White Noise Generator Research Articles

A simple shaker table for seismometer calibration

A unique and simple shaker table (shake table or shaking table), designed, constructed, and installed at the Hawaii Institute of Geophysics, has proven to be a valuable aid in testing and calibrating short period seismometers, as well as ocean bottom and ocean sub-bottom seismometer/tilt meter packages. It consists of a platform suspended in a stairwell by a single elastic cord (10 m extended length) driven by GeoSpace HS-10 geophones. Platform motion is monitored by orthogonal reference geophones and tilt meters. The relatively low natural periods of the platform, about 1.9 sec vertical and 6.5 sec horizontal, provide sufficient isolation from local vibrations that calibration can be made near operational amplitudes. Vertical or horizontal driver geophones can be driven by a commercial signal generator or white noise generator, or from magnetic tape output. The table can also be tilted with respect to the drivers to determine tilt tolerances and to calibrate tilt meters. A Hewlett-Packard 3582-A spectrum analyzer, used to analyze both reference and output signals, provides near real-time system cabibration and is an efficient means for investigating parasitic system resonances. The analyzer can also provide a white noise signal source to the driver geophones.

Device for the induction of specific brain wave patterns

Brain wave patterns associated with relaxed and meditative states in a subject are gradually induced without deleterious chemical or neurological side effects. A white noise generator (11) has the spectral noise density of its output signal modulated in a manner similar to the brain wave patterns by a switching transistor (18) within a spectrum modulator (12). The modulated white noise signal is amplified by output amplifier (13) and converted to an audio signal by acoustic transducer (14). Ramp generator (16) gradually increases the voltage received by and resultant output frequency of voltage controlled oscillator (17) whereby switching transistor (18) periodically shunts the high frequency components of the white noise signal to ground.

Resolution improvement in an analog‐to‐digital converter by the superposed dither signal

AbstractThis paper discusses a method to improve the resolution of an analog‐to‐digital (A‐D) converter to detect differences less than 1 LSB (least significant bit) in the input signal. Resolution is improved by superposing dither on the input signal and averaging over many measurements. The theory and experimental verification for this method are described.This analysis calculates numerically the expectation value of the result of A‐D conversion and the expectation value of the variance, with the dither superposed on the input signal. The results show that for larger amplitude of dither, the expectation value of A‐D conversion comes closer to the real value, and the expectation value of the variance becomes larger.The relation between the amplitude of dither and the improvement of resolution is calculated as a function of the number of measurements. For example, when the number of measurements is 100 and the amplitude of dither is 0.4 LSB, the resolution can be improved to 0.05 LSB.This analysis is verified experimentally by using a white noise generator as a dither source, dc voltage standard as a signal source, and a transient recorder as an A‐D converter.

Stochastic forcing models of climate variability

Hasselmann (1976) has recently proposed a stochastic model of climate variability where climatic changes are caused by the intrinsic variability of the weather fluctuations. The complete atmosphere--ocean--cryosphere-land system is separated into long time scale cl imate components (mainly the ocean and the cryosphere) and short time scale wea ther components (mainly the atmosphere). The weather components exhibit stochastic fluctuations with a dominant t ime scale of a few days, reflecting instabilities of the atmospheric circulation. Because of their much larger time scale, the climate components respond essentially as integrators of the atmospheric forcing, which acts as an internal white noise generator. The random-walk climate fluctuations that develop have a variance which grows linearly with time, until feedback processes become important and lead eventually to a statistically stationary climate state. A red frequency spectrum is predicted for the climate variance, in general agreement with observations over a broad range of time scales, as reviewed below (see also Mitchell, 1976). The general theory is given in Hasselmann (1976). Here we shall introduce the formalism in the simpler context of sea surface temperature anomalies, and present new comparisons of the model predictions with observations in the North Pacific. It is shown that a single model reproduces the principal features and the seasonal variability of the large-scale sea-surface temperature anomalies observed in mid-latitudes. Other applications of the stochastic climate models are then reviewed. Quasi-geostraphic motions in the ocean interior and yearly and zonally averaged world temperature fluctuations induced by the natural variability of the atmosphere are discussed. The magnitude of

The subjective influence produced by white noise

The effects on people of noise produced indoors is assessed. The annoyance produced by white noise is evaluated here, exclusively as a psychological aspect. The annoyance is defined as a function of perceived noise level (Noys) plus exposition time plus psychological and sociological factors. Statistical procedures were used in the designing of experiments. such as Latin squares. Eighty persons were used as subjects in this evaluation and seven kitchen machines were used as noise sources plus one white noise generator, giving a total of eight sources.

Time shipt evoked potentials (TSEPs): Method and basic results

A simple technique for generating averaged evoked potentials to auditory signals that appear to move in space is described. Shifts in the apparent location of the signal were created by digitally delaying the output of a white noise generator with a minicomputer. The two channels were reconverted to two analog signals and presented binaurally through headphones. Shifts in the apparent location of the signal produced a time shifted evoked potential (TSEP) that was not present during monaural control runs. TSEP amplitudes were largest near the vertex and varied as a function of the presentation format.

Synthesis of linear stochastic signals in identification problems

Stationary stochastic inputs are generated from linear processes of the autoregressive moving average type. Since the spectral density of such an input process is nonzero everywhere, this belongs to the class of admissible signals satisfying identifiability requirements. A characterization of the optimal signals is obtained in terms of their spectral densities using the results on asymptotic eigenvalue distribution of Toeplitz matrices. These signals belong to the general class of random inputs that can be generated using standard instrumentation consisting of delay lines and a white noise generator.

Squid Axon Membrane Response to White Noise Stimulation

The current from a white noise generator was applied as a stimulus to a space-clamped squid axon in double sucrose gap. The membrane current and the voltage response of the membrane were then amplified, recorded on magnetic tape, and the stimulus was cross-correlated with the response. With subthreshold stimuli, a cross-correlation function resembling that obtained from a resonant parallel circuit is obtained. As the intensity of the input noise is increased, the cross-correlation function resembles that obtained from a less damped oscillatory circuit. When the noise intensity is further increased so that an appreciable frequency of action potentials is observed, an additional component appears in the experimental cross-correlogram. The subthreshold cross-correlogram is analyzed theoretically in terms of the linearized Hodgkin-Huxley equations. The subthreshold axon approximates a parallel resonant circuit. The circuit parameters are temperature dependent, with resonant frequency varying from approximately 100 Hz at 10 degrees C to approximately 250 Hz at 20 degrees C. The Q(10) of the resonant frequency is equal to 1.9. These values are in agreement with values found previously for subthreshold oscillations following a single action potential.

Synthesis of low-frequency noise for use in biological experiments.

A simple technique is described for the generation of white noise having sufficient power below 10 Hz to be useful in biological experiments.

Some determinants of performance in a commercially available one-way avoidance chamber

Apparatus The Ss were tested in a Lafayette Instrument Co. Model 85200 one-way avoidance chamber measuring 9 x 8 x 8lA in. The chamber has clear Plexiglas top and sides, a grid floor with 15 shock bars, and a stainless steel back. The front is stainless steel also and has a door 3'h in. above the grid floor. When a motor is activated, the door retracts and exposes a stainless steel platform, onto which the S can jump to either avoid or escape footshock. The floor of this safe compartment is mounted on a microswitch, which terminates the trial when activated. An Eico Model 378 oscillator provides a I-kHz tone to a 4-in. speaker placed next to one of the side panels of the chamber. A Grason-Stadler Model 901 B white noise generator delivers masking noise to another speaker underneath the test table. The 1-mA footshock was delivered by a Grason-Stadler Model700 shock generator.

Automatic Impedance Measurements Using Thermal Noise Analysis

An apparatus permitting measurements of current and voltage thermal noise of two terminal devices has been built using a correlator amplifier and a controlled amplitude white noise generator. It allows accurate determinations of device impedance components, especially of nonlinear devices such as thin ferroelectric capacitors.

ディジタル計算機による帯域制限白色雑音の発生

ディジタル計算機による帯域制限白色雑音の発生

Analysis of the Switched Self-Balancing Comparsion Radiometer

Analysis of the switched self-balancing comparison radiometer with coupling between the channels is given. The comparison source is a stationary, zero-mean white noise generator of known spectral density. An expression for the power spectrum at the output of the radiometer is derived. It is shown that measurement errors due to interchannel coupling can be corrected by phase switching. Radiometer sensitivity is also calculated. The switched version of the radiometer has been simulated at low frequencies and is under construction at X-band.

Paper 10: Laboratory Simulation of Field Load Spectrum

This paper presents details of a laboratory simulation of field load spectrum program developed and being implemented at the Advanced Project Engineering Division of Massey-Ferguson. The aspects of data acquisition, data reduction, and laboratory simulation are discussed. Data acquisition includes calibration of transducers and indexing or control pulse coding of the analog tape to assist subsequent processing of data on a digital computer system. Data reduction involves analog-to-digital conversion, binary conversion, calibration, collection of useful portions of raw digitized data, transformation of data to their proper engineering units and analyses of data in time and/or frequency domains. Laboratory simulation is accomplished in two basic forms: (1) Controlled dynamometer testing, utilizing weighted composite load–frequency histograms derived from the field data, is preferred for complex mechanical systems with high inertia undergoing variety of loads with severe extremes. (2) Shaker testing, utilizing electromagnetic and electrohydraulic shakers, is preferred for structural testing of entire mechanical systems or their components by providing a duplication of field vibrations through a closed-loop magnetic tape control. Power spectral density analyses of the random signals (involving input forcing functions to the mechanical systems) are performed to correct for the frequency response characteristics of the shaker systems and the mountings used for the testing. The pertinent load spectrums can also be synthesized from their corresponding power spectra by using a white noise generator as the input device in place of the closed-loop analog tape playback system.

A low-frequency gaussian white-noise generator

The various methods of generating low-frequency noise are discussed. The merits of using a binary random signal, particularly the binary random square wave, as a noise source are considered, The advantages of applying the binary random signal to a low-pass filter to produce white gaussian noise are pointed out. A general method of designing filters which compensate for the fall in spectral response of the binary signal over the pass-band is described. Also, a theoretical method of determining the amplitude probability distribution of the filter output is described. The equations derived are solved for the case of third-order filters. Experimental and theoretical characteristics are given for the case of a noise generator using a third-order filter.

Digital Simulation of Guidance and Control for Exo-Atmospheric Intercept

A mathematical model for various configurations of interceptor missiles operating outside the earth's atmosphere is described. The associated digital computer simulation program provides means for evaluating the performance of different guidance and control systems and for studying the influence of parameter variations on the overall mission effectiveness. The simulation program also provides a means for establishing dynamic and kinematic criteria for the variable mass interceptor configurations. A complete attack mission, from exo-atmospheric launch to kill, may be carried out in three-dimensional space with all six degrees-of-freedom of the interceptor accounted for in the dynamics. Several models of thrusting and passive tracking may be selected for guidance. The guidance law is based on biased proportional navigation. The program simulates the sensing of the target, control system functions, and interceptor dynamics, all in closed loop form. The control loops contain optional time lags, gains, limits, and shaping neetworks in addition to a White Gaussian noise generator capable of simulating both receiver noise and angular scintillation. The vehicle's physical characteristics, the control constants, and the intercept mission are entirely arbitrary. The target is a pre-programmed point mass whose trajectory may be described by tabular data, equations for constant acceleration, circular equations, or other options. Output generated consists of time histories of all significant functions and a series of plots generated on a 1403 printer. A simple mission used to demonstrate the capabilities of the program will be discussed.

Acoustical Analysis of the Norwegian S-Sound

By analysis of the Norwegian s it was found that the spectrum at any rate contains frequencies up to 16 kc/s. It contains also a series of resonance frequencies. The average number for the most distinctive ones is 4. The peaks are, on the whole, evenly distributed. It seems as though some persons pronounce s with more fixed resonances than others.The spectra of s are compared with different sound combinations. The distribution of the maximum was investigated, but no change was proved. There is a tendency for the maximum to be moved towards lower frequencies for s as initial sound.It seems as though women pronounce s with greater intensity, in the higher frequency range, than men. It is impossible to prove any difference owing to age or dialect.It is shown that the spectrum changes with the duration of s. It seems as though the maximum is moved towards lower frequencies.With the aid of a white-noise generator and a filter, a synthetic s was produced. One finds that this must contain at least one pure tone ...

Design and Development of a Standard White Noise Generator and Noise Indicating Instrument

Design and Development of a Standard White Noise Generator and Noise Indicating Instrument