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SAP2011 uses two contour-derived features: continuity over time, and continuity over frequency. Frequency contours can be detected by the zero crossings of the spectral derivatives. In order to reject artifact, we require that the contours pass a certain contrast threshold. We use a dynamic threshold T calculated for each time window ti and frequency fi as:
Continuity Over Time: For each time window ti we detect all the contours and measure the duration of each contour. The mean duration across the contours is the continuity over time.
Continuity Over Frequency: For each time window ti we detect all the contours and measure the frequency range of each contour. The mean frequency range across the contours is the continuity over frequency.