Objectives
The term fundamental frequency appears in many voice science papers. It is defined as the lowest frequency of a periodic waveform. The objective is to show the confusions that can exist when there is no clear periodicity or a single harmonic series.

Methods
The approach is conceptual and computational. Nonperiodic signals that contain subharmonics, missing harmonics, modulations, and bifurcations are examined.

Results
Energy-dominance in low-frequency components, individually and in clusters, is likely to be a factor in extending fundamental frequency beyond a single harmonic series.

Conclusions
There are no firm conclusions at this point. Some consensus is needed by scientists and practitioners to reach some agreement for vocalizations not characterized by single harmonic series.