format
Format pitch data as .pitchPP text: one time<TAB>pitchHz line per frame, in chronological order.
Unvoiced frames (pitch <= 0) are written as 0.0 — the convention SonixParser.parsePitchString reads back as unvoiced. The output round-trips through that parser (voiced times/pitches preserved).
Return
.pitchPP file content (trailing newline per line).
Parameters
data
Pitch data (parallel times + pitchesHz).