Wide-band White Noise Research Articles

An integrated analog/digital random noise source

An integrated noise source (INS) has been fabricated in a standard 1.2 /spl mu/m digital CMOS technology. Wideband white noise is generated from the amplified thermal noise of large resistors, which in turn is coupled into a comparator to generate a random digital bit stream. The INS generates 100 mV rms of analog output noise over a bandwidth of 3.2 MHz and operates from a single 5 V power supply with a quiescent current of 7.4 mA. The circuit has an area of 2.92 mm/sup 2/. Potential applications of the INS include data encryption, mathematical simulation, and circuit test and measurement.

Experimental measurements of vibrational energy and acoustic radiation for a 3-D truss

The MIT Structural Acoustics Group is making experimental measurements to determine the structural loss and radiation efficiency of an undamped, three-dimensional truss structure, constructed of 0.5-in. aluminum tubing connected by massive aluminum joints. The truss was excited with a shaker driven by wideband white noise out to 20 kHz. The total vibrational energy in the truss was calculated by spatially integrating the energy estimated from acceleration measurements made over the entire truss. This value and the total input power, as measured with an impedance head, allow estimation of the total loss factor for the truss as a function of frequency. Total radiated sound power was calculated by spatially integrating a set of average acoustic intensity measurements made over a grid surrounding the truss. Since the total radiated sound power is known, the total loss factor can easily be broken down into a structural loss factor and a radiation loss factor. These measurements show that the radiation loss is smaller than structural loss, but larger than radiation from an equivalent length single strut would predict. The additional radiation is accounted for by a factor due to multipath in the truss. This factor is frequency dependent and can be estimated from the data by comparing to theory. [Research supported by ARPA and ONR.]

Characterization of prediction in the primate visual smooth pursuit system

To define predictive behavior and mechanisms in visual smooth pursuit, various target motions were presented to 2 monkeys. Target stimuli included: single sinusoids (1′s), triangle waves (T's), sums of 4 nonharmonically related sinusoids (4′s), bandpass limited white noise (B's), and wideband white noise (N′s). Velocity error was least for 1′s, greatest for N′s, and intermediate for T's, 4′s, and B's. For the bandlimited 4′s and B's, monkeys demonstrated the greatest relative amplitude response at the highest frequencies. Predictive mechanisms are classified as short- and long-term, depending on how much past target motion information is employed. The T's and a modification of this stimulus pattern involving a random perturbation were used to test the hypothesis that prediction is based exclusively on short-term signal processing related to target position and its derivatives. The existence of long-term predictive mechanisms in monkey smooth pursuit was unequivocally demonstrated with the use of the latter stimulus.

Errors in frequency parameters of EMG power spectra

Frequency shifts in random signals, e.g., EMG or Doppler ultrasound, can be followed by monitoring one or more parameters of the power spectrum. When such a frequency parameter is determined over a finite length of the signal, a random error and sometimes a systematic error or bias are introduced. Approximate expressions, in terms of moments of the power spectrum, have been derived for bias and standard deviation of the estimates for mean frequency, zero-crossing frequency, and fractile frequency (of which the median frequency is a special case). Experimental results from surface EMG recordings of three human muscles in constant force isometric contractions were in agreement with the theoretical predictions. In this case the mean frequency had the smallest random error. It turned out that the measured values of the zero-crossing frequency can deviate considerably from the predictions by the Rice formula when the amplitude distribution is not exactly Gaussian. In the presence of noise, all frequency parameters show a systematic deviation, depending on the signal-to-noise ratio. In addition to known results on this deviation for mean and zero-crossing frequency, an exact and an approximate expression for the fractile frequency are given. In the case of EMG plus wide-band white noise, the median frequency has the best immunity to noise.

A new quantitative indicator of visual fatigue.

Ocular-motor correlates of visual fatigue have remained elusive. Performance of ocular-motor tracking with a wide-band white noise input and the response of the dual-mode, smooth pursuit-saccadic eye movement system as output was used to test visual fatigue. A new visual fatigue indicator, VFI, was defined as the nonlinear remnant after subtracting an identified impulse response contribution to the output. Subjects were required to perform very fatiguing CRT screen reading tasks, and the VFI correlated well with the subjective reports of visual fatigue.

Response durations and false alarm reaction times

Three Long-Evans rats were initially trained to depress and hold down a response lever in the presence wideband white noise pulsing at 6.7 Hz for a variable period between 4 and 6 s to obtain a 45-mg food pellet. This reinforcement schedule is the same as operating a one-lever press-release psychophysical procedure with a variable foreperiod of 2–4 s and a 2-s trial duration with only no-signal trials. The initial training of the nonsignal trial correct response of holding the lever down throughout the trial permits the measurement of the temporal characteristics of the background level of release responses in the absence of a history of contingent reinforcement for releasing the lever. After training to asymtotic performance on the nonsignal trials alone, 50% signal trials (where the noise. pulsation rate changed to 12.5 Hz) were included. Discrimination training was followed by changes in response duration histograms and false alarm reaction time histograms. In two of the three rats, there was an increase in the probability of incorrect lever releases 3–6 s after the lever was depressed. [Work supported by NIEHS grant RO1ES02750 to R. M. Lebovitz.]

Error analysis in sampling theory : A. Papoulis, Proc. IEEE54, No. 7, July (1966), p. 947

It is well known that an elastic column subjected to a harmonically-varying axial force exhibits parametric resonance over a range of applied frequencies and amplitudes. In this paper, the effect of white noise on the dynamic stability properties of a model system is investigated. Because of the complex nature of the applied loads and the nonlinearity of the governing equilibrium equation, three different numerical integration procedures are considered for determining the response of the model structure, and the accuracy of each scheme is studied. Results from the numerical investigation show that the method of Successive Symmetric Quadratures provides greater accuracy than the conventional Newmark Method or Harmonic Acceleration Method for nonlinear dynamic systems under random excitation. Computation of the model response shows that band-limited low frequency noise can limit the maximum deformation of the model system relative to the unperturbed case. Wide-band white noise, however, was observed only to enhance the destabilizing effect of the applied loads.

Audio analgesia. A new problem for otologists.

Audio refers to the use of sound to allay pain. This method has been used particularly in dentistry and, on a more limited scale, in obstetrics, but it may find further and more general application. Apparatus to produce the necessary loud sound, usually stereophonic music or wideband white noise delivered to the patient through earphones, with the volume under the control of the patient, has been developed and placed on the market. The use of these instruments poses a new problem for otology because the effectiveness of the loud sound in distracting and relaxing the patient or otherwise producing the analgesia depends at least in part on the high level at which the noise is delivered. The levels are such that permanent threshold shifts would be expected if persons were habitually exposed to them for several hours a day. Fortunately, the human ear can tolerate the necessary intensities of