• 제목, 요약, 키워드: Time-frequency

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On Improving Resolution of Time-Frequency Representation of Speech Signals Based on Frequency Modulation Type Kernel (FM변조된 형태의 Kernel을 사용한 음성신호의 시간-주파수 표현 해상도 향상에 관한 연구)

  • Lee, He-Young;Choi, Seung-Ho
    • Speech Sciences
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    • v.12 no.4
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    • pp.17-29
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    • 2005
  • Time-frequency representation reveals some useful information about instantaneous frequency, instantaneous bandwidth and boundary of each AM-FM component of a speech signal. In many cases, the instantaneous frequency of each component is not constant. The variability of instantaneous frequency causes degradation of resolution in time-frequency representation. This paper presents a method of adaptively adjusting the transform kernel for preventing degradation of resolution due to time-varying instantaneous frequency. The transform kernel is the form of frequency modulated function. The modulation function in the transform kernel is determined by the estimate of instantaneous frequency which is approximated by first order polynomial at each time instance. Also, the window function is modulated by the estimated instantaneous. frequency for mitigation of fringing. effect. In the proposed method, not only the transform kernel but also the shape and the length of. the window function are adaptively adjusted by the instantaneous frequency of a speech signal.

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Adaptive Short-time Fourier Transform for Guided-wave Analysis (유도 초음파 신호 분석을 위한 적응 단시간 푸리에 변환)

  • Sun, Kyung-Ho;Hong, Jin-Chul;Kim, Yoon-Young
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.606-610
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    • 2004
  • Although time-frequency analysis is useful for dispersive wave analysis, conventional methods such as the short-time Fourier transform do not take the dispersion phenomenon into consideration in the tiling of the time-frequency domain. The objective of this paper is to develop an adaptive time-frequency analysis method whose time-frequency tiling is determined with the consideration of signal dispersion characteristics. To achieve the adaptive time-frequency tiling, each of time-frequency atoms is rotated in the time-frequency plane depending on the local wave dispersion. To carry out this adaptive time-frequency transform, dispersion characteristics hidden in a signal are first estimated by an iterative scheme. To examine the effectiveness of the proposed method, the flexural wave signals measured in a plate were analyzed.

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Adaptive Short-time Fourier Transform for Guided-wave Analysis (유도 초음파 신호 분석을 위한 적응 단시간 푸리에 변환)

  • Hong, Jin-Chul;Sun, Kyung-Ho;Kim, Yoon-Young
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.3
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    • pp.266-271
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    • 2005
  • Although time-frequency analysis is useful for dispersive wave analysis, conventional methods such as the short-time Fourier transform do not take the dispersion phenomenon into consideration in the tiling of the time-frequency domain. The objective of this paper is to develop an adaptive time-frequency analysis method whose time-frequency tiling is determined with the consideration of signal dispersion characteristics. To achieve the adaptive time-frequency tiling, each of time-frequency atoms is rotated in the time-frequency plane depending on the local wave dispersion. To carry out this adaptive time-frequency transform, dispersion characteristics hidden in a signal are first estimated by an iterative scheme. To examine the effectiveness of the present method, the flexural wave signals measured in a plate were analyzed.

Rectangular prism pressure coherence by modified Morlet continuous wavelet transform

  • Le, Thai-Hoa;Caracoglia, Luca
    • Wind and Structures
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    • v.20 no.5
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    • pp.661-682
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    • 2015
  • This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent "structures" of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent "events" and the "coherent structure" of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a "modified" complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

The Comparative Effect of Time-Frequency Distribution Function in a Time-Frequency Domain Reflectometry System (시간-주파수 영역 반사파 계측 시스템에서 다양한 시간-주파수 분포 함수의 영향 연구)

  • Kwak, Ki-Seok;Tok, Son-Choe;Tae, Sung-Yoon;Jin, Bae-Park;Jae, Won-Kho
    • Proceedings of the KIEE Conference
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    • pp.2149-2151
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    • 2004
  • The time-frequency domain reflectometry(TFDR) is well known to detect and locate a fault in a coaxial cable[3]. Traditional reflectometry methods have been achieved in either the time domain or frequency domain only. However, the time-frequency domain reflectometry utilizes time and frequency information of a reflected signal passed through a cable to detect and locate the fault. The purpose of this paper is to find appropriate time-frequency distribution function suitable for a TFDR system. Choosing the appropriate time-frequency distribution function implies one can detect the fault and estimate the location accurately. We consider and compare adequate time-frequency distribution function on the basis of experimental results.

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Estimation of Fault Location on a Transmission Line via Time-Frequency Domain Reflectometry (시간-주파수 반사파 계측 방법을 이용한 전송선로의 결함 위치 추정)

  • Choe TokSon;Kwak Ki-Seok;Yoon Tae Sung;Park Jin Bae
    • The Transactions of the Korean Institute of Electrical Engineers D
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    • v.54 no.9
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    • pp.521-530
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    • 2005
  • In this paper, a new high resolution reflectometry scheme, time-frequency domain reflectometry(TFDR), isproposed to detect and estimate a fault in a transmission line. Traditional reflectometry methodologies have been achieved either in the time domain or in the frequency domain only. However, the TFDR can jump over the performance limits of the traditional reflectometry methodologies because the acquired signal is analyzed in time and frequency domain simultaneously. In the TFDR, the new reference signal and the novel TFDR algorithm are proposed for analyzing the acquired signal in the time-frequency domain. Because the reference signal of Gaussian envelop chirp signal is localized in the time and frequency domain simultaneously, it is suitable to the analysis in the time-frequency domain. In the proposed TFDR algorithm, the time-frequency distribution function and the normalized time-frequency cross correlation function are used to detect and estimate a fault in a transmission line. That algorithm is verified for real-world coaxial cables which are typical transmission line with different types of faults by the TFDR system composed of real instruments. The performance of the TFDR methodology is compared with that o( the commercial time domain reflectomeoy(TDR) experiments, so that concludes the TFDR methodology can detect and estimate the fault with smaller error than TDR methodology.

Developed empirical model for simulation of time-varying frequency in earthquake ground motion

  • Yu, Ruifang;Yuan, Meiqiao;Yu, Yanxiang
    • Earthquakes and Structures
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    • v.8 no.6
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    • pp.1463-1480
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    • 2015
  • This research aims to develop an empirical model for simulation of time-varying frequency in earthquake ground motion so as to be used easily in engineering applications. Briefly, 10545 recordings of the Next Generation Attenuation (NGA) global database of accelerograms from shallow crustal earthquakes are selected and binned by magnitude, distance and site condition. Then the wavelet spectrum of each acceleration record is calculated by using one-dimensional continuous wavelet transform, and the frequencies corresponding to the maximum values of the wavelet spectrum at a series of sampling time, named predominant frequencies, are extracted to analyze the variation of frequency content of seismic ground motions in time. And the time-variation of the predominant frequencies of 178 magnitude-distance-site bins for different directions are obtained by calculating the mean square root of predominant frequencies within a bin. The exponential trigonometric function is then use to fit the data, which describes the predominant frequency of ground-motion as a function of time with model parameters given in tables for different magnitude, distance, site conditions and direction. Finally, a practical frequency-dependent amplitude envelope function is developed based on the time-varying frequency derived in this paper, which has clear statistical parameters and can emphasize the effect of low-frequency components on later seismic action. The results illustrate that the time-varying predominant frequency can preferably reflect the non-stationarity of the frequency content in earthquake ground motions and that empirical models given in this paper facilitates the simulation of ground motions.

Estimation of Fault Location on a Power Line using the Time-Frequency Domain Reflectometry (절연전선 결함 위치 추정에 대한 시간-주파수 영역 반사파 계측법의 적용)

  • Doo, Seung-Ho;Kwak, Ki-Seok;Park, Jin-Bae
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.57 no.2
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    • pp.268-275
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    • 2008
  • In this paper, we introduce a new method for detecting and estimating faults on a power line using the time-frequency domain reflectometry system. The system rests upon time-frequency signal analysis and uses a chirp signal which is multiplied by Gaussian envelope. The chirp signal is used as a reference signal, and we can get the reflected signal from a fault on a wire. To detect and estimate faults, we analyze the reflected signal by Wigner time-frequency distribution function and normalized time-frequency cross correlation function. In this paper we design an optimal reference signal for power line and implement a system for estimating fault distance on a power line with the TFDR implemented by PXI equipments. This approach is verified by some experiments with HIV 2.25mm power lines.

Detection and Estimation of a Faults on Coaxial Cable with TFDR Algorithm (Time Frequency Domain Reflectometry 기법을 이용한 Coaxial Cable에서의 결함 감지 및 추정)

  • Song, Eun-Seok;Shin, Yong-June;Choe, Tok-Son;Yook, Jong-Gwan;Park, Jin-Bae;Powers, Edward J.
    • The Journal of Advanced Navigation Technology
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    • v.7 no.1
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    • pp.38-50
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    • 2003
  • In this paper, a new high resolution reflectometry scheme, time-frequency domain reflectometry (TFDR), is proposed to detect and locate fault in wiring. Traditional reflectometry methods have been achieved in either the time domain or frequency domain only. However, time-frequency domain reflectometry utilizes time and frequency information of a transient signal to detect and locate the fault. The time-frequency domain reflectometry approach described in this paper is characterized by time-frequency reference signal design and post-processing of the reference and reflected signals to detect and locate the fault. Design of the reference signal in time-frequency domain reflectometry is based on the determination of the frequency bandwidth of the physical properties of cable under test. The detection and estimation of the fault on the time-frequency domain reflectometry relies on the time-frequency domain reflectometry is compared with commercial time domain reflectomtery (TDR) instrument. In these experiments provided in this paper, TFDR locates the fault with smaller error than TDR. Knowledge of time and frequency localized information for the reference and reflected signal gained via time-frequency analysis, allows one to detect the fault and estimate the location accurately.

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Dispersion-Based Continuous Wavelet Transform for the Analysis of Elastic Waves

  • Sun, Kyung-Ho;Hong, Jin-Chul;Kim, Yoon-Young
    • Journal of Mechanical Science and Technology
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    • v.20 no.12
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    • pp.2147-2158
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    • 2006
  • The continuous wavelet transform (CWT) has a frequency-adaptive time-frequency tiling property, which makes it popular for the analysis of dispersive elastic wave signals. However, because the time-frequency tiling of CWT is not signal-dependent, it still has some limitations in the analysis of elastic waves with spectral components that are dispersed rapidly in time. The objective of this paper is to introduce an advanced time-frequency analysis method, called the dispersion-based continuous wavelet transform (D-CWT) whose time-frequency tiling is adaptively varied according to the dispersion relation of the waves to be analyzed. In the D-CWT method, time-frequency tiling can have frequency-adaptive characteristics like CWT and adaptively rotate in the time-frequency plane depending on the local wave dispersion. Therefore, D-CWT provides higher time-frequency localization than the conventional CWT. In this work, D-CWT method is applied to the analysis of dispersive elastic waves measured in waveguide experiments and an efficient procedure to extract information on the dispersion relation hidden in a wave signal is presented. In addition, the ridge property of the present transform is investigated theoretically to show its effectiveness in analyzing highly time-varying signals. Numerical simulations and experimental results are presented to show the effectiveness of the present method.