Noise suppression

Any protuberance on the bowl will induce noise, and the faster the bowl then the louder will be the noise. Impellers at the cake discharge are major producers of noise. Even bolt heads in the bowl can emit noise. Recessing the bolts helps to abate noise, but to improve the abatement one technique is to cover all major bolt heads with metal rings secured by much smaller flush bolts. These can be smaller as they do not have such a great load to bear. This action is more frequently taken on the larger high-speed decanters. 

Decanters open to the atmosphere produce more noise than dosed ones, and thus closing or sealing the casing outlets reduces noise levels. 

Resonant vibration of various static components, particularly in the casing, can produce irritating noises and thus care has to be taken to avoid flimsy and unsupported structures. 

The ultimate noise suppression is the use of a purposely constructed noise suppression hood. These hoods can be very effective, but they do have 

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Perception and Entropy Inspired Ultrasonic Grain Noise Suppression, Using Noncoherent Detector Statistics. 

The main goal of ultrasonic grain noise suppression in material flaw detection is to improve the perceptual possibilities of the operator to observe defect echoes. The suppression is defined as perceptually ideal when a received signal (or image) which contains echoes buried in noise is filtered to yield nonzero values only at the positions of the defect echoes. 

Filters that output noncoherent detector statistics have, in our recent work [1], shown to be very powerful for grain noise suppression in ultrasonics. However, such filters require the operator to carefully specify a transient prototype as a model of the defect echoes which should be detected. Here a new approach is presented, based on the above ideas about perception, which eliminates the need for the operator to manually specify a defect prototype. 

Preprocessing allows the enhancement of the visual quality of the image and noise suppression... 

This research examines the feasibility of a technique based upon the CT principle using a microfocus X-ray source with an image intensifier while the examined object is being rotated The attainable enlargement is up to 200. The data to be processed is collected from the whole surface of the image intensifier by a frame grabber and noise suppression is performed. 

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. 

B. Walczak and D.L.Massart, Tutorial Noise suppression and signal compression using the wavelet packet transform. Chemom. Intell. Lab. Syst., 36 (1997) 81-94. 

L0 noise suppression Alixer noise temperature 900 K (DS8) -System noise temperature 1360 K (DSB) -Alixer conversion loss 6 dB (DSB) -20mWat 80 GHz required inW at 160 GHz generated by D162 >TF bandwidth to > 20 GHz... 

Noise is a serious problem where z(co) is small. We see that the estimate 6(cd) carries with it none of the sensible noise treatment that modified filters like those of the Wiener type provide. We may, however, supply the required noise suppression between iterations by smoothing. The polynomial filters described in Section III.C.5, for example, may be used. Very little has been done, however, to determine how suppression might be accomplished optimally. Usually it is treated in an ad hoc way. 

The dual slope converter is superior to the successive approximation type in many respects, e.g. in having an automatic zero capability, good noise suppression, and accuracy which is not affected by capacitor rating or clock frequency. However, the use of the latter type of converter is limited because of its slow conversion time (about 30 ms). 

Standard examples of noise-suppression rules include the so-called Wienei6 suppression rule, the power-subtraction (see Figure 4.16), the spectral subtraction [Boll, 1979, Lim and Oppenheim, 1979, McAulay and Malpass, 1980, Vary, 1985], as well as several families of parametric suppression curves [Lim and Oppenheim, 1979, Moorer and Berger, 1986, Etter and Moschytz, 1994],... 

Petersen and Boll, 1981] Petersen, T. L. and Boll, S. F. (1981). Acoustic noise suppression in the context of a perceptual model. In Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing, volume 1086-1088. 

Vary, 1985] Vary, P, (1985). Noise suppression by spectral magnitude estimation -Mechanism and theoretical limits. Signal Processing, 8(4) 387-400. 

Background noise suppression by short- time spectral attenuation 165... 

Figure 4.15 Background noise suppression by short-time spectral attenuation...

The result of the noise suppression rule can always be interpreted as the application of a real gain (1 ip, Qk) to each bin of the short-time transform X(p, Qk) of the noisy signal. Usually, this gain corresponds to an attenuation , ie. lies between 0 and 1. For most suppression rules, G(p,Qk) depends only on the power level of the noisy signal measured at the same bin X (p, Qk) 2 and on an estimate of the power of the noise at the frequency 0, Pv(Qk) = E V(p, Qk) 2 (which does not depend on the time index p because of the noise stationarity). In the following, the ratio Q p, Qk) = X(p, Qk) 2 /Pv(Qf. ) will be referred to as the relative signal level. Note... 

Two areas of signal processing research in cochlear implants are coding strategies for multi-electrode excitation and the development of noise-suppression systems. One of the problems in cochlear implants is that there is a large spread of the electrical stimulation within the cochlea. Because of this, simultaneous electrical pulses at... 

Boll, 1991] Boll, S. F. (1991). Speech enhancement in the 1980s noise suppression with pattern matching. In Furui, S. and Sondhi, M., editors, Advances in Speech Signal Processing, chapter 10, pages 309-325. Marcel Dekker. 

Hochberg et al., 1992] Hochberg, I., Boothroyd, A., Weiss, M., and Heilman, S. (1992). Effects of noise suppression on speech perception by cochlear implant users. Ear and Hearing, 13 263-271. 

McAulay and Malpass, 1980] McAulay, R. J. and Malpass, M. L. (1980). Speech enhancement using a soft-decision noise suppression filter. IEEE Trans. Acoust., Speech, Signal Processing, 28(2) 137-145. 

In this section, more general excitation patterns will be discussed, which allow for tailored deconvolutable excitations with high spectral power densities. Periodic amplitude modulation with a single frequency has been proposed in the literature [73]. It is well suited for noise suppression by lock-in detection, but in practice it suffers from stability problems during the slow frequency sweep. 

The minimum U = 1 is assumed for a constant white power spectrum with X[k] 2 = N. All deviations from the constant power spectrum increase the integral noise amplification U. They may, however, be useful for noise suppression at... 

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