Realistic periodic sound sources generate many harmonics, not single frequencies.

Evidence

We have so far focused on sinusoidal driving of a system—that is, just one frequency present in the drive. Such sinusoidal driving can be arranged electronically, but reeds, lips, vocal folds, fipples, bows, and the like are not sinusoidal, even though they may be periodic. Anything that abruptly but periodically opens and shuts, or sticks and slips, cannot be described by a single smooth sinusoid. Such drives supply many harmonics to the system simultaneously. Almost all realistic periodic drives generate many harmonic partials of a fundamental drive frequency. — Eric J. Heller, Why You Hear What You Hear- An…, 1745

Categorization

• DEFINE: Defines sinusoidal vs. periodic drives and why real instruments generate harmonics, not single pure tones.
• XREF: connects to: The source excites all harmonics even when a resonator only supports odd ones. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1255