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Either for diagnostics purposes or NVH improvement efforts in vehicle development, it will be necessary to have both timing and spectral contents information from measured sound or vibration data. It will become especially important when the sound or vibration is induced from the impact mechanism in automotive engines, such as valve train, piston, or fuel injector etc. In this study, we will review several approaches of time-frequency representation, like Wavelet Transform, Wigner-Ville Distribution and Short-Time Fourier Transform, with their properties in view of application to practical development engineering. These techniques have been applied to practical development examples in order to identify the characteristics of the impact-induced sound and vibration [1, 9]. From the valve train noise study, it was possible to separate valve seating noise at the time of valve closing, and valve opening noise during valve opening period.