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Proceedings of the IEEE

Issue 9 • Date Sept. 1996

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Displaying Results 1 - 14 of 14
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  • Preface to the Special Issue on Time-Frequency Analysis

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    Freely Available from IEEE
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  • Applications of time-frequency analysis to signals from manufacturing and machine monitoring sensors

    Page(s): 1319 - 1329
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    Manufacturing industries are now demanding substantial increases in flexibility, productivity and reliability from their process machines as well as increased quality and value of their products. One important strategy to support this goal is sensor-based, on-line, real-time evaluation of key characteristics of both machines and products, throughout the manufacturing process. Recent advances in time-frequency (TF) analysis are particularly well suited to extracting key vibrational characteristics from monitoring sensors. Thus this paper presents applications of TF analysis to several important manufacturing and machine monitoring tasks, to show the value of these forms of digital signal processing applied to manufacturing View full abstract»

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  • Time-frequency analysis of musical signals

    Page(s): 1216 - 1230
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    The major time and frequency analysis methods that have been applied to music processing are traced and application areas described. Techniques are examined in the context of Cohen's class, facilitating comparison and the design of new approaches. A trumpet example illustrates most techniques. The impact of different analysis methods on pitch and timbre examination is shown. Analyses spanning Fourier series and transform, pitch synchronous analysis, heterodyne filter, short-time Fourier transform (STFT), phase vocoder, constant-Q and wavelet transforms, the Wigner (1932) distribution, and the modal distribution are all covered. The limitations of windowing methods and their reliance on steady-state assumptions and infinite duration sinusoids to define frequency and amplitude are detailed. The Wigner distribution, in contrast, uses the analytic signal to define instantaneous frequency and power parameters. The modal distribution is shown to be a linear transformation of the Wigner distribution optimized for estimating those parameters for a musical signal model. Application areas consider analysis, resynthesis, transcription, and visualization. The more stringent requirements for time-frequency (TF) distributions in these applications are compared with the weaker requirements found in speech analysis and highlight the need for further theoretical research View full abstract»

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  • The application of time-frequency methods to the analysis of postural sway

    Page(s): 1312 - 1318
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    We apply time-frequency (TF) spectral analysis techniques, namely evolutionary spectral estimators, to postural sway data gathered during quiet standing and in response to external visual stimuli. These techniques provide insight into the time-varying properties of the human balance control systems during standing. We demonstrate by means of individual and group examples that the results of the TF methods can be used to characterize the behavior of the balance system for groups of patients and controls. Specifically we show that, for healthy control subjects, sway at a visual stimulus frequency toward and away from the subject shows an amplitude which decays in time. On the other hand, patients display a response whose amplitude at the stimulus frequency increases with time. Thus TF analysis yields insights into the time-varying nature of the postural control system View full abstract»

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  • Monitoring neuronal oscillations and signal transmission between cortical regions using time-frequency analysis of electroencephalographic activity

    Page(s): 1295 - 1301
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    Oscillatory states in the electroencephalogram (EEG) reflect the rhythmic synchronous activity in large networks of neurons. Time-frequency (TF) methods, which quantify the spectral content of the EEG as a function of time, are well suited as tools for the study of spontaneous and induced changes in oscillatory states. The use of these methods provides insights into the temporal dynamics of EEG activity in both humans and experimental animals, and aids the study of the neuronal mechanisms that generate rhythmic EEG activity. Further the use of TF coherence analysts, which quantifies the consistency of phase relationships in multichannel EEG recordings, may contribute to the understanding of signal transmission between neuronal populations in different parts of the brain. We have used TF techniques to analyze the flow of activity patterns between two strongly connected brain structures: the entorhinal cortex and the hippocampus. Both of these structures are believed to be involved in information storage. By applying various frequencies of stimulation, we have found a peak in the spectral power in both sites at around 18 Hz, but the coherence between the EEG signals recorded from these sites was found to increase monotonically up to about 35 Hz. We have also found that long-term potentiation, a strong increase in the efficacy of excitatory synapses between these sites, either had no effect or decreased coherence View full abstract»

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  • The application of two-dimensional signal transformations to the analysis and synthesis of structural excitations observed in acoustical scattering

    Page(s): 1249 - 1263
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    Acoustic scattering from air-filled, elastic shells submerged in water is an important problem in applied science. The excitations of interest yield a set of physically distinct components to the impulse response of a shell. The components form a natural basis for all signals which can be observed in acoustical scattering experiments from the shell via temporal convolution with some chosen input signal. The Fourier transform (FT) of the impulse response of a shell yields its transfer function, which is also called the form function. We study two types of shells in this paper: a spherical shell, and a finite, ribbed, cylindrical shell with endcaps. Utilizing several different two-dimensional (2-D) signal transformations, we can decompose the response of the shells. The resulting 2-D images allow for a striking visual decomposition of the responses into their distinct components. In the case of the spherical shell, a virtually exact theory exists that allows for analytic synthesis of the shell response into its components. However, for the more complex cylindrical shell, the theory for the direct scattering problem is not nearly so mature. Yet, we can still decompose experimentally-obtained shell responses into their distinct components via signal synthesis techniques applied to the 2-D transforms View full abstract»

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  • Time-frequency analysis of skeletal muscle and cardiac vibrations

    Page(s): 1281 - 1294
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    Skeletal muscle and the heart vibrate during contraction producing nonstationary signals whose time-varying frequency reflects dynamic changes in physiological properties. Consequently, pathological changes in the mechanical integrity or loading of skeletal muscle or the heart can be expected to alter their vibrations. Classic frequency analysis techniques have been inadequate to characterize these subtle changes because of rapidly varying frequency components. A poor understanding of heart and muscle sound generation has also limited investigations. This paper demonstrates how time-frequency (TF) techniques have illuminated the relationships between muscle/heart material properties and loading and frequency dynamics of heart and muscle vibrations. Studies of evoked twitches from frog skeletal muscle reveal that muscle vibrations occur as transverse oscillations at the muscle's resonant frequency. Using a classic Rayleigh-Ritz model and crude estimates of the muscle geometry, muscle force can be accurately predicted from the muscle sound TF profile. First heart sound vibrations, in contrast, are shown to be a nonresonant phenomena, consisting of propagating transients superimposed upon bulk acceleration of myocardial contraction. Consequently, first heart sound frequency dynamics depend upon cardiac electrical excitation and hemodynamic loading in addition to intrinsic material properties and geometry, necessitating further work to characterize pathophysiologic correlations View full abstract»

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  • Mechanical signature analysis using time-frequency signal processing: application to internal combustion engine knock detection

    Page(s): 1330 - 1343
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    Signature analysis consists of the extraction of information from measured signal patterns. The work presented in this paper illustrates the use of time-frequency (TF) analysis methods for the purpose of mechanical signature analysis. Mechanical signature analysis is a mature and developed field; however, TF analysis methods are relatively new to the field of mechanical signal processing, having mostly been developed in the present decade, and have not yet been applied to their full potential in this field of engineering applications. Some of the ongoing efforts are briefly reviewed in this paper. One important application of TF mechanical signature analysis is the diagnosis of faults in mechanical systems. In this paper we illustrate how the use of joint TF signal representations can result in tangible benefits when analyzing signatures generated by transient phenomena in mechanical systems, such as might be caused by faults or otherwise abnormal operation. This paper also explores signal detection concepts in the joint TF domain and presents their application to the detection of internal combustion engine knock View full abstract»

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  • Time-frequency analysis and auditory modeling for automatic recognition of speech

    Page(s): 1199 - 1215
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    Modern speech processing research may be categorized into three broad areas: statistical, physiological, and perceptual. Statistical research investigates the nature of the variability of the speech waveform from a signal processing viewpoint. This approach relates to the processing of speech in order to obtain measurements of speech characteristics which demonstrate manageable variabilities across a wide range of the talker population, in the presence of noise or competing speakers as well as the interaction of speech with the channel through which it is transmitted, and under the inherent interaction of the information content of speech itself (i.e., the contextual factor). Physiological research aims at constructing accurate models of the articulatory and auditory process, helping to limit the signal space for speech processing. In the perceptual realm, work focuses on understanding the psychoacoustic and possibly the psycholinguistic aspects of the speech communication process that the human so conveniently conducts. By studying this working analysis/recognition system, insights may be garnered that will lead to improved methods of speech processing. Conversely by studying the limitations of this system, particularly how it reduces the information rate of the received signal through, for example, masking and adaptation improvements may be made in the efficiency of speech coding schemes without impacting the quality of the reconstructed speech. Thus comprehension of speech production and perception impacts methods of speech processing, and vice-versa. This paper enunciates such a position, focusing on how modern time-frequency signal analysis methods could help expedite needed advances in these areas View full abstract»

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  • Signal analysis by means of time-frequency (Wigner-type) distributions-applications to sonar and radar echoes

    Page(s): 1231 - 1248
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    Time series data have been traditionally analyzed in either the time or the frequency domains. For signals with a time-varying frequency content, the combined time-frequency (TF) representations, based on the Cohen class of (generalized) Wigner distributions (WD's) offer a powerful analysis tool. Using them, it is possible to: (1) trace the time-evolution of the resonance features usually present in a standard sonar cross section (SCS), or in a radar cross section (RCS) and (2) extract target information that may be difficult to even notice in an ordinary SCS or RCS. After a brief review of the fundamental properties of the WD, we discuss ways to reduce or suppress the cross term interference that appears in the WD of multicomponent systems. These points are illustrated with a variety of three-dimensional (3-D) plots of Wigner and pseudo-Wigner distributions (PWD). The plots are all obtained from an extensive analysis we have made over the years of the resonance acoustic echoes backscattered by a variety of elastic shells submerged in water, when they are excited by various types of incident pressure waves, including the short pulses generated by explosive charges. We also review studies we have made of the echoes returned by conducting or dielectric targets in the atmosphere, when they are illuminated by broadband radar pings. These short incident pulses are used to analytically model the performance of ultrawide band (UWB) radars, often called impulse radars. A TF domain analysis of these impulse radar returns demonstrates their superior information content View full abstract»

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  • Localizing functional activity in the brain through time-frequency analysis and synthesis of the EEG

    Page(s): 1302 - 1311
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    Multichannel electroencephalograms (EEGs) are processed using time-frequency (TF) analysis and synthesis techniques to geometrically localize neuroelectric generators of specific activity contained within the observed EEG. The TF domain techniques are utilized to separate the signals of interest from the remainder of the EEG, by allowing the definition of regions of interest which contain the signals for which we desire to localize the underlying neuronal generators. This approach essentially introduces a filtering technique which allows the distortionless separation of the signals of interest from all other components recorded. The source of the functional activity in the brain is estimated and mapped numerically by a least-squares approach. We have applied these techniques to identify the anatomical location of the sleep spindle, a component of the EEG observed during sleep, which is of importance in understanding the generation of sleep and sleep patterns View full abstract»

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  • Reduced interference distributions: biological applications and interpretations

    Page(s): 1264 - 1280
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    Time-frequency (TF) signal analysis has recently experienced a slow awakening followed by an accelerating development of interest. This paper discusses a specific concept applied to TF signal analysis, the reduced interference distribution (RID) approach. The RID approach is aimed at achieving high-resolution TF distributions within Cohen's class with much reduced cross term or interference activity which often disappoints users of the well-known Wigner distribution (WD). The RID concept is briefly developed and then a number of examples from biomedical and biological settings are discussed. These discussions attempt to accomplish the dual task of illustrating the usefulness of the approach in investigating these problems and to teach one how to interpret the results obtained as well-the art of using the approach. RID results are contrasted with the WD and the spectrogram, another well-known tool. Some of the new and exciting TF approaches that deviate from the RID concept, but provide good results and interesting theoretical frameworks, are also brought in as appropriate View full abstract»

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