Narrow band noise

Figure 2.1 (according to [Zwicker, 1982]) shows a masked threshold derived from the threshold in quiet and the masking effect of a narrow band noise (1 kHz, 60 dB sound pressure level masker not indicated in the figure). All signals with a level below... 

Figure 2.1 Masked thresholds Masker narrow band noise at 250 Hz, 1 kHz, 4 kHz (Reprinted from [Herre, 1995] 1995, courtesy of the author)...

Masked thresholds Masker narrow band noise at 250 Hz, 1 kHz, 4... 

From this equation, Ey (T)/E- -(0) increases monotonically from unity at T=0K to 1,33 at T=Tc. This behaviour differs from one observed in the CDW materials, where Ey exhibits a divergence at T=Tc and a minimum slightly below Tq, which results from an increase in Ey at low temperatures, due to phase fluctuations. Hence, one should expect to observe similar properties of the SDW current-carrying state to ones of the CDW nonlinear current-voltage characteristics, accompanied by broad and narrow band noise, with sharp threshold fields, frequency-dependent conductivity, interference effects between the ac voltage generated in the sample, and an external rf field, hysteresis and memory effects etc. 

Two essential features of the sliding CDW mode seem to be rather well established for the SDW mode, too. Non-ohmic electrical transport sets in above a finite threshold field, and a collective mode contribution is evident at finite frequencies in the spin-density wave ground state. These features are also in qualitative agreement with theoretical models. However, important differences are observed, like the temperature dependence of the threshold field and the relaxation time and effective mass of the collective mode. Further experiments are required to establish details of this behaviour, as well as to search for other nonlinear effects,like broad and narrow-band noise, hysteresis and memory effects etc. 

Coloured noise, narrow band noise and periodic impulsive noise are usually modeled as background noise because they remain stationary from seconds to even hours. Periodic impulsive noise synchronous to the mains and asynchronous impulsive noise may cause bit or burst errors over the transmission, although they are time variant. A complete theoretical analysis on shown noises in Figure 2 can be found on [5, 6,11,12,13]. 

The control requirements for the previously described coloured noise, narrow band noise, periodic impnilsive noise and asynchronous impulsive noise, can be separately analyzed in two different scenarios. 

Narrow band noise is restricted to a narrow range of frequencies. Examples include noise from various kinds of pumps, drilling tools, and hoists. 

Excessive axis-specific narrow band noise is less common, but can occur if there is excessive... 

The entry reviews the fundamental theory of passive tuned mass dampers and parametric pendulum dampers as well as the major developments of the theory in the last hundred years. The motion of the primary mass subjected to a deterministic or stochastic excitation is considered. The principle parameters of the system influencing the dynamics of the primary mass such as mass and frequency ratios are identified. Different formulas derived by a number of authors based on the various optimization criteria are presented for optimal tuning of a damper. The effectiveness of a parametric pendulum tuned mass damper, which interaction with the primary mass is completely different from a conventional tuned mass damper, is discussed. The optimal values of the PPD damping are found numerically for the primary system subjected to a narrow-band noise. Vibrations of the primary mass with a parametric pendulum... 

Figure 2.41. Narrow band noise frequency as a function of the excess current density in Per2Pt(mnt)2. (Reproduced by permission of American Physical Society, from ref. 94.)...

Another area of concern is the Q of the filter at self-resonance. If the Q is too high, or in other words, the damping factor is too low, the filter will actually generate noise in the form of narrow-band ringing. This can be dealt with during the design. 

The links between levels of exposure and inconvenience caused by ventilation noise are described in an investigation carried out on office workers.- Technical measurements and analyses of the ventilation noise at 155 typical office workplaces were in this study combined with assessments by the office workers of the level of disturbance that they experienced, the effect on working performance, fatigue, stress-related pain, and headaches. The average noise level was about 40 dB(A) at two of the workplaces, while it was about 35 dB(A) at two others. It emerged from rhe narrow-band analyses that the sound pressure levels of rhe infrasound were not in any event of an order that this type of sound frequencies (below 20 Hz) could contribute to any disturbance effects. Any steps taken to counter the sound frequencies of the ventilation noise under 50 Hz, i.e., the point of btersection between the threshold curve of auditory perception and the spectral level distribution curve of... 

The continuous wave technique has a definite advantage over the other techniques a very narrow band of frequencies is needed to transmit the information. The pulse techniques, on the contrary, use a large band of frequencies, and the various noises, pump noises in particular, are more difficult to eliminate. 

If further resolution is necessary one-third octave filters can be used but the number of required measurements is most unwieldy. It may be necessary to record the noise onto tape loops for the repeated re-analysis that is necessary. One-third octave filters are commonly used for building acoustics, and narrow-band real-time analysis can be employed. This is the fastest of the methods and is the most suitable for transient noises. Narrow-band analysis uses a VDU to show the graphical results of the fast Fourier transform and can also display octave or one-third octave bar graphs. 

Computers may be used for noise analysis when connected to dedicated hardware devices. One machine incorporates a narrow-band analyzer, octave and one-third octaves with all the features of an environmental noise analyzer. These devices cost much less than purchasing all the dedicated instmments separately. They may be obtained in portable form but are rarely weatherproofed for outdoor use. 

Considerations of the signal-to-noise ratio usually dictate the use of the technique of narrow-banding in nuclear resonance. The modulation magnetic field is reduced to small amplitude compared to the resonance line width as shown in Fig. 3. 

We have found it to be generally true that the constraint of minimum negativity produces results much superior to those obtained with the constraint of finite extent. The minimum-negativity procedure has also been found to be extraordinarily insensitive to noise and other error. This is contrasted with the equations resulting from the constraint of finite extent, for which usually only a narrow band of coefficients may be permitted restoration to achieve a stable solution. The best overall results, however, are obtained with a combination of the two constraints. 

We discuss in Section IX techniques for constructing a reflection mode spectrometer based on quasioptical techniques that will have a receiver input bandwidth A/ = 25 GHz. The quasioptical component that accomplishes this function is a Polarization Transforming Reflector (PTR) discussed in Howard et al. (1986) We use the PTR as a wave plate that rejects noise components outside of a narrow band. We discuss this point further in Section IX. Based on Eq. (78), this should allow a further reduction in Frt, min factor of 2 compared to the current spectrometer. We may... 

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