So what’s the difference between harmonics and formants in singing, and why does it matter?
Harmonics come from the vocal folds. They are considered to be the source of the sound. You change the harmonics present by changing the shape & thickness of the vocal folds, therefore changing the pitch of the sound. Different harmonics have different energy, or intensity.
Easy enough, right?
So formants are where it gets slightly stickier. Formants are created by the shape of the vocal tract, and they act as a filter for the pitch.
What does that mean? It means that all the work you are doing in your voice lessons to adjust your articulators — i.e. your lips, jaw, tongue, and soft palate, is work to adjust the resonance frequencies of the formants. You’re literally changing the dimensions of the resonance cavities in the vocal tract in order to add depth to, or filter, the pitch created by the harmonics.
Check out this article from Auditory Neuroscience to see spectrograms of different words and see harmonics and formants in action!