Noise suppression, methods

Plant layout and noise suppression material are two general noise abatement methods. Plant layout does not affect noise levels at any given point however, noise can be abated by screening off a section of the plant. An example of this is to orient cooling towers with their closed faces toward the critical location. This method must also consider wind direction to balance air draft. Tankage can be located to act as a noise screen. 

A collaborative effort between The University of Mississippi (Seiner), Florida State University (Krothapalli), and Combustion Research and Flow Technology — CRAFT (Dash) has recently been initiated that includes all phases that are required for completion of a successful noise-reduction program. To enable projection of model-scale laboratory acoustic data to full scale, one-tenth-scale models have been constructed. The primary methods being investigated for noise suppression involve the use of micro-air-jet injection, water-drop injection, and modification of nozzle divergent flaps into corrugated shapes with chevrons. All of these concepts are known to produce little impact on aeroper-formance. 

Development of a successful noise-reduction program requires the acquisition of narrowband acoustic data using ground-based microphones. It is only with this type of data that one can identify the jet aeroacoustic sources that drive the particular method to be adopted for noise suppression. In particular, at the engine power settings and engine exhaust temperatures of the FCLP, the predominant jet-noise sources are related to highly efficient processes associated with Mach wave emission and shock noise. 

Specialized knowledge of the material to be used and its most effective method of application is required to ensure that noise suppression and control techniques are effective. It is advisable to call in specialists. 

F. Ni, G. C. Levy, and H. A. Scheraga, J. Magn. Reson., 66, 385 (1986). Simultaneous Resolution Enhancement Noise Suppression in NMR Signal Processing by Combined Use of Maximum Entropy and Fourier Self-Deconvolution Methods. 

The rest of the book is dedicated to the above quoted methods of photodetector enhancement. It is divided into two parts. One of them analyzes different methods to optimize the photodetector input, i.e., to perform its optical improvement, while the other part is denoted to nonequihbrium methods of noise suppression. 

The nonequilibrium methods are the other part of the reply to the question of noise suppression. They proved themselves a means to suppress Auger recombination, but also for a significant part the Auger generation as well. Each... 

These spectra demonstrate that with the multiselective method a clean separation of the subspectra of the three independent spin systems may be achieved. They furthermore prove that - compared to the basic ID TOCSY experiment - spectra of the same quality with respect to the suppression of residual signals originating from the other spin systems and with respect to the signal-to-noise ratios can be measured. 

It may be necessary to mention the relationship between PFG and D-HMBC. PFG is an especially suitable method to observe HMBC spectra with suppressed ti noise, and enables to detect very weak cross peaks which could... 

Typically, t(co) is small for co large. A spectrometer suppresses high frequencies. If the data i(x) have appreciable noise content at those frequencies, it is certain that the restored object will show the noise in a more-pronounced way. It is clearly not possible to restore frequencies beyond the band limit Q by this method when such a limit exists. (Optical spectrometers having sine or sine-squared response-function components do indeed band-limit the data.) Furthermore, where the frequencies are strongly suppressed, the signal-to-noise ratio is poor, and T(cu) will amplify mainly the noise, thus producing a noisy and unusable object estimate. 

An amplitude bound has the added virtue of producing solutions having reduced noise sensitivity, fewer artifacts, superior resolution, and possible bandwidth extrapolation. In contrast, methods having an output that is linear in the irradiance data i(x) either produce artifacts or trade off resolution to suppress artifacts. If a bound makes physical sense and can be computationally afforded, use it. Simple clipping of unphysical parts does not always work well, however. Subtle techniques may be more desirable. 

When using the Ephraim and Malah suppression rule, it appears that it is still useful to limit the attenuation in order to avoid the reappearance of the musical noise phenomenon at low-levels. In practice, the average attenuation applied to the noisy part can be easily controlled via one of the parameters of the method (see [Cappe,... 

Several techniques have been proposed for modifying the shape of the short-time spectrum so as to emphasize those portions deemed to be important for speech perception or to reduce the amplitude of those portions assumed to be noise. One approach is adaptive comb filtering[Lim et al., 1978], In this method, the fundamental frequency of voiced speech sounds is estimated, and a comb fdter is then constructed to pass signal power in the regions of the pitch harmonics and to suppress power in the valleys in between. Experimental results with normal-hearing subjects, however, have shown no significant improvement in intelligibility with this type of system [Perlmutter et al., 1977][Lim et al., 1978],... 

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