Showing papers on "Impulse noise published in 1984"

Noise‐induced hearing loss as influenced by other agents and by some physical characteristics of the individual

Abstract: The interaction of noise with a variety of other agents and with some physical characteristics of the individual to produce noise-induced hearing loss is reviewed critically. The review is restricted, for the most part, to publications since 1970. Other agents interacting with steady-state noise that are reviewed here include: (1) ototoxic drugs (kanamycin, neomycin, ethacrynic acid, furosemide, and salicylates), (2) impulse noise, and (3) whole-body vibration. Physical characteristics of the individual that are reviewed are: (1) age, (2) presence of previous hearing loss from prior noise exposure, (3) eye color, and (4) race. Suggestions for future research in this general area are also made. Some of these suggestions are as follows: (1) to extend studies of the interaction of steady-state noise with impulse noise, salicylates, and whole-body vibration to encompass a broader range of exposure conditions, including exposure conditions typically encountered by the worker, (2) to develop an animal model of presbycusis to explore the interactions of noise-induced hearing loss and presbycusis, and (3) to explore the potential interactions resulting from concurrent exposure to multiple agents, such as impulse noise and ototoxic drugs, in younger, more susceptible animals.

Effects of impulse noise and continuous steady state noise on hearing.

Abstract: In this study the effects on hearing induced by occupational exposure to impulse noise were compared with those induced by exposure to continuous steady state noise. Three groups exposed to impulse noise, one group exposed to continuous steady state noise, and an unexposed control group were studied. The hearing thresholds of the groups were measured by a puretone audiometer three times in two workdays. None of the groups showed significant differences between the hearing thresholds measured in the morning, at midday, and in the afternoon. Group 1 with the shortest duration of exposure and group 2 with the intermediate duration of exposure to impulse noise had the highest thresholds at 6000 Hz in both ears. Group 3 with the longest duration of exposure to impulse noise had the highest thresholds asymmetrically, at 4000 Hz in the left ear and at 6000 Hz in the right ear. The group exposed to continuous steady state noise also had the highest thresholds asymmetrically, in the left ear at 6000 Hz. It was concluded that the longer the duration of exposure to impulse noise the wider the region of the frequencies that showed raised threshold shifts in both ears. Impulse noise seemed to produce permanent threshold shifts at 4000 and 6000 Hz after a shorter duration of exposure than continuous steady state noise.

Nearly Optimal Detection of Signals in Non-Gaussian Noise

Abstract: : This dissertation addresses the problem of finding nearly optimal detector structures for non-Gaussian noise environments. It is assumed that the noise statistics are unknown except for a very loose characterization. Under this condition, the goal is to study adaptive detector structures that are simple, yet capable of high levels of performance. Attention is focused on the discrete-time locally optimal detector for a constant signal in independent, identically distributed noise. A definition for non-Gaussian noise is given, several common univariate density models are exhibited, and some physical non- Gaussian noise data is discussed. Two approaches in designing adaptive detector nonlinearities are presented, where it is assumed that the noise statistics are approximately stationary. Both proposals utilized simple measurements of the noise behavior to adapt the detector, and in several examples the adaptive detectors are shown capable of attaining nearly optimal performance levels. A simulation is presented demonstrating their successful application.

Noise reduction for stereophonic FM signals by high-speed sampling and linear interpolation

Abstract: In a noise reduction circuit for reception of stereophonic FM signals in which the demodulated signal is chopped at twice the pilot frequency for separation between left- and right-channel signals, the demodulated signal is sampled by a first sample-and-hold circuit in response to the output of the noise detector to store that portion of the signal which appeared immediately prior to the occurrence of an impulse noise. The demodulated signal is also sampled by a second sample-and-hold circuit at a frequency twice the pilot frequency to eliminate a noise which might arise due to the chopping of the demodulated signal. A signal is derived from the outputs of the first and second sample-and-hold circuits that indicates the slope ratio of the demodulated signal at the moment that occurred immediately prior to the impulse noise. The slope ratio signal is applied to a linear integrator to generate a compensating voltage which is summed with the signal sampled by the first sample-and-hold circuit at the level which occurred immediately prior to the occurrence of the impulse noise.

Method of detecting and correcting impulse noise errors in log data

Abstract: Disclosed is a logging technique wherein measured parameters which are inherently weighted average measurement values are inverse filtered to improve the resolution of the measured values. Higher resolution values of log measurements are obtained from information contained in the measurements themselves, and the response function of a logging tool. Measurement errors due to impulsive noise are detected, located and corrected using innovation data contained in the log measurements.

Time spread transmission system using block conversion

Abstract: In the digital transmission of non-telephone signals, impulse noise interference, such as switching machine noise, interruptions, etc., become problematic and it has become necessary to suppress them. to suppress impulse noise interference efficiently, this paper presents a time spread transmission system, which transmits digital signals spread on the time axis through a block conversion, and discusses the system construction and the noise attenuation characteristic. First, the requirements for the time spread matrix in a general communication channel with impulse noises and random noises, such as thermal noise, crosstalk, etc., are described. It is clarified that for the matrix a cyclic orthogonal one is most suitable. For a single impulse noise interference, noise amplitude attenuation characteristics of the system are improved by 3 dB, compared with those of the conventional smearing-desmearing filter method. Finally, the bit error rate is estimated for burst noise interference channel on a statistical noise model and it is shown that the bit error rate reduction of two decimals is achieved for the case of transmission rate 64 Kb/s and spread time 8 ms.

[Permanent shift of auditory thresholds caused by continuous and impulse noise: comparative studies].

Abstract: The studies included two groups of workers, only men, of maximally similar structure of age and length of employment but different exposure conditions. 112 cotton weavers worked under continuous noise and 64 forgers under impulse noise. Noise measurements demonstrated that in both groups the equivalent levels were almost identical (101.8 dB-A in the weaving room and 100.4 dB-A at the forge). The permanent hearing threshold shift in both types of exposure was found to exhibit similar time course, developing within 10-15 years of exposure, then stabilizing, and reaching the asymptote within about 20 years. Despite the same dose of acoustic energy, the hearing impairment induced by impulse noise was greater and is characterized by the maximum loss at 6 kHz frequency, as opposed to the notch at 4 kHz typical of continuous noise.

FM demodulator circuit for reducing the noise level in the demodulation result

Abstract: In the conventional FM demodulators with ratio detector, signals which approximately reach or even exceed the amplitude of the useful signal are particularly intensively disturbing. This applies both to noise and common frequencies but especially to impulse noise from electrical appliances and car ignition sparks. Figure 1.1 shows the block diagram of the invention. The non-limited FM signal F1 is mixed to form the less modulated FM signal F20. It passes at least through a filter with narrow bandwidth and goes to the limiter as F21. The limited signal F22 is demodulated in an FM demodulator of any type. The result is NF1. An adapter with, for example, amplifier(s), low-pass filter and, if necessary, phase correction provides NF2, the useful signal and drive signal for the VCO. The frequency F3 of the latter is controlled in such a manner that the signal F20 is produced with F1. The phase comparator with a fixed frequency, shown in Figure 1.2, has been found to be a suitable FM demodulator. A further extension is possible by frequency doubling with the method shown in Figure 1.3. In this arrangement, signals with overmodulation with 180 degrees phase shifts are still evaluated. The achievable advantages are drawn for 1kHz in Figure 2.1 and for 15 kHz in Figure 2.2. The diagrams relate to whole modulation VHF broadcast standard. They show the function of the demodulated signal/noise ratio in dependence on the RF signal/noise ratio with impulse and noise interference. ... Original abstract incomplete.

Synoptic observations of the radio noise background in the frequency range 150-180 kHz to provide design data for the low frequency communications designer

Abstract: : Observations were made of the radio noise background in the frequency range 150-180 kHz to provide reference data for the design of the Ground Wave Emergency Network (GWEN) system. These observations were undertaken at Nanjemoy, Maryland, during early summer 1983, and included forty-one days of data recording. The noise environment was found to be dominated by impulsive thunderstorm noise. Preliminary data analysis is presented; the recorded data is available on magnetic tape for authorized users to use for system design purposes.

Effect of impulse noise on data transmission using FDPSK

Abstract: The receiver impulsive characteristic (RIC) for binary frequency differential phase-shift keying (FDPSK) is evaluated. Numerical results for the error rate of the receiver preceded by an RLC filter are given. The results are compared to those of the widely used TDPSK.