Postprocessing in Epoch Detection

[Nicole M]

Hi,

why is postprocessing necessary in epoch detection? There are these 2 things that I don’t understand:

1) I thought the main goal of epoch detection is to find a consistent point within each pitch period. Why is it then relevant that this point is on the largest peak?

2) After counting the zero-crossings in the derivative of the waveform: why are the zero-crossings not on the largest peaks/ why do we need to shift our marks? I thought we remove everything besides F0, so each maximum in the waveform (i.e. largest peaks) will correspond to a zero-crossing in the derivative. How can it be that a zero-crossing does not correspond to the largest peak in the waveform?

[Korin Richmond]

> 1) I thought the main goal of epoch detection is to find a consistent point within each pitch period. Why is it then relevant that this point is on the largest peak?

I can think of two reasons: i) notionally, we are seeking to find the very instant of glottal closure (GCI), which is the point of maximum excitation; ii) we would typically want to centre any window (e.g. Hamming or Hann window, when doing PSOLA or other pitch-synchronous processing) at the GCI because maximum energy is there (and also the closed phase just following it).

> 2) After counting the zero-crossings in the derivative of the waveform: why are the zero-crossings not on the largest peaks/ why do we need to shift our marks? I thought we remove everything besides F0, so each maximum in the waveform (i.e. largest peaks) will correspond to a zero-crossing in the derivative. How can it be that a zero-crossing does not correspond to the largest peak in the waveform?

Because signals can be “messy” and the algorithm imperfect 🙂

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