Read noise

Noise monitoring equipment, like air monitoring equipment, should be used, stored, and maintained in aeeordanee with manufaeturer ree-ommendations. Noise instrumentation is typieally ealibrated prior to use for eaeh shift and eheeked at the end of the shift to determine aeeuraey Noise readings also should be reeorded in a log and should beeome part of the permanent site reeord. 

Weighting can be imposed on noise readings, which corresponds to the inverse of the equal-loudness contours. If this weighting is used, all readings that are numerically equal will sound equally loud, regardless of frequency. 

Figure 21. Noise spectrum of detector amplifiers. Note that both axes have logarithmic scale. There are two main components of noise - the white noise which is present at all frequencies, and the 1// noise that is dominant at low frequencies. 1// noise has a fractal structure and is seen in many physical systems. The bandpass of a measurement decreases for slower readout, and the readout noise will correspondingly decrease. A limit to reduction in readout noise is reached at the knee of the noise spectrum (where white noise equals l/f noise) - reading slower than the frequency knee will not decrease readout noise.

The LISN sensitivity increases (at the rate of 10 dB/decade). So we would start getting higher and higher noise readings. 

The system is calibrated by exposure of one scintillator to white noise In the form of a Co source. Both multifilter inputs are connected to the one detector output, and measurements are taken as described above. For each band, the reading taken on a reactor run is divided by the white-noise reading, calibrating out equipment frequency response. 

Figure 7 Exploiting the dichroism of holes for a low-noise reading process. N denotes the number density of absorbers with their dipole moments in the direction 0. is the polarizer, P2 the analyser.

This dye shows high absorption at wavelengths between 780 and 830 nm, and a reflectivity of about 30%. This signal-to-noise ratio is about 50 dB with high consistency, even after lO read cycles (14). A disadvantage is the high expenditure for the synthesis of these derivatives due to low yield (15). 

Fig. 16. Maximum achievable signal-to-noise ratio (SNR) on read-out of different writable optical data storage systems as a function of the writing energy (laser power) (121). SQS = Organic dye system (WORM) PC = phase change system (TeSeSb) MO = magnetooptical system (GbTbFe). See text.

Noise monitoring is usually located in the HASP as part of the monitoring program. Noise monitoring should be performed in accordance with acceptable practices. Typically, noise levels are monitored in the field with either a Type I or Type II sound level meter (SLM). Noise dosimeter readings can also be obtained to determine the percent (%) noise dose. Noise levels and % doses measured are then compared to limits listed in OSHA standard 29 CFR 1910.95, Hearing Conservation [3]. 

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Portable sound level meters are also available which can measure percentiles. These either hold the results in a memory which can be separately interrogated or may be connected to a computer for a printout. Larger machines (known as environmental noise analyzers) are available which can record percentiles and Leq readings and produce a printout. These are resistant to weather and can be left on-site for up to a week. 

Von Neumann s and Brilloun s assertions are both certainly very plausible ones, in view of the fact that each mechanical degree of freedom used to store one bit of information (such as a capacitor, for example) involves at least an amount of kT of thermal noise which must then apparently be overcome to reliably read or manipulate the given bit of information [benn82]. We have inserted the word apparently in quotes, however, because this supposition is now known to be false ... 

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