Sound & Pitch: To PointProcess (cc)

A command to create a PointProcess from the selected Sound and Pitch objects.

Purpose

to interpret an acoustic periodicity contour as the frequency of an underlying point process (such as the sequence of glottal closures in vocal-fold vibration).

Algorithm

The voiced intervals are determined on the basis of the voiced/unvoiced decisions in the Pitch object. For every voiced interval, a number of points (or glottal pulses) is found as follows:

1. The first point t1 is the absolute extremum of the amplitude of the Sound, between tmidT0 / 2 and tmid + T0 / 2, where tmid is the midpoint of the interval, and T0 is the period at tmid, as can be interpolated from the Pitch contour.
2. From this point, we recursively search for points ti to the left until we reach the left edge of the interval. These points must be located between ti–1 – 1.2 T0(ti–1) and ti–1 – 0.8 T0(ti–1), and the cross-correlation of the amplitude in its environment [tiT0(ti) / 2; ti + T0(ti) / 2] with the amplitude of the environment of the existing point ti–1 must be maximal (we use parabolic interpolation between samples of the correlation function).
3. The same is done to the right of t1.
4. Though the voiced/unvoiced decision is initially taken by the Pitch contour, points are removed if their correlation value is less than 0.3; furthermore, one extra point may be added at the edge of the voiced interval if its correlation value is greater than 0.7.

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© ppgb, March 22, 1998