Check low pitch against harmonics even when two trackers agree

Two pitch trackers can both report half the perceptually dominant frequency during irregular or alternating glottal pulses. For a proposed sustained register drop, inspect the waveform's periodicity and odd versus even harmonic power around the candidate frequency and its octave-up alternative. Classify weakly voiced spans as unresolved instead of forcing a low-pitch or false-alarm verdict. This distinguishes tracker behavior from stronger acoustic evidence but still cannot certify perceived pitch or naturalness; phone-band listening or a validated assessor remains necessary.

Applies when: screening reference-conditioned speech for brief deep-register events in narrowband output. Keywords: TTS pitch tracker octave halving period doubling harmonics autocorrelation narrowband voice