Type of noise

Today there is a pronounced need to take more effective measures against this type of noise. The problem is complicated, however, by the fact that these measures in many instances are unilaterally targered at achieving a lowering of the dB(A) level, which in many cases has resulted in only a marginal restriction of the inconvenience, or even none at all. 

The extent to which a ventilation noise is perceived as disturbing depends not only on its dB(A) level, but also on the spectral distribution and the presence of tones or intermittent components in the noise. From an experiment carried out on respondents exposed to ventilation noises with different characteristics in a simulated office room, it emerged that the highest acceptable level was about 7 dB higher for ventilation noise with a superimposed tone at 30 Fiz than for other types of noise. In another experiment, it was found that the tolerance level was much higher for a tone than for a noise at 100 Hz, whereas the opposite tendency applied at 1000 Hz. ... 

There are three different types of detector noise, short term noise, long term noise and drift. These sources of noise combine together to give the composite noise of the detector. The different types of noise are depicted in figure 3. 

Ideally, any procedure for signal enhancement should be preceded by a characterization of the noise and the deterministic part of the signal. Spectrum (a) in Fig. 40.18 is the power spectrum of white noise which contains all frequencies with approximately the same power. Examples of white noise are shot noise in photomultiplier tubes and thermal noise occurring in resistors. In spectrum (b), the power (and thus the magnitude of the Fourier coefficients) is inversely proportional to the frequency (amplitude 1/v). This type of noise is often called 1//... 

Fig. 40.18. Noise characterisation in the frequency domain. The power spectrum IF(v)l of three types of noise, (a) White noise, (b) Flicker or 1//noise, (c) Interference noise.

Noise is generally added to the signal function the types of noise are schematically shown in Fig. 3.7. 

Fig. 3.7. Power spectra of the most important types of noise (schematic representation in the frequency domain)... 

We will be doing this exercise during the course of the next few chapters. We will consider each of these types of noise one at a time. We will start from first principles, derive the appropriate expressions and deal with them in a completely rigorous manner. During the course of this we will compare out results with the ones in the literature and see where the standard derivations (NOT deviations ) depart from our presentation. 

Chapter 40 is based on reference [1], In this chapter we brought up the question of how various types of noise are related to the noise characteristics of the spectra one observes. In this chapter, and in the thirteen subsequent chapters (41 through 53), we will derive the expressions for the various situations that arise these situations have been described in greater detail within Chapter 40. 

Now it is time to examine the effect of a more realistic type of noise than we have been considering so far. In a real situation, of course, where many readings may be... 

Type of noise Constant detector Shot noise Scintillation noise... 

When the noise is small the multiplication factor approaches unity, as we would expect. As we have seen for the previous two types of noise we considered, the nonlinearity in the computation of transmittance causes the expected value of the computed transmittance to increase as the energy approaches zero, and then decrease again. For the type of noise we are currently considering, however, the situation is complicated by the truncation of the distribution, as we have discussed, so that when only the tail of the distribution is available (i.e., when the distribution is cut off at +3 standard deviations), the character changes from that seen when most of the distribution is used. 

THE THREE STAGES OF PRODUCT DEVELOPMENT AND THE POSSIBILITIES OF COUNTERMEASURES AGAINST VARIOUS TYPES OF NOISE, WITH O - COUNTERMEASURES POSSIBLE AND X - COUNTERMEASURES IMPOSSIBLE... 

The development cycle of a product can be separated into three stages, which are product design, process design and manufacturing. In Table 4.1, copied from reference [8], is shown in what stage countermeasures against the three types of noise factors can be taken. As can be seen countermen-... 

The second contributor to Eq. (53) has to do with the type of noise assumed to be present. To keep things simple, we shall assume it to be additive and independent Gaussian but with generally position-dependent variance e . This describes, for example, Johnson noise and other noise types that enter into the output of the spectrometer. Thus, we have as the probability PN of noise... 

Pyrotechnic compositions can produce two types of noise a loud explosive bang or a whistle. The explosive bang is achieved by placing a... 

Figure 20-31 Three types of noise in electrical instruments. White noise is always present. A beam chopping frequency can be selected to reduce 1/f noise and line noise to insignificant values.

More precisely, die quantity displayed is the signal power estimated from 10ms frames. As die power spectral densities of die two types of noise exhibit a strong peak at the null frequency, the two noises were pre-whitened by use of an all-pole filter [Cappe, 1991]. This pre-processing guarantees that the noise autocorrelation functions decay sufficiently fast to obtain a robust power estimate even with short frame durations [Kay, 1993]. 

Figure 7.14 Recognized types of noise short-term noise, long-term noise, and drift.

Types of noise. Any electronic system contains (and produces) many types of noise. Basically two aspects of noise can be differentiated ... 

It is important to notice that, in real-life applications, the actual number of projections must always be greater (often much greater) than the theoretical minimum, because of the need to compensate the inevitable loss of information which is produced by various types of noise. It is also important to notice that the theoretical minimum obtained with non-algebraic methods (Crowther et al., 1970) is never inferior to the algebraic minimum. Equation 3.5, in other words, is the lowest possible estimate of the minimum number of projections that are required for a complete reconstruction of any given structure. 

There are many types of noise, which interfere with the detection or accumulation of signal. The signal-to-noise ratio (S/N) is typically estimated in decibels If Is is the intensity of the signal, and IN is the intensity of the noise at that same frequency, then... 

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