The period of summed sinusoids equals the lowest common period

Evidence

In the case shown, the smaller fork is vibrating faster than the larger fork by a factor of 3/2. Notice that the period of the sum of the two sinusoids, cos(2π · 200t) + cos(2π · 300t), is double that of cos(2π · 200t)—that is, 0.01 second. This fact will play a large role later, when we consider the perception of pitch. — Eric J. Heller, Why You Hear What You Hear- An…, 306

Categorization

• QUESTION: Why does the perception of pitch track the period of the sum — a key mechanism worth chasing for the ‘why we hear what we hear’ question.