Time-frequency distribution of evoked otoacoustic emissions

Otoacoustic emissions (OAE) are non-stationary signals that vary in time depending on the characteristics of the stimulus. Traditional spectral analysis using Fourier methods ignores the effects of time and can miss important temporal information. Therefore, a better form of spectral analysis requires the use of time-frequency distribution methods. Traditionally, short time Fourier transforms (STFT), commonly known as spectrograms, are used to provide such time-frequency representations. STFT however, suffer from poor resolution and do not provide enough detail about the characteristics of the emissions. In this study, recently developed time-frequency distributions, the Wigner Distribution (WD) and the Choi-Williams Distribution (CWD) are investigated to provide high resolution representations of transient evoked OAEs. Although WD has excellent properties for time-frequency analysis, it suffers from cross-term artefacts generated when multiple sinusoids are present. CWD provides a solution to this problem at the expense of poor time and frequency support. In this study, we use both distributions to estimate the cross-products and provide a relatively artefact-free time-frequency distribution of OAEs. This method is applied to both click and tone burst evoked OAE and shows a more detailed time-frequency representation with as many crests and valleys as different latencies.