Noise impulse

Impulse noise Noise of short duration, i.e., three seconds or less. Also called impact noise. 

Shields used to provide protection from intentional detonation of ammunition are to be designed to prevent exposure of operating personnel to impulse noise levels exceeding 140 decibels. 

Autoregressive (AR) model-based Click Detection. In this method ([Vaseghi and Rayner, 1988, Vaseghi, 1988, Vaseghi and Rayner, 1990]) the underlying audio data. v n is assumed to be drawn from a short-term stationary autoregressive (AR) process (see equation (4.1)). The AR model parameters a and the excitation variance <52e are estimated from the corrupted data x[n using some procedure robust to impulsive noise, such as the M-estimator (see section 4.2). 

Carrey and Buckner, 1976] Carrey, M. J. and Buckner, I. (1976). A system for reducing impulsive noise on gramophone reproduction equipment. The Radio Electronic Engineer, 50(7) 331-336. 

Hicks and Godsill, 1994] Hicks, C. M. and Godsill, S. J. (1994). A 2-channel approach to the removal of impulsive noise from archived recordings. In Proc. IEEE Int. Conf. Acoust., Speech and Signal Proc, volume 2, pages 213-216, Adelaide, australia. 

Montresor et al., 1990] Montresor, S., Valiere, J. C., and Baudry, M. (1990). Detection et Suppression de Bruits Impulsionnels Applique a la Restauration d Enregistrements Anciens (Detection and suppression of Impulsive noise applied... 

Vaseghi and Rayner, 1990] Vaseghi, S. V. and Rayner, P. J. W. (1990). Detection and suppression of impulsive noise in speech communication systems. IEE Proceedings, Parti, 137(1) 38—46. 

The API Medical Research Report EA 7301. (Ref 2) This document dates from 1973 and sets a limit of 115dB(A) for steady sound and 140 dB (peak) for impulsive noise. These limits were based on the data in the US OSHA 1970 Act. 

Impulse noise — is an unwanted interference of a signal by random energy spikes having random amplitude and spectral content. 

Impulse Noise Analysis Results. ANITA-lite measured about 130,000 distinct events, with an approximate rate of 5 events per minute. Fig. 6 shows examples of the major classes of impulsive noise encountered. The vast majority of triggered events are due to local payload interference such as switching noise from the Support Instrument Package. The duration of this class of events exceeds several hundred nanoseconds and a few events exhibit circular polarization for a portion of the pulse. The bottom two panes show an example of a synthetic pulse injected into the data stream to simulate a true signal event. The pulse is coherent and aligned across all channels. Preliminary studies of event selection procedures were conducted. They yield no passing events, while 97% of simulated Askaryan-induced impulses with amplitude 5<7 above noise survive (Miocinovic et al., 2004). 

Impulse noise should be limited to 140 dBA per eight-hour day for continuous exposure. 

Despite its ability to faithfiilly mimic the target and transition patterns of natural speech, standard LP synthesis has a significant unnatural quality to it, often impressionisticly described as buzzy or metallic sounding. Recall that while we measured the vocal tract model parameters directly from real speech, we still used an explicit impulse/noise model for the source. As we will now see, it is this, and specifically the interaction of this with the filter, which creates the unnaturalness. 

MFCC synthesis is a technique which attempts to S3mthesise from a representation that we use because of its statistical modelling properties. A completely accurate S3mthesis from this is not possible, but it is possible to perform fairly accurate vocal tract filter reconstruction. Basic techniques use an impulse/noise excitation method, while more advanced techniques attempt a complex parameterisation of the source. 

The source for vowels and voiced consonants can be generated either as an explicit time-domain periodic function, of the type described in Section 11.4.2, or by an impulse sequence that is fed into a glottal LTI filter. For obstruent sounds a random-noise generator is used. Sounds such as voiced fricatives use both sources. If we adopt the impulse/filter approach, we see that in fact these sources are equivalent to those of the classical impulse/noise LP model (Section 12.6.4). One difference between the impulse/glottal-filter source and LP models is that in the impulse/glottal-filter model the voiced source is... 

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