. Maximization of this signal-to-noise ratio when range resolution constraints are imposed is discussed, and a receiver design approach specifically adapted for Doppler weather radars is developed.

The PROM - A Status Report

Abstract: The PROM is a solid-state, rapidly recyclable, image storage device having a number of applications in image and signal processing. Some of its important characteristics include 1/10-wave optical surface quality, 100-1p/mm three-bar resolution, 10 ergs/cm2 light sensitivity, and image plane contrast of 10 4 :1. One of the unique features of the PROM is that the bias level of stored patterns can be adjusted through application of an external voltage, resulting in image contrast inversion or enhancement. This same operation (baseline subtraction) is used to null the zero order in an optical Fourier transform, achieving a Fourier plane signal-to-noise ratio approaching 106:1. This paper reports on the current status of this device and a number of applications for which it has been tested in several areas of image and signal processing. Results are shown for coherent optical processing by computer-controlled Fourier plane filtering and real-time image correlation, and signal processing systems are described which couple the PROM with an acousto-optic raster recorder to perform spectrum analysis and correlation on radio frequency signals.

Analysis of neuronal networks in the visual system of the cat using statistical signals -- Simple and complex cells

Abstract: Superimposing additively a two-dimensional noise process to deterministic input signals (bars) the neurons of area 17 show a class-specific reaction for the task of signal extraction. Moving both parts of the signals simultaneously and varying the signal to noise ratio (S/N) the simple cells achieve the same performance as resulted from the psychophysical experiment. Type I complex cells extract moving deterministic signals (i.e. bars) from the stationary noise, whereas in the answers of Type II complex cells the statistical parts of the signals predominate. Considering the different cell types each as a series of a linear and a nonlinear system one obtains the cell specific space-time frequency and the amplitude characteristics.

Wireless transmission system

Abstract: A wireless transmission system for substantially noise-free transmission including a portable, battery powered, self contained transmitter for transmitting signals representative of an audio input to a remote receiver The transmitter includes noise reduction encoding circuitry for processing a transduced audio input signal and providing a processed output signal to a transmission unit for transmission to the remote receiver The remote receiver receives the transmitted signals and supplies the received signals to a reception unit including noise reduction decoding circuitry for processing the received signal and providing an audio signal output with improved signal to noise ratio to a utilization device

Single-threshold detection of a random signal in noise with multiple independent observations. 1: Discrete case with application to optical communications.

Abstract: A single-threshold processor is derived for a wide class of classical binary decision problems involving the likelihood-ratio detection of a signal embedded in noise. The class of problems we consider encompasses the case of multiple independent (but not necessarily identically distributed) observations of a nonnegative (nonpositive) signal, embedded in additive, independent, and noninterfering noise, where the range of the signal and noise is discrete. We show that a comparison of the sum of the observations with a unique threshold comprises optimum processing, if a weak condition on the noise is satisfied, independent of the signal. Examples of noise densities that satisfy and violate our condition are presented. The results are applied to a generalized photocounting optical communication system, and it is shown that most components of the system can be incorporated into our model. The continuous case is treated elsewhere [ IEEE Trans. Inf. TheoryIT-25, (March, 1979)].

Low contrast measurement apparatus

Abstract: A low contrast measurement apparatus for electronically measuring video signal modulation under low contrast scene conditions. The measurement apparatus utilizes a low contrast periodic optical bar chart in conjunction with a filter-integrator processor to measure very low contrast ratios. The filter-integrator processor contains a filter which is tuned to the corresponding fundamental frequency of the bar chart, thereby reducing the noise bandwidth and consequently improving the signal-to-noise ratio. The filtered signal is integrated over one whole picture frame which results in an improved signal to noise ratio. The integrated output of the filtered video signal constitutes a linearly increasing ramp with a period equal to the frame time and whose height is proportional to the amplitude of the periodic signal.

Soft Decision Demodulation for PCM Encoded Speech Signals

Abstract: The effect of digital errors in PCM encoded speech signals transmitted over a noisy channel is reduced by using soft decision demodulation at the receiver. The reliability information supplied by the soft decision demodulator is used to point out likely transmission errors, especially in the most significant PCM bits. When a likely transmission error is identified, the corresponding PCM word is rejected by the receiver and replaced by a predictor estimate or an interpolation estimate if delayed decisions are used. We have analyzed soft decision demodulation schemes for standard PCM encoded speech signals transmitted over the Gaussian channel with coherent PSK (phase shift keying). A signal to noise ratio gain in E_{b}/N_{0} of the order of 1-2 dB is Obtained at low input signal levels. The gain depends on the performance of the predictor or, alternatively, the interpolator. No modifications of the transmitter are required to obtain this improvement. The suggested soft decision schemes are optional at the receiver. The comparisons are made with hard decision demodulation.

Magnetic recording medium

Abstract: PURPOSE:To enhance the sensitivity of a magnetic tape in all the audio frequencies, reduce the recording magnetic field, and yet improve the signal to noise ratio of the tape by coating two layers of alloy magnetic materials of different coercive force on a non-magnetic carrier.

Hard Limiting and Sequential Detection Applied to Loran-C

Abstract: The combination of an antenna, a 100 kHz bandpass filter, a hard limiter, and a sequential detector can supply highly accurate Loran-C data to a digital processor, even under low signal-to-noise-ratio conditions. For such a simple, low-cost receiver, calculations are given for the accuracy of the envelope and phase tracking of the Loran-C signal as a function of the signal-to-noise (Gaussian and atmospheric) ratio, averaging time, and radian speed of the observer with respect to the transmitter. Mentioned are the quasi-noise censoring effects of the hard limiter. Besides the Loran-C application, the hard limiter-sequential detector system can in general be applied for low-cost, synchronous signal detection under poor signal-to-noise ratio.

Signal-to-noise ratio measurement of intermittent signals

Abstract: The signal-to-noise ratio of intermittent reception by a radio receiver from a push-to-talk transmitter is measured by comparing AGC voltage levels derived from a signal period with levels derived from the prior no-signal period containing noise only. The AGC voltages are applied to a pair of integrators having corresponding time constants and therefore normally having equal outputs. When a valid signal period is recognized, the output of one integrator is held to represent an integration of voltage levels during the prior no-signal period. The integrated signal thus held is thereafter compared with the running output of the other.

On the detection of target trajectories in a multi target environment

Abstract: The tracking and ultimate identification of closely spaced objects is an area of interest to many surveillance systems. Much effort in recent years has been concentrated on the more "front-end" problem of optimizing the initial detection. However, the sorting and processing of crossing tracks and parallel tracks is a problem regardless of signal to noise ratio. In this paper, the application of a pattern recognition approach is investigated. A simulated track scenario is developed and the approach evaluated using the scenario. Examples of performance and results of the simulation study are given.

Video signal communications system with improved signal-to-noise ratio

Abstract: A television communications system enhances the video signal-to-noise ratio by delaying video intelligence over an interval (as by loading the video into a store therefor), while obtaining a measure of its average value and dynamic range. At the transmitter, the video is then read out from memory, has its average value diluted and is amplified before transmission to approach the channel amplitude capacity. At the receiver, the communicated average value and dynamic range signals are utilized to restore the average value to the received wave--and to appropriately reduce its relative amplitude. The concomitant channel amplitude reduction, with offsetting amplitude enhancement at the transmitter, improves the composite channel transmission ratio.

Transverse 1/f noise in InSb thin films and the signal‐to‐noise ratio of related Hall elements

Abstract: Transverse 1/f noise in approximately 2‐μm‐thick InSb thin films is investigated experimentally at room temperature. Linear dependence of noise voltage on dc bias current is shown quantitatively. The noise intensity is inversely proportional to the number of conduction electrons in the bulk. The temperature rise of specimens due to Joule heating does not affect the noise intensity coefficient. The coefficient differs from sample to sample, which is reduced by the heat treatment of specimens, but is independent of the doped impurity concentration. As a result, the signal‐to‐noise ratio of related Hall elements is formulated for the first time for audio magnetic heads applications. The signal‐to‐noise ratio is nearly 80 dB for a 10‐G magnetic field in the audio frequency range.

LMS Adaptive filtering for enhancing the quality of noisy speech

Abstract: A linear mean square (LMS) adaptive filtering approach has been formulated for removing the deleterious effects of additive noise on the speech signal; Unlike the classical LMS adaptive filtering scheme, the proposed method is designed to cancel out the clean true speech signal. This method takes advantage of the quasi-periodic nature of the speech signal to form an estimate of the clean speech signal at time t from the value of the signal at time t minus the estimated pitch period. For additive white noise distortion, preliminary tests indicate that the method improves the perceived speech quality and increases the signal to noise ratio (SNR) by 7 db in a 0 db environment. The method has also been preliminarily shown to remove the perceived granularity of CVSD coded speech signals and to lead to an improvement in the linear prediction analysis/synthesis of noisy speech.

Methods and apparatus for measuring signal-to-noise ratio

Abstract: Methods and apparatus are disclosed for measuring signal-to-noise ratio in video waveforms based on a novel application of the tangential noise measurement principle A calibrated video staircase test waveform is generated at the transmit end which permits a direct noise reading in dB at the measurement location by use only of a general purpose oscilloscope and associated band limiting and weighting filters The measurement is fast, straightforward and objective in nature

Image analysis nonlinear adaptive filter for improving signal-to-noise ratio

Abstract: A nonlinear adaptive filter for improving the signal-to-noise ratio of video signals generated from images of features under analysis typically includes filtering components for attenuating low amplitude video noise excursions while passing high amplitude video signal excursions substantially without attenuation. Attenuation of the noise is provided by electrical circuitry operating as a function of the voltage input. In general, the electrical circuitry has a predetermined relationship to the value of the video signal and its noise characteristic.

Procedures for analyzing interference caused by spread-spectrum signals

Abstract: : A mathematical procedure is given for determining whether a spread-spectrum signal will cause an unacceptable interference condition in a victim receiver. The procedure involves calculating either the interference-to-noise ratio or the signal-to-interference ratio at the IF-amplifier output and comparing the ratio with an appropriate threshold value. The front end and IF amplifier of the victim receiver are treated as a bandpass filter and non linear processes are not considered. (Author)

Delta modulated digital signal detector

Abstract: A detector for delta modulated digital signals is disclosed that provides a signal quality voltage having a magnitude that is indicative of the degree of quality of the detected delta modulated digital signal. The detector totalizes the number of bit transitions occurring in successive N bit intervals. If successive totalized numbers of bit transitions are outside of a predetermined range centered about one-half of N, the detector provides a detect indication signal indicating that the delta modulated digital signal is present. Otherwise, a random or pseudorandom signal such as noise or error bursts may be present. Digital circuitry provides the detect indication signal with a logical high state when successive totalized numbers of bit transitions are outside of the predetermined range, and a logical low state when succesive totalized numbers of bit transitions are within the predetermined range. The detect indication signal may be further integrated and amplified to provide a signal quality voltage which has a magnitude indicative of the quality or signal to noise ratio of the detected delta modulated digital signal. The signal quality voltage may be advantageously utilized in a receiver voting system having a plurality of receivers for selecting the receiver having the highest quality signal.

A simple method for the direct comparison of acoustic emission detection systems

Abstract: Inability to determine the absolute sensitivity of acoustic emission transducing systems has long presented a problem for workers in this field. A simple, low cost method is described for the measurement of absolute signal to noise ratio in response to white noise excitation energy as produced by a jet of helium gas. This method facilitates the direct comparison of system sensitivity, in the range 0–1.0 MHz, regardless of the type of signal conditioning used.

The influence of background noise level and signal duration on the judged annoyance of aircraft noise

Abstract: A series of 72 flyover events were assessed by a jury of 35 observers, during 12 separate listening sessions conducted in a controlled test area designed to simulate typical indoor listening conditions Each aircraft signal was superimposed on a controlled random traffic background signal having a duration exceeding that of the aircraft event The presence of a steady mean traffic background noise can reduce the perceived noisiness of aircraft flyover events, provided that the judgment time available is sufficiently greater than the event time (time in excess of background) For a given peak event level, a reduction in associated background noise of 21 dBA is shown to be equivalent subjectively to an increase of 55 dBA in peak event level, with fixed background conditions Although regressions obtained with the noise pollution index, L sub NP, for single event judgments generally showed a lower correlation than the L sub o and L sub p - L sub o regression variables, the score data did show a number of significant trends which are also associated with the LNP index variations computed for single noise events

Detection of a Coherent Quantum Signal in Thermal Noise

Abstract: : Methods are presented for calculating the minimum attainable probability of error in detecting a coherent quantum signal received amid thermal noise in the limits of low and high signal-to-noise ratio. In the latter limit, quantum-mechanical perturbation theory is applied to solving the detection operator equation approximately. Graphic results are furnished for binary signals transmitted with equal prior probabilities. Previous work on this problem is thus extended to a broader range of signal and noise strengths. The results are applied to the detection of antipodal two-photon-coherent-state signals. (Author)

Automatic Detection, Timing and Preliminary Discrimination of Seismic Signals with the Instantaneous Amplitude, Phase and Frequency

Abstract: : The feasibility is evaluated of applying instantaneous amplitude, phase and frequency measurements to automatically detect, time and identify seismic events. Detection based on phase measurements is shown to be in principle 6 dB more sensitive than detection based on amplitude measurements. A phase detection and timing algorithm, using a priori known dispersion characteristics, is demonstrated to time the onset of simulated teleseismic long-period surface waves within 30 seconds accuracy in 70% of the tested cases, for waveforms down to 0 dB signal-to-noise ratio. By phase measurement, rather than by amplitude measurement, this algorithm also provides a measure of the surface wave signal-to-noise ratio. These results can be applied in the extraction of weak surface waves. Phase detection of teleseismic short-period bodywaves was not found to be feasible, due to the interference of early- arriving secondary signals. Therefore, short-period P-wave detection and timing are performed essentially by envelope peak detection; instantaneous frequency measurements are also used in the timing process. Measurements of the instantaneous frequency permit analysis of the delay times of secondary signals partially overlapping with earlier primary signals, down to the primary signal detection level.