Showing papers on "Impulse noise published in 1981"

Influence of vibration on asymptotic threshold shift produced by impulse noise.

Abstract: Monaural chinchillas were exposed for 10 days to one of these conditions: (1) whole-body vibration (30 Hz, 1 g rms acceleration); (2) impact noise (113 dB peak SPL 1/s) or (3) a combination of whole-body vibration and impact noise. Thresholds were monitored before, during and after the exposure using the auditory-evoked response or behavioral conditioning techniques. Vibration alone had essentially no effect on threshold. Exposure to impact noise produced a stable asymptotic level of threshold shift 2-8 h after exposure onset. The asymptotic threshold shift was roughly 35 and 43 dB SPL at 0.5 and 8.0 kHz, respectively. Exposure to impact noise plus vibration produced an asymptotic threshold shift at 0.5 and 8.0 kHz that was approximately 10 dB greater than noise alone. The combination group also showed greater permanent threshold shifts and greater hair cell losses than the group exposed only to impact noise. The results imply that impact noise and whole-body vibration, at levels commonly found in industr...

Impulse noise reduction system for TV receivers

Abstract: A television receiver having circuitry for reducing the effects of impulse noise in the video signal is controlled by impulse noise detection circuitry responsive to the accompanying sound signal. Since impulse noise is relatively broadband it will occur simultaneously in both the broadcast picture and accompanying sound signals. Amplitude variations of the frequency modulated sound signal are indicative of the presence of noise, which variations are detected and utilized to generate a control signal whenever the noise amplitude exceeds a predetermined threshold.

Variable peaking control circuit

Abstract: A video signal processing circuit including signal substitution circuitry for eliminating impulse noise has a signal peaking circuit conditionally operable for the duration of one or more video fields depending upon the presence of noise being detected in the vertical blanking interval. A circuit responsive to enabling pulses generated as a result of impulse noise or defects being detected in a vertical blanking interval provides one of two peaking control signals for controlling the level of peaking applied to the video signal by the peaking circuit.

Noise processing system for a television receiver

Abstract: A noise processing system is described for use in protecting a television receiver's sync processing path and its video processing path from impulse noise. To protect the video processing path, a first noise canceller receives a composite video signal, detects each noise pulse therein which exceeds a video noise threshold, and replaces each such noise pulse with a selected voltage level. The resultant noise processed video may then be applied to the receiver's video processing path. To protect the sync processing path, another noise canceller receives the composite video signal, detects noise pulses therein which exceed a sync noise threshold, generates a detection pulse for each such noise pulse, and combines the detection pulses with composite video so as to cancel the noise pulses. Thus, another noise processed video signal is developed for application to the receiver's sync processing path.

Digital FSK receiver capable of operating in high impulse noise environments

Abstract: The Advanced Group Rapid Transit (AGRT) FSK communication link is required to operate with a bit error rate of 10-5errors/bit. Inductive coupling between a wire loop embedded in the guideway and a rectangular coil antenna mounted beneath the vehicle provide the medium of communication. Susceptibility of such loops and antennas to noise has been a problem in the design of a reliable communication link. Past data taken on the Morgantown People Mover System and the Seattle Metro Trolley installation show that sinusoidal interference and Gaussian noise were negligible, but low PRF impulse noise from 1) the chopper controlled propulsion unit on board the vehicle and 2) the contact bounce of the power collectors is very severe. Cases were even observed where the signal to noise ratio within our FSK passband (100 - 150 KHz) fell as low as 0 dB. Due to the importance of meeting the bit error rate requirement even in such an environment, much time was spent in the development of a suitable receiver. The digital demodulation technique which detects frequency by digitally measuring the period (1/f) of the received signal was one of the concepts considered. The development of the Digital FSK Receiver using this technique is the topic of this paper. Initial development of this receiver was performed with a TTL logic implementation of the demodulator. The TTL logic implementation was then tested in severe impulse noise environments in order to evaluate the feasibility of this concept. The successful performance of this implementation prompted a Z8 microcomputer based design. The implementation of both receivers will be discussed along with the tests and test results obtained.

Potential for Interaction of Low-Level Impulse and Continuous Noise

Abstract: : The purpose of the experiments described in this report was to establish whether a synergistic interaction occurs between relatively low levels of continuous and impulse noise to produce an increased hearing loss and cochlear pathology. Twenty-three monaural chinchillas were used as experimental subjects. The animals were divided into six groups. Each group was exposed 8 hours per day for 8 weeks to various combinations of impulse and continouous noise presented at various levels. Using behavioral conditioning techniques, hearing thresholds were measured before, during, and after noise exposure. After a minimum of 30 days post-exposure the animals were killed and their cochleas were analyzed using the surface preparation technique. Histological results were qualified in the form of a cochleagram. In contrast to earlier findings the results of this study found no evidence of a synergistic interaction when the animals were exposed to a combination of continuous (between 75-85 dB SPL) and impulse (103 dB SPL peak exposure) noise. (Author)

Adaptive algorithm for detection of signals in an impulsive interference environment

Abstract: Impulsive interferences are frequently long relative to signal duration. This situation is observed, for example, in a telephone channel used for medium and high-speed data communication. In this paper a novel algorithm for signal detection under conditions of long impulsive interferences is proposed. The approach does not require a priori knowledge of the impulse noise statistics. It is based on the representation of the impulse noise using a linear prediction model. Performance of I he proposed algorithm is investigated using computer simulation. It is shown that the algorithm provides a greatly reduced error rate as compared with the conventional non-linear receiver. Its performance is virtually independent of the power of impulse noise.

Locating noise in communications systems

Abstract: An impulse noise source in a bidirectional submerged communications system is positionally located by detection apparatus at one end of the system which measures the time interval between the same impulse arriving twice at the one end of the system, firstly, via a shorter or faster path in the system (either the incoming path to the one end, or a reference frequency band in the incoming path) and, secondly, via a longer or slower path in the system (either the go path from the noise source, a go/return distant loop and the incoming path, or another frequency band in the incoming path). Group delay distortion of the system affects the location accuracy and is equalized by networks in the detection apparatus.

Community Reaction to Impulse Noise: Initial Army Survey.

Abstract: : This report gives the results of a noise-impact attitudinal survey done in the Fort Bragg/Fayetteville, NC, area. It shows that to the extent normal sources like airplanes fit an energy model (such as the day/night average sound level (DNL), impulse noise also fits an energy model. The growth of annoyance levels in a community with increases of loudness occurs similarly for impulse noise and for aircraft and helicopters. The growth of annoyance in a community with increases in the frequency of occurrence of events occurs in a similar way for all noises, except that the integration period for impulse noise apparently extends down to 'once every few months,' whereas annoyance all but dies away for other noises when the frequency of occurrence drops this low. All types of noise sources have roughly the same nighttime noise penalty -- 7 to 10 dB. C-weighting is the best available standard measure; a C-weighted DNL (CDNL) which includes no threshold or impulse correction factor offers the best model to describe community response. To establish an equivalency between CDNL levels used to assess impulse noise and A-weighted DNL (ADNL) levels used to assess other noise, it is necessary to find a common denominator. It is recommended that the percent of the community 'highly annoyed' in a given noise climate be that common denominator. With this common denominator, about 6 dB must be added to the numerical value of the CDNL level. (Author)

Änderung des Spitzendrucks und der Frequenz des Impulsschalls vom Freifeld zum Ohr in seiner Bedeutung für das akustische Trauma des Ohres

Abstract: In case of impulse noise peak level is enlarged about 5–10 dB in the auditory meatus. The spectrum of the noise is changed in direction of higher frequencies. This is essential for damage risk criteria of impulse noise and judgement of protectors. The resonance of the meatal cavity should be considered for explanation of high tone loss through impulse noise of high energy.

Smoothing of Impulse Noise by Orthogonal Transform

Abstract: Electromagnetic impulse noise which is harmful to signal measurement or transmission of information, is smoothed by the orthogonal transform processor. The idealized impulse noise with infinitesimal duration and Gaussianly-distributed amplitude shows the same spectral characteristics as white Gaussian noise. Optimal correlation detector against such noise is easily realized by the orthogonal transform processor. Photoelectric pulse signals disturbed by the impulse noise from the power supply can be well detected through the Walsh waveform analyzer. Also, orthogonally-synthesized signals can be demodulated with firmly-suppressed impulse noise, where both the statistical and instantaneous SNRs are superior to those in the usual PCM transmission system.

Asymptotic Performance of Nonlinear Demodulators in Impulsive Noise

Abstract: We present a technique for calculating the bit error rate performance of nonlinear demodulators operating in impulsive noise in the limit of large time-bandwidth products. The asymptotic limit is given, together with first- and second-order corrections. We calculate bit error rates with two nonlinearities, a bandpass limiter and a low-pass limiter; the two are found to give very similar results. The computational technique is applicable to all noise distributions. We present results for two distributions, an analytic continuation of the Hall model and a truncated Hall mode. The models yield significantly different results.

The Temporary Threshold Shift and Its Relation to Permanent Inner Ear Damage Following Exposure to Impulse Noise

Abstract: It is widely accepted that for continuous noise, a relationship exists between the energy of sound (A-weighted) and its deleterious effects on hearing. However, when the exposure is to noise which contains high intensity short duration impacts or impulses, a hitherto unpredictable degree of damage can occur to the inner ear.

Änderung des Spitzendrucks und der Frequenz des Impulsschalls vom Freifeld zum Ohr in seiner Bedeutung für das akustische Trauma des Ohres

Abstract: In case of impulse noise peak level is enlarged about 5–10 dB in the auditory meatus. The spectrum of the noise is changed in direction of higher frequencies. This is essential for damage risk criteria of impulse noise and judgement of protectors. The resonance of the meatal cavity should be considered for explanation of high tone loss through impulse noise of high energy.