Recognition of vehicles by their sounds

Bright, Keith Oscar (1980) Recognition of vehicles by their sounds. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis discusses the identification of descriptors in the signature of a vehicle's acoustic emission; where the signature is a non-stationary signal in the presence of considerable background noise. The investigation has been mainly by computer, which has analysed a large database consisting of segments of many recordings from different types of vehicle. After a review of the unclassified published work of other researchers, the constituent sources are considered that combine to produce the total vehicle sound. A large number of Marina car and Atlantean Double-Decker bus recordings have been obtained under a wide range of operating conditions and these are used to provide a comparison between several digital analysis and feature extraction techniques. It is shown that the spectrum of a vehicle's exhaust noise is modified by a pulse position modulation of the gas pulses that depends on the shape of the exhaust manifold and the firing order. Harmonic series from both the Fundamental Firing Frequency and the Firing Cycle Frequency are generated, with their relative significance dependent on the segment length of the recording and the engine speed. These characteristics are more clearly illustrated by the Inverse Optimum Comb than by the usual autocorrelation. This technique has been developed from the Optimum Comb that is used in speech analysis. Another approach to the selection of descriptors is to examine Homomorphed Spectra for invariant resonances.

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