Showing papers on "Background noise published in 1971"

Preferred noise criterion (PNC) curves and their application to rooms.

Abstract: The noise criterion (NC) curves were developed both as a method for evaluating existing noise situations and as a means for specifying design goals for noise control. They have also influenced the N ratings used abroad. It has been demonstrated that if a background noise whose spectrum conforms to an NC‐curve shape is deliberately generated, it does not sound to a listener as a pleasant or neutral noise, but is both “hissy” and “rumbly.” A recent tendency in consulting practice, therefore, has been to specify noise levels that are lower than NC curves at both low and high frequencies. Also, the original NC curves were derived using Stevens's Mk. I method of calculating loudness level from noise levels measured with the old octave bands, the lowest of which was the “below 75 Hz” band. A reexamination of the noise criterion curves has been undertaken using Stevens's Mk. VI method and the new octave bands. The result is a new set of curves, called “preferred noise criterion (PNC) curves,” having levels in the bands below 125 Hz and above 1000 Hz that are lower than those of the 1957 NC curves by 2–5 dB. The new set also takes into account the engineering realities of achieving the specified noise levels with conventional air‐handling equipment. The results of a number of recent noise‐control projects in building are presented for comparison.

Detection of a Distributed Target

Abstract: The influence of increasing range resolution on the detectability of targets with dimensions greater than the resolution cell is studied. An N-cell target model is assumed, which contains k reflecting cells, each reflecting independently according to the same Rayleigh amplitude distribution. It will be referred to as the (N,k) target. Detection based on one transmitted pulse is performed against a background of white normal noise. Detection in stationary clutter is also considered. The optimum detector is obtained but, in view of its complexity, the performance of a simpler detector, the square-law envelope detector with linear integrator (SLEDLI), is analyzed, and a formula for the probability of detection is obtained. Graphs are presented which show the probability of detection as a function of signal-to-noise ratio (SNR) for various values of N k, and false alarm probability. For N/k not too large it is shown that the SLEDLI is near optimum.

Nonparametric Radar Extraction Using a Generalized Sign Test

Abstract: A nonparametric procedure used in a constant false alarm rate (CFAR) radar extractor for detecting targets in a background of noise with unknown statistical properties is described. The detector is based on a generalization of the well-known two-sample sign test and thus requires a set of reference noise observations in addition to the set of observations being tested for signal presence. The detection performance against Gaussian noise is determined for a finite number of observations and asymptotically, for both nonfluctuating and pulse-to-pulse Rayleigh fluctuating target statistics. It is noted that the performance loss, as compared to the optimum parametric detector, depends critically on the number of reference noise observations available when the number of hits per target is not large. In the same case a much larger loss is also found for a pulse-to-pulse fluctuating target even though the asymptotic loss is the same as for a nonfluctuating target. A comparison is finally made with a detector based on the Mann-Whitney test, which usually is considered to be one of the better nonparametric procedures for the two-sample case.

Field measurement of infrasonic noise

Abstract: Portable equipment for the detection and recording of noise in the frequency range from 2 to 500 Hz is described, together with typical results obtained in an automobile, blast furnace, railroad car, engine room, and helicopters. Factors responsible for peaks appearing at various frequencies are identified, and research on the subjective effects of infrasonic noise is indicated.

Radio Noise Design Guide for High-Voltage Transmission Lines

Abstract: Radio, television, and audio interference are rapidly becoming controlling factors in the design and planning of power lines. With the increasing attention being directed to the problem of the deterioration of man's environment, this subject will be given greater consideration by utilities in the future. This paper, sponsored by the Radio Noise Subcommittee, summarizes the state of the art at this date. Utility engineers and the industry should find it a valuable tool in the design of high-voltage transmission lines.

Circuit arrangement for attenuating a broadband background noise level and interfering signals superimposed thereupon

Abstract: A circuit for attenuating broadband background noise signals and narrower band interfering signals for facilitating detection of simultaneously appearing useful signals having a shorter duration than the interfering signals, the circuit including two channels for respectively attenuating signals in the narrower band and outside the narrower band but with a broader band, with an operational amplifier connected in at least one channel and controlled to have a constant output with respect to signals of longer duration than the useful signals, the amplifier output providing the desired circuit output signal.

Method and apparatus for the detection and recordation of high frequency sound in the cardiovascular system

Abstract: High frequency sound, such as that produced by turbulence, in the cardiovascular system is sensed, amplified, demodulated, and filtered to produce an average of the amplitude of the sound, the demodulated signal being synchronously averaged over a plurality of successive cycles of the heart to produce a clear signature trace of the demodulated sound, even in the presence of background noise.

Directional audiometry. II. The influence of azimuth on the perception of speech.

Abstract: In 30 persons with normal hearing, a previously described apparatus (Tonning, 1970) was used for free field determinations of the intelligibility of speech in relation to the azimuth of the source: Directional Threshold of Intelligibility (DTI) was recorded both with and without background noise. Two loudspeakers, the one producing speech and the other producing white noise, could be rotated independently in the horizontal plane around the test person, permitting an analysis of the dependency of the DTI upon the positions of the speech and the noise source. The assumption is made that DTI is dependant on age. With the help of electronic computer analysis the material collected during the examinations was used to construct a standard diagram showing the DTI values in persons with normal hearing, with and without background noise.

An evaluation of methods for scaling aircraft noise perception

Abstract: One hundred and twenty recorded sounds, including jets, turboprops, piston engined aircraft and helicopters were rated by a panel of subjects in a paired comparison test. The results were analyzed to evaluate a number of noise rating procedures in terms of their ability to accurately estimate both relative and absolute perceived noise levels. It was found that the complex procedures developed by Stevens, Zwicker and Kryter are superior to other scales. The main advantage of these methods over the more convenient weighted sound pressure level scales lies in their ability to cope with signals over a wide range of bandwidth. However, Stevens' loudness level scale and the perceived noise level scale both overestimate the growth of perceived level with intensity because of an apparent deficiency in the band level summation rule. A simple correction is proposed which will enable these scales to properly account for the experimental observations.

Directional audiometry. 3. The influence of azimuth on the perception of speech in patients with monaural hearing loss.

Abstract: The Directional Threshold of Intelligibility (DTI) both with and without background noise has been determined in 37 patients with one-sided hearing defects ranging from a 30 dB loss to total deafness. Free field speech audiometry was done with an apparatus permitting independent radial positioning of a speech loudspeaker and a noise loudspeaker on the circumference of a horizontal circle centred on the head of the seated person examined. The DTI measured without noise not only depended upon the amount of the hearing loss in the defective ear, but also upon slight variations in the hearing ability of the good ear. A relationship between the DTI without noise and the normal ear's Pure Tone Average (PTA) in the range 500, 1 000, and 2 000 Hz was found. In the persons examined it was also found that when speech was reproduced against background noise under certain conditions the bad ear contributed to the perception oE speech if the person tested had one-sided PTA of 53 dB hearing level or less.

Combined beam forming and cross correlation of broadband signals from a multidimensional array using coherent optics.

Abstract: A coherent optical system design is proposed for simultaneously heterodyning, correlating, and beam forming on a large number of input channels. Techniques are described with application to two- as well as one-dimensional arrays. To accommodate the former, one direction in the optical aperture must serve both as a time and space dimension. The particular technique proposed resolves the apparent ambiguity. The method uses the phase of the correlation amplitude, after heterodyning, to effect the beam forming operation. Although the full theoretical correlation processing gain against background noise is not realized, very substantial gains and fine time and angle resolutions can be achieved. Because of its inherent physical simplicity, particularly as contrasted with electronic methods of similar capacity, the coherent optical correlator–beam former has significant advantages for many applications.

BIAS‐DEPENDENT STRUCTURE IN EXCESS NOISE IN GaAs SCHOTTKY TUNNEL JUNCTIONS

Abstract: Large‐amplitude excess noise has been observed in the tunneling current of degenerate p‐type GaAs–Au Schottky junctions. At 4.2 K the noise voltage exhibits well‐defined peaks as a function of bias voltage. The background noise exhibits a 1/f‐type spectral response, but the spectral response of some of the peaks indicates that tunneling via surface states with a single average lifetime occurs. Peaks in the noise voltage correspond in bias voltage position with structure in d2I/dV2.

Surface Wave Detection with a Broad Band Accelerometer

Abstract: WE report preliminary results of a study to determine the capability of a broad band vertical accelerometer to detect surface waves from small earthquakes. The instrument uses a quartz fibre in torsion and capacitive position sensing1. It was designed as a low noise, low drift broad band accelerometer and has produced data on Earth normal mode excitation after earthquakes (5 to 40 cycle h−1, ref. 2). For this study, the output was modified by an active filter to copy the response of Pomeroy et al.3 and Molnar et al.4. Such a response does not use the wide band aspects of this instrument and the shape was dictated primarily by the shape of the ground noise spectrum, which has a minimum in amplitude between periods of 20 and 30 s. This minimum may be inferred from the known decrease in noise amplitude with increasing period at shorter periods and seismic background noise data5. It is also shown in the data of Savino et al.6.

Speech Intelligibility in a Background Noise and Noise-Induced Hearing Loss

Abstract: A significant improvement in speech intelligibility in a background noise was shown in a group of industrial subjects conditioned to working in noise compared with a control group of university staff. Progressive deterioration of speech intelligibility in noise was found with noise-induced hearing loss after losses had occurred at the 2 kHz pure-tone audiometric frequency.

Experimental atmospheric absorption values from aircraft flyover noise signals

Abstract: Analysis of aircraft noise recordings to determine experimental values of atmospheric sound absorption

Optical filter analysis as a function of nonoptimum noise conditions.

Abstract: An experimental study was conducted to determine the effects of nonoptimum noise conditions upon the SNR of optical spatial filters. The experiments were performed utilizing matched and inverse filters that are generally recognized as the best types of filters for pattern recognition. Their signal-to-noise ratios were compared as a function of varying background noise. The results indicate that (1) the SNR is a decreasing function of increasing background noise size, and (2) the performance difference between the inverse and matched filters increases as the noise size decreases.

Zero-point fluctuations and thermal-noise standards

Abstract: It is concluded that the expression for the available noise power should include only the `thermal-noise? term, the `quantum-noise? term being associated with the detector or receiver. Statements of the relationship found in the literature require such a convention to permit unequivocal application of microwave-network analysis to noise-measurement problems.

Infrared Systems: I. Expressions for Signal and Background Induced Noise with Space Filters

Abstract: The purpose of this paper is to investigate the signal from an IR detector in a system employing a moving space filter. The space filter may be a reticle or simply a "flying spot" aperture. When the IR detector output is caused by background radiation, the Wiener spectrum description is presumed adequate. The linear scanning case is considered in greater detail. A calculation of the detector output spectrum is made, assuming a generally accepted Wiener spectrum and a scanning rectangular aperture.

Infrared Systems: I. Accuracy of Angle Measurement

Abstract: In this paper expressions are derived for the error in position measurement for the problem of estimating the position of an infrared target in a random background and the combined prob lem when white detector noise is also affecting the estimation. Space filters performing linear scanning, nutation, and rotation are considered. A linear scanning infrared system is then considered in greater detail. The noise on the error signal is calculated, taking into account both the estimation error, as discussed in the first part, and "false alarms" occurring in the scan area far from the target.

Signal enhancement system

Abstract: A signal enhancement method and apparatus including a computer arranged to process underwater signals at discrete spectral intervals for facilitating spectral signature recognition of submarines. An average of the spectral intensities of broadband noise on either side of the discrete spectral interval is computed and then subtracted from the spectral intensities of the specific narrow-band frequencies generated by the submarine, thereby eliminating any false combinations of nonrandom sidebands with random background noise. The remainder is then integrated with time producing a continuously increasing cumulative energy level of the discrete spectral interval when the energy thereof is originating from the submarine.

Evaluation of measures of aircraft noise

Abstract: Development of noise measurement units for airport and aircraft noise reduction and psychoacoustic studies

Sonar Doppler Discrimination In High Noise Environments.

Abstract: : The experiment was concerned with the ability of anti-submarine warfare helicopter-borne sonarmen to perform doppler discrimination in the high background noise existing aboard rotary winged aircraft. Performance on a frequency discrimination task was measured under conditions in which the background noise was varied in intensity up to levels approaching those found aboard helicopters. The level of the signal was also varied such that under some conditions the signal was only slightly audible above the noise while under some conditions the signals were clearly audible. It was found that the intensity of the noise was not, of itself, related to the acuity of frequency discrimination. Rather, the differences between the signal level and noise level was most directly related to pitch discrimination performance. It was concluded that, if the signal level could be maintained well above the background noise level, doppler discrimination would not be seriously impaired.

The Application of Information Feedback to an Amplitude-Modulated Laser Communications System

Abstract: The application of information feedback to amplitudemodulated (AM) laser communication systems used to transmit the value, of a continuous parameter is considered. The laser system is assumed to be quantum-noise limited. The particular information feedback technique used is here termed feedback averaging. It is found that the use of this technique improves the accuracy of the estimate of the parameter at the receiver over a corresponding one-way system. The effect of a multiplicative error (slow fading for example), background shot noise, and the fluctuation in the photon arrivals at the receiver due to the laser itself are considered. Both experimental and simulation results bear out the analysis. A Chebyshev bound for the probability of error is derived for the special case of an M -ary AM system, both with and without feedback.

The Intelligibility of Helium‐Speech as a Function of Speech‐to‐Noise Ratio

Abstract: : Three experiments compared the intelligibilities of helium-speech and normal speech masked by loud noise. Recordings were made of 5 talkers reading intelligibility word lists. Several panels of listeners heard these recordings masked by different levels of background noise. In Experiment 1, a fatigue effect seemed at first to be present differentially for the helium-speech, suggesting that short-term auditory fatigue may occur with helium. However, Experiment 2, designed to observe the effect on intelligibility of time during listening session that material was heard, refuted the notion of short-term fatigue effects. Experiment 3 incorporated results of the first two experiments to evaluate the effect of introducing varied levels of noise upon intelligibility of helium-speech and normal speech when order of presentation of gas mix was minimized.

Noise as Perceived by the Community

Abstract: Community aircraft noise intensity indexes from annoyance and physiological reaction standpoint, discussing sleep interruption, hearing loss, communication interference, etc