Extraneous Noise

Figure 3-2 Checking Extraneous Noise in the Immediate Vicinity...

Kerkut I am not clear on the behavioural side about the link between the effects of anticholinergic drugs on learning and on cutting out extraneous noise. If the animals learn more quickly, you would expect them to pay attention to what is going on. I wonder whether an explanation of the failure of your cats to respond when they are conditioned under atropine is because they are not paying attention to the signal. 

The problem of measuring infrared radiation by thermal means is compounded by thermal noise from the surroundings, bor this reason, thermal deleetors are housed in a vacuum and are carefully shielded from thermal radiation emitted by other nearby objects. To further minimize the effects of extraneous heat sources, the beam from the source is generally chopped. In this way. the analyte signal, after transduction, has the frequency of the chopper and can be separated electronically from extraneous noise, which usually varies slowly wilh time,... 

Since the ensemble average of Equation 13.19 is implemented in practice by time-averaging over a finite data-record, and since GWN is not physically realizable, many importance practical issues had to be explored in actual applications of the cross-correlation technique. To name but a few the generation of appropriate quasi-white test signals (that adequately approximate the ideal and not physically realizable GWN) the choice of input bandwidth relative to the system bandwidth the accuracy of the obtained kernel estimates as a function of input bandwidth and record length the effect of extraneous noise and experimental imperfections. An extensive study of some of these practical considerations can be found in Marmarelis and Marmarelis [1978] and in Marmarelis [1979]. 

Although this is an old and conceptually straightforward idea, it has not been widely used (except in some recent studies of chaotic dynamics of autonomous systems, where no input variable exists) because several important practical issues must be addressed in its actual implementation, for example, the selection of the appropriate coordinate variables (embedding space) and the impracticality of representation in high-dimensional spaces. If a low-dimensional embedding space can be found for the system under study, this approach can be very powerful in yielding models of strongly nonlinear systems. Secondary practical issues are the choice of an effective test input and the accuracy of the obtained results in the presence of extraneous noise. 

Male goldfish were tested in a 1.2 m square open-field maze with 4 cross-arms, a depth of 20 cm, and a volume of 160 1 (Fig. 1), Dechlorinated 20 C blank water flowed into each arm at 2 1 min (gentle flow) and out a central drain. An odor inlet merged with each blank inlet tube and aerators beside their joint outlets masked extraneous noise. Dye tests revealed an approximately linear flow with wisps of dye reaching the center in a minute and a solid cloud present in 5 min. Dye entered non-odor" arms after 10 min and drifted to the base of "non-odor arms after 15 min, although a concentration gradient was still evident. 

Just as sound studio equipment can be used to clean up extraneous noise from old recordings for remastering, it can also be used in forensic voice analysis, also called voiceprinting. In 2002, former audio engineer Tom Owen enhanced a foreign radio broadcast of Osama bin Laden and compared it with a 1998 interview to determine that bin Laden was still aUve. 

Extraneous noise denotes the noise emitted by sources other than those which have to be measured. The extraneous noise level Lp is determined while the source or sources to be measured (in general machinery or some kind) are stopped. If the... 

If possible, sound immission measurements - i.e., measurements for ascertaining the degree of nuisance experienced at particular points — should be performed at times when extraneous noise levels are low (e.g., at night). 

The lowest extraneous noise level during the measurement time is called the background level (VDI2058, Sheet 1). The background noise level Lgo is that level which is exceeded during 90% of the measurement time L95 is similarly defined. Quite often the background noise level in the neighbourhood of a cement works corresponds to the uniform level due to the noise emission from the works itself. 

In off-duty staff rooms, rest rooms and first-aid rooms the assessment level must not exceed 55dBA. For calculating the assessment level, any extraneous noise from outside the building should in principle be taken into account. 

In surroundings that are not highly reverberant and where extraneous noise levels are lower than the levels from the source under investigation, relatively few discrete points may be used, distributed uniformly over the surface. The distance from the source may be as great as 1 m. 

As the extraneous noise levels increase and/or the environment becomes more reverberant, measurements must be made progressively closer to the source in order to maintain an acceptable level of uncertainty in the measurements. This also requires more measurement points to be used because of the increase in the spatial variation of the intensify distribution. 

C) Distance between source and probe. Generally, the greater the extraneous noise and the more reverberant the environment then the closer should be the probe to the source. In extreme cases the probe may be only a few centimeters from the source surface in order to improve the signal-to-noise ratio. This is normally frowned upon when using conventional sound level meters because measurements... 

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