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Time-varying filter modelling and time-frequency characterisation of non-stationary sound fields due to a moving source

Record type: Thesis (Doctoral)

This thesis deals with the problems of modelling, interpretation and estimation of `non-stationary' processes with particular reference to acoustic problems. A common assumption in the modelling and analysis of a random process is that the process is `stationary'. Such an assumption may be a satisfactory approximation in many instances, but there are situations in which the processes are obviously non-stationary. In particular many physical non-stationary processes exhibit a `frequency-modulated' structure. An important example of such processes is the sound perceived by an observer due to a moving source emitting a random signal. In the thesis two methods are studied for the characterisation of such non-stationary processes; i) `time-frequency' spectral characterisation and ii) time-varying filter modelling. Two major candidates for `time-frequency' (time-varying) spectral characterisation of non-stationary processes are the Wigner-Ville spectrum and Priestley's evolutionary spectrum. Properties, prediction and estimation of the two time-frequency spectra and the relation between them are discussed. The time-frequency spectra of the sound field due to a moving source are predicted and these spectra are used as the basis for estimation of the acoustic directionality pattern of the source. As to the time-varying filter modelling of such non-stationary processes, a technique called the `covariance-equivalent' method is discussed. The covariance-equivalent technique is used to model the sound field due to a moving source emitting a random signal in single-path/single-sensor cases. The covariance-equivalent method, which has only been applicable to single-component processes, is extended to include the sound field in multi-path/multi-sensor cases by using the concept of the complex envelope (complex process). Finally estimation problems of practical importance, including that of (i) the source acoustic directionality pattern and (ii) time-varying delay estimation problems, are formulated and solved in terms of the covariance-equivalent models, and simulation studies are also performed. The simulation results justify that the covariance-equivalent method is an effective characterisation of such non-stationary processes.

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Lee, Jong-Sik (1989) Time-varying filter modelling and time-frequency characterisation of non-stationary sound fields due to a moving source University of Southampton, Institute of Sound and Vibration Research, Doctoral Thesis , 206pp.

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Published date: April 1989
Organisations: University of Southampton


Local EPrints ID: 52248
PURE UUID: 77a6b154-6989-476f-b584-2a2161e9ac68

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Date deposited: 26 Aug 2008
Last modified: 17 Jul 2017 14:43

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Author: Jong-Sik Lee
Thesis advisor: Joseph Hammond

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