Showing papers on "Impulse noise published in 1983"

Method and apparatus for reducing the effects of impulse noise in Loran-C receivers

Abstract: The effects of impulse noise on the operation of a microprocessor-controlled Loran-C receiver are reduced by muting or attenuating the received signals in the front end of the receiver ahead of the receiver gain during a time period which preceeds the start time of the pulses being tracked. The attenuation is selectively removed after the start time of each pulse being tracked to permit the receiver to perform its time difference of pulse arrival measurements in the normal manner. The attenuation is also selectively removed during those time periods in which the receiver performs its envelope slope, skywave/groundwave and other such samplings. The attenuation is provided by a muting circuit which is controlled by a time gate signal that derives from the microprocessor of the receiver.

Noise blanking arrangement to minimize blanker splatter

Abstract: Method and apparatus are provided for impulse noise blanking in a radio receiver wherein blanking attenuators are provided in both the wideband, prefilter stage and narrowband, postfilter stage of the receiver so that the bandwidth and location in the receiver in which blanking is provided is optimized dependent upon signal conditions.

Apparatus for reproducing motion picture film photographic sound-tracks to correct reproduction errors and reduce noise

Abstract: Apparatus for reproducing motion picture photographic (optical) sound-tracks is disclosed in which significant information regarding track placement, slit illumination, azimuth and impulse noise is derived by dynamically processing and comparing the signals obtained by reading each half of a bilateral sound-track. In a further embodiment a pair of detector elements monitors the septum between two tracks in order to detect lateral film misalignment.

The Detection of Signals in Impulsive Noise.

Abstract: : This dissertation addresses the problem of detecting known, discrete-time signals in additive non-Gaussian noise. The case of statistically independent samples is emphasized. After a brief introduction to the detection problem, the characteristics and sources of impulsive noise are discussed. Several models for impulsive noise are then presented. The complexity of these models and the need for simple density functions to approximate the first order characteristics of impulsive noise justify consideration of three systems of densities. These three systems are: a generalized Gaussian noise, the Johnson S(u) System, and a mixture model. These are used throughout this dissertation to provide examples. In many detection problems it may only be possible to define a class of probability densities which contains the actual noise density. In such cases minimax detectors may be used to guarantee a lower bound on detector performance for the entire class. The minimax detector is the optimum detector for the worst case density. It is shown that the worst case density, in terms of minimizing the asymptotic probability of detecting a singal, is that density which minimizes Fisher's Information over the entire class. Several classes of densities are considered and conditions are established for the minimax detectors.

An Acoustical Assessment of the Impulse Noise of Grenade Simulators Exploding in Enclosures

Abstract: : An assessment was made of the impulse noise produced when exploding grenade simulators both outdoors and at various locations and distances in two different shaped rooms with and without furnishings. The peak pressure level of the grenade simulator when measured outdoor was 178 dB and its B-duration was 6 msec. The effect upon the impulse noise produced by a grenade simulator exploding at various locations with reference to the walls is described. The effect of furnishings is given and equations are provided for computing peak pressure level and B-duration. A program is provided for producing idealized pressure time histories of the impulse noise with explosive and transducer at various locations with reference to the walls. Proper instrumentation techniques are provided for measuring impulse noise in rooms. The potential hazard for personnel who might undergo a once in a lifetime exposure is estimated for different impulse noise levels of exploding grenade simulators inside rooms. Also, appropriate precautions for use in training, such as hearing protection, maximum number of exposures and maximum exposure level, are discussed. (Author)

Impulse noise removing device

Abstract: PURPOSE:To obtain a satisfactory noise removing effect by dividing an input signal into a low frequency component and a high frequency component and, at the arrival of a noise, by processing the former component by integrating interporation system and interrupting the later component. CONSTITUTION:An input signal is emphasized at its noise component by a preemphasis circuit 2 and delayed by a delay time T1 exceeding noise time width in a delay circuit 3. An output of the circuit 3 is separated by an LPF4 and an HPF5 and the separated outputs are inputted to delay circuits 9, 13 respectively to make the signals delay by time T2. An output of the circuit 3 is also inputted to a control circuit 8 after removing its noise by a BPF6 and a noise detecting circuit 7. The input and output signals of the circuit 9 are subtracted by a subtractor 10 to find the level difference between before and after the leading edge of a noise and then inputted to an integrating circuit 11. At the detection of a noise, the circuit 8 controls the interrupting frequency fC of the LPF4 and then controls the circuit 11, a sample holding circuit 12 and a gate circuit 14, so that the low frequency component is processed by integrating interpolation and the high frequency component is outputted by breaking the circuit 14 and adding the outputs of the circuits 12, 11 by an adding amplifier 15. At the absence of a noise, the circuit 14 is made and the output of the circuit 14 is added to an output of the circuit 12 by the amplifier 15.

Rating of impulse noise, in particular shooting noise, with regard to annoyance

Abstract: For impulsive noises ISO 1996 on “Assessment of noise with respect to community response” proposes to apply a penalty of 5 dB to the equivalent level Leq of the noise. In 1977 we tentatively concluded on the basis of the literature that the rating sound level (Lr, as defined in ISO 1996) for impulse sounds separated by relatively silent periods can be obtained from Lr = Limp + 10 log N − 42, where Limp = level of a single impulse, A‐weighted, 35‐ms integration time and N = number of impulses per day. This formula implies a penalty of about 12 dB to Leq of the noise. In two laboratory studies we found that the ratings for traffic noise at Leq = 45–50 dB(A) equaled those for shooting noise and pile driving noise both at about a 12‐dB‐lower Leq. A subsequent study, in which we included background noise at 35 and 55 dB(A), showed that ratings for traffic noise presented at a level 5 to 10 dB above the background equaled those for shooting noise at an equivalent level 10 dB below the level of the traffic noise...

Performance of DPSK system in impulsive atmospheric radio noise with varying impulse rates and intersymbol interference

Abstract: In the letter the performance of the DPSK system in the presence of atmospheric impulsive noise of varying impulse rates and intersymbol interference (ISI) has been evaluated. Numerical results are presented for various impulse rates and levels of ISI. The evaluated performance leads to certain interesting observations. Possible explanations for these observations are also offered.

A Code Division Multiple Access Communication System for the Low Frequency Band

Abstract: : In this thesis, a code division multiple access (CDMA) communication system for the low frequency (LF) channel is proposed, discussed and analyzed. This LF/CDMA scheme is similar to classical CDMA schemes in that K users share a channel by phase modulating their transmissions with signature sequences. Our LF/CDMA scheme is different in that each user's signature sequence set consists of M orthogonal sequences and thus log (2)M bits of information are transmitted by choosing among the signature sequences. Additionally, the users use r-phase modulation and our model includes an impulsive (non-Gaussian) noise source to model LF atmospheric noise. We derive a locally optimum (small signal) receiver structure for our LF/CDMA scheme. This receiver consists of a bandpass correlator followed by a sampler, a zero memory nonlinearity and M discrete time matched filter/correlators. We analyze the performance of this structure in combined multiple access, impulsive and Gaussian noise. When the noise is dominated by either its multiple access or Gaussian component, the receiver predominantly operates in the linear region of the nonlinearity and performance is similar to that of a linear receiver.

Computerized audio processor

Abstract: : The Computerized Audio Processor (CAP) is a computer synthesized electronic filter that removes interference from received or recorded speech signals. The CAP automatically detects and attenuates impulse sounds and tones (e.g., ignition noise, switching transients, whistles, chirps, hum, buzzes, FSK telegraphy, etc). It also attenuates wideband random noise. All operations of the CAP are fully automatic. Input signals are processed in real time, with a maximum lag of 340 msec. The CAP implements three proven signal processing techniques. One of these (IMP) virtually eliminates most loud impulse noises. A second technique (DSS) automatically detects tones and attenuates them by up to 46 dB. The third technique (INTEL) provides up to 18 dB attenuation of wideband random noise.