A Pitch object represents periodicity candidates as a function of time.
[ref: Praat help, https://www.fon.hum.uva.nl/praat/manual/Pitch.html]
p$xmin ... start time (seconds)
p$xmax ... end time (seconds)
p$nx ... number of frames
p$dx ... time step = frame duration (seconds)
p$x1 ... time associated with the first frame (seconds)
p$t ... vector of time instances associated with all frames
p$ceiling ... a frequency above which a candidate is considered voiceless (Hz)
p$maxnCandidates ... maximum number of candidates in frame
p$frame[[1]] to p$frame[[p$nx]] ... frames
p$frame[[1]]$intensity ... intensity of the frame
p$frame[[1]]$nCandidates ... actual number of candidates in this frame
p$frame[[1]]$frequency ... vector of candidates' frequency (in Hz)
(for a voiced candidate), or 0 (for an unvoiced candidate)
p$frame[[1]]$strength ... vector of degrees of periodicity of candidates (between 0 and 1)