Digital Spectral Analysis Research Articles

Performance evaluation of cascaded rectangular windows in spectral analysis

This paper describes a novel approach to the evaluation of the errors associated with the sampling strategy and the windowing process in digital spectral analysis. The proposed procedure, which is based on the introduction of a general expression for the estimation of input signal spectral components capable of separately pointing out the different sources of error, has been applied to the cascade of any number of rectangular windows in presence of periodic sampling. In addition, the approach has been further developed by assuming that the initial sampling time instant could be randomized, so that each spectral component estimated can be considered as a random variable, described through the classic statistical parameters. These parameters quantify the uncertainty associated with the windowing process considered and the sampling scheme adopted. In this paper, they have been theoretically deduced in a closed form in the case of a cascade of two and three rectangular windows respectively, along with a generalisation to the cascade of any number of elements, and compared with those of the single window in terms of the specific errors due to the sampling and windowing (i.e. resolution, leakage and aliasing). In particular, it has been shown that the cascaded technique can carry out a substantial reduction of the uncertainty associated with the input signal harmonic estimates. The comparison between theoretical findings and simulations is provided, showing a very good agreement.

Developmental aspects of infant’s cry melody and formants

This paper deals with the analysis of cry melodies (time variations of the fundamental frequency) as well as vocal tract resonance frequencies (formants) from infant cry signals. The increase of complexity of cry melodies is a good indicator for neuro-muscular maturation as well as for the evaluation of pre-speech development. The variation of formant frequencies allows an estimation of articulatory activity during pre-speech vocalization. Subjects are three pairs of healthy identical twins (monocygozity determined by DNA-fingerprint). Spontaneous cries of these six children were recorded at different ages: 8th–9th week, 15th–17th week and 23rd–24th week. Analysis of 136 cry melodies and intensity contours was made using KAY-CSL 4300/MDVP. For formant estimation a spectral parametric technique was applied, which was based on autoregressive models (Digital spectral analysis with applications, 1987) whose order is adaptively estimated on subsequent signal frames by means of a new method (Med. Eng. Phys. 20 (1998) 432; Utras. Med. Biol. 21 (1995) 793). Cry melodies exhibited an increasing complexity during the observation period. Beginning with the second observation period (15th–17th week) an increasing coupling and tuning between melody and resonance frequencies was observed, which was interpreted as “intentional” articulatory activity. Possible applications are in cry diagnosis as well as in the evaluation of pre-speech development.

Monitoring hemodialysis vascular access by digital phonoangiography.

We are intrigued by the possibility of using digital spectral analysis to detect hemodialysis vascular access stenosis. Such a monitor could be inexpensive, noninvasive, and portable enough to allow continuous monitoring. This report suggests how individuals wishing to conduct such research can use a simple but effective transducer design we have employed, how the data so obtained can be analyzed in the time and frequency domains using inexpensive digital signal processing software available via the Internet, and how data recordings might be shared via the Internet to facilitate collaboration.

Low-frequency waves of inflation and economic growth: Digital spectral analysis

Modern digital spectral analysis confirms that very noisy inflation and economic growth series share ∼9- and ∼18-year business and building cycle signals, but that inflation alone displays the additional ∼28- and ∼56-year rhythms of the long wave. The growth cycle that accounts for the greatest variance is one of ∼6 years, probably associated with El Niño-Southern Oscillation (ENSO) fluctuations. Discussion of these results leads to clarification of major sources of confusion in the long-wave literature, and to confirmation of the hypothesis that mode-locked endogenous rhythms may have their timing controlled by an exogenous pacemaker that links inflation and growth.

Broadband ultrasonics applied to phase transition characterisation in chromium antiferromagnetic alloy

LABOEND/PEMM/EE/COPPE, Federal University of Rio de Janeiro, P.O.Box 68505, CEP 21945-970 Rio de Janeiro-RJ, Brazil(Received October 4, 2000)(Accepted in revised form January 17, 2001)Keywords: Acoustic methods; Phase transformations; Nondestructive testing; Magnetic structureIntroductionUltrasonic pulse-echo techniques are being widely used in the investigation of magnetic phasetransitions in solid materials [1,2]. In general, changes in the ultrasonic pulse amplitude and velocity aremeasured, and then the ultrasonic attenuation and elastic constants are determined for fixed frequenciesgiven by the odd harmonics of the transducer coupled to the sample. It is difficult to reproduce the sameconditions of coupling between transducer and sample, therefore most analyses are limited to a fewfixed frequencies. An investigation of the ultrasonic pulse propagation close to a magnetic phasetransformation, for a continuous frequency range, is presented using wide band transducers and digitalspectral analysis. The material chosen is a single crystal of Cr-0.18at%Re, which has a magnetic phasetransformation from the paramagnetic (PM) to an antiferromagnetic (AFM) state at 318 K [3,4].Similarly to pure chromium, the ultrasonic attenuation and internal friction for this alloy have acontribution due to the coupling between the spin density wave in the AFM phase and the oscillatoryelastic strain introduced by the ultrasonic pulse. Since the sixties the ultrasonic broadband analysis isbeing widely used for many applications [5–8]. In this paper, we have shown that the ultrasonic spectralanalysis approach is highly advantageous in many aspects for the investigation of phase transitions.Experimental MethodThe Cr-0.18at%Re single crystal used was obtained from a larger ingot previously investigated byneutron scattering [9] and cut with faces parallel to the crystallographic directions [001], [110] and[110] with dimensions of 10 3 12 3 6 mm. The full half width at half maximum (FWHM) of the Braggpeak was found to be less than 0.5° after standard procedure of electropolishing with oxalic acid.The measurement was performed using the immersion in water technique with a broadbandKrautkra¨mer transducer model IAP 50.2.1, which has a good response in the frequency interval from5 MHz to 40 MHz. The generator/receptor excites the transducer with a wide band pulse, and thegenerated ultrasonic pulse propagates through the water/sample system. Part of the pulse reflects at

Effect of Ionospheric Plasma Irregularities on Communication System Parameters

The scintillation has been monitored at Rajkot using the VHF (250 MHz) signals from geostationary satellite FLEETSAT at 73°E since 1986. The paper describes the observed characteristics of scintillation such as its noctural occurrence pattern, seasonal, geomagnetic and solar activity dependence. Employing digital data acquisition and power spectral analysis techniques, quantitative parameters such as the scintillation index S4, upper roll of frequency and spectral slope are derived and discussed in terms of the parameters of causative plasma irregularities. Spaced receiver technique and cross correlation analysis is employed to determined the characteristic scale size and velocity of the irregularities. A comprehensive study of the above parameters throws some light on the possible plasma instability mechanism responsible for the generation of those irregularities. The effects of the irregularities in terms of signal statistics such as cumulative amplitude distribution functions, fade rate, message reliability and bit error on a typical modern communication system are computed and presented.

Fertility cycles: a note on onset and periodicity.

The fertility transition was completed in Concord, Mass., by the end of the War of 1812. Thereafter, there has been baby boom-baby bust cyclically, a rhythm clearly demonstrated by the use of modern methods of digital spectral analysis.

The Duality of Leakage and Aliasing and Improved Digital Spectral Analysis Techniques

When processing, recording, and analyzing continuous, analog signals or functions with a digital computer, information is lost when the signals are converted to digital form. When signals are sampled in one domain (time or frequency), the loss of information is characterized as aliasing in the other (frequency or time, respectively) domain. When a signal or function is truncated in one domain, the information loss is characterized as leakage in the other domain. It is shown that because of the dual nature of leakage and aliasing, that leakage in one domain reduces aliasing in the other domain and visa-versa. Examples of reducing leakage or aliasing in each domain by the dual in the other domain are given to illustrate. Since current art has not used time aliasing to reduce frequency leakage previously, a time alias processor for this purpose is described. A flat-top window function with spectral one frequency line in width is used in conjunction with the time alias processor to maintain leakage to within the nearest frequency line.

A method of digital spectral analysis of hydroacoustic signals

A sequence of operations for the spectral and correlation estimation of digitized random signals is suggested using a fast Fourier transform. A set of algorithms and their possible modifications, which can be used in developing the spectral estimation programmes aimed at operative derivation of processing data is represented in compressed information form.

In situ monitoring of object beam expander noise in speckle correlation interferometry

Expanded beams used for object illumination in industrial speckle correlation interferometry are susceptible to noise arising from dirt particles and defects found in the beam expanders. This results in a degeneration of the fringe information. To ensure the integrity of this information, an objective means of monitoring in situ the extent of expander noise is required. In this paper, a practical and cost-effective method based on digital spectral analysis is proposed and demonstrated.

The effect of subionospheric propagation on whistlers as deduced from direction finding measurements

The characteristics of subionospheric propagation of magnetospheric whistlers have been investigated by means of both digital spectral analysis with high resolution and our field‐analysis direction finding measurement for whistlers observed in South China. It is found that very low latitude whistlers, propagated in the Earth‐ionosphere waveguide over a distance of the order of 1000km, exhibit very clear additional dispersion effects near the cutoff frequencies of the subionospheric 1st‐ and higher‐order modes. The additional traces are also found to be left‐handed polarized, and when the frequency approaches the cutoff frequencies, the wave polarization becomes very close to exactly left‐handed circular and the incident angle becomes nearly vertical. While, the whistler components at frequencies away from the cutoff frequencies are linearly polarized. Finally, we emphasize the important use of the subionospheric propagation characteristics in the study of the whistler duct structure, ionospheric transmission of a downgoing whistler and its excitation of subionospheric modes.

Resolved conformational states of spin-labeled calcium-ATPase during the enzymic cycle

We have used frequency- and time-resolved electron paramagnetic resonance (EPR) to study the effects of substrate on the nanosecond conformational dynamics of the Ca-ATPase of sarcoplasmic reticulum, as detected by an iodoacetamide spin label (IASL) attached covalently to the enzyme. We confirm previous results [Coan, C. (1983) Biochemistry 22, 5826] showing that this probe is less rotationally mobile following the addition of nucleotides (ADP, AMPPNP, ATP) and that the shape of the spectrum suggests the presence of two components. We used two approaches to enhance EPR resolution in order to resolve the spectral components and their corresponding conformational states. First, to improve resolution in the frequency (spectral) domain, we used perdeuterated IASL, which results in narrower line widths. Digital spectral analysis resolves the EPR spectrum into two components, one that is indistinguishable from the spectrum observed in the absence of ligands and another that indicates more restricted probe motions, suggesting a distinct conformation of the labeled protein. Additions of substrate ligands appear to change only the mole fractions of the two components. The mole fraction of the restricted component (fR) was 0 in the absence of ligands, but increased to about 0.5 in the presence of saturating concentrations of AMPPNP and Ca2+. In general, ATP and its analogs increase fR, with larger effects observed in the presence of Ca. However, calcium has no effect by itself (fR = 0). Both monovanadate and decavanadate increase fR, but the formation of a covalent phosphoenzyme from inorganic phosphate (E2-P) had no effect (fR = 0).(ABSTRACT TRUNCATED AT 250 WORDS)

The measurement of through thickness plate vibration using a pulsed ultrasonic transducer : Journal of the acoustical society of America, vol. 83, no. 2, pp. 623–631 (Feb. 1988)

The use of pulsed ultrasound and digital spectral analysis to measure the through thickness vibration characteristics of plates has been investigated. It has been shown that, even at nominally normal incidence, some shear modes of the plate are excited in addition to the longitudinal modes. By modeling the propagation of an ultrasonic pulse through the plate, it has been shown that this is due to the mode conversion of the edge waves from the probe, which are always at a nonzero angle of incidence to the structure. However, not all the shear modes of the plate are excited in this way, and both the pulse propagation model described here and classical analyses can be used to predict correctly which shear modes will be observed. The results show that the use of pulse excitation and digital spectral analysis can give very accurate results and, since the testing time required is small, the technique is much more attractive for use in nondestructive testing than the conventional methods employing sine wave excitation.

Linear and circular digital spectral analysis of serial data

Two methods of digital spectral analysis of unevenly sampled data are developed and illustrated here. One method uses a linear function of time (or space), the other uses circular functions. The circular method turns out to be essentially equivalent to a least-squares sine-wave analysis. The linear, anharmonic method uses only the field of real numbers and elementary algebraic operations, and hence it can be made computationally very fast and accurate. Both methods are very general, properly handling all kinds of time series ranging from simple series consisting only of the times of events to complicated series consisting of pulses with long duty cycles. The two methods are here applied to the analysis of annual mean relative sunspot numbers.

Digital Spectral Analysis with Applications

First Page

Experimental measurement of three-wave coupling and energy cascading

The nonlinear coupling coefficient and the energy transfer associated with three-wave interactions are computed from measured data of the turbulent edge plasma of the Texas Experimental Tokamak(TEXT) [Nucl. Technol. Fusion 1, 479 (1981)]. The results show the presence of three-wave interactions. The interactions cause energy to cascade away from the dominant waves of the spectrum primarily toward lower, but also toward higher frequencies. The results are obtained with a new digital spectral analysis technique based on the estimation of higher-order cumulants. The method is discussed and tested on a simulation experiment. The same technique is useful for neutral fluids as well.

Nonlinear spectral dynamics of a transitioning flow

The nonlinear spectral dynamics of a transitioning flow in the wake of a flat plate is experimentally studied at different downstream positions with a two-point method. The measurement setup consists of two sensors, which are separated in the downstream direction. The quadratically nonlinear transfer function between the two points is then estimated from the digitized fluctuation data. Such transfer functions permit one to quantify the quadratically nonlinear spectral dynamics occurring between the two sensor points. The method used to estimate the transfer functions and local bicoherency for non-Gaussian input and output signals, by means of digital spectral analysis techniques, is briefly discussed. The measured quadratic transfer function of the experimental data changes gradually with downstream distance, but its main features are unchanged. The observed appearance of progressively higher harmonics of the fundamental mode and the filling in of the spectral valleys over short downstream distances are, thus, mainly caused by spectral redistribution of energy that is available in the interacting modes and not caused by abrupt changes in the coupling properties. This result is supported by the local bicoherency measurements.

A comparison of alternative procedures for digital spectral analysis of speech

Researchers now enjoy an increasingly wide selection of alternative procedures with which to characterize the time × frequency × amplitude variation in a speech waveform. Spectral analyses using a filter‐bank technique, the digital Fourier transform (DFT), and a variety of linear predictive coding (LPC) procedures are now widely available. Approaches using an autoregressive (AR), moving average (MA), auto‐regressive moving average (ARMA), or maximum entropy (ME) procedure are already widely available, or are becoming available. The present paper reviews the assumptions of, and the interrelations between, alternative methods, and outlines the relative advantages of the various approaches in providing information about the speech waveform. Finally, the human factors aspects of alternative spectral displays are discussed.

Method and apparatus for speech recognition and reproduction

Speech signal analysis for data reduction, as stored for synthesis or recognition, is improved by features including: digital spectral analysis; reduction of channel data and bit allocation by selective summation of groups of contiguous data; using the mean average of the log amplitude to find the deviation for each channel; also using the instaneous shape of the mean value for each channel for pairs of adjacent frames, all combined to find a feature ensemble for each pair of adjacent frames.

Advanced plasma fluctuation analysis techniques and their impact on fusion research (invited)

This article reviews digital spectral analysis techniques that yield experimental insight into plasma turbulence. Methods to quantify the statistical properties of the fluctuations and to measure the particle and heat flux caused by electrostatic fluctuations are presented. Furthermore, analysis techniques to study the nonlinear coupling process of turbulence and the redistribution of energy among the different modes are discussed. The impact of the analysis techniques on fusion research is demonstrated with experimental results collected with Langmuir probes, heavy-ion beam probes, and laser scattering in the tokamak TEXT. Special emphasis is given to the characterization of the wavenumber distribution and the correlation lengths in all toroidal directions, including a first measurement of k∥ in a tokamak.