This paper summarizes the main properties of six time-frequency representations, and describes their application to the visualization of typical helicopter rotor noise traces. Time-frequency representations may be a useful tool for the visual analysis of helicopter rotor noise, because they provide Information not available from time- or frequency-domain representations alone, such as the time variations of the spectrum of the signal or its power spectrum, which translate in distinctive patterns on a time-frequency plot. No single representation is best for all cases. The Short-Time Fourier Transform and the spectrogram seem to have the most general usefulness. The Wigner-Ville distribution is useful when the noise events are well separated in time. The Choi-Williams distribution does not offer a significant practical improvement over the Wigner-Ville distribution. The Continuous Wavelet Transform and the scalogram do not appear to offer major advantages over Short-Time Fourier Transform and spectrogram, possibly because the Gaussian mother wavelet used in this study is not specifically tailored for helicopter rotor noise. Time-Frequency Representations require some tuning to achieve the most informative results; the specific parameters depend on the representation. This tuning is typically simple, and is not a major practical obstacle.
Time-frequency visualization of helicopter noise
Zeit-Frequenz-Visualisierung von Hubschrauberlärmemissionen
Journal of the American Helicopter Society ; 46 , 4 ; 262-272
2001
11 Seiten, 14 Bilder, 11 Quellen
Article (Journal)
English
Rotor (Drehflügel) , Geräuschemission , Lärmminderung , Frequenzbereich , Visualisierung , Signalverarbeitung , Leistungsspektrum , Schallenergie , Fourier-Transformation , Spektrogramm , numerische Analysis , numerische Simulation , Rechenmodell , statistische Verteilung , Wavelet-Transformation , Abstimmen (Frequenz)
Time Frequency Visualization of Helicopter Noise
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