Summing a signal with its delayed copy creates perceived pitch.

Evidence

An example of pitch generated by coloured noise is repetition pitch. In repetition pitch, a broadband signal such as noise or a rapid transient is delayed and summed to the non-delayed signal. The perceived pitch corresponds to the frequency that is the reciprocal of the delay. In signal processing this is known as the comb-filter effect, where the spectrum of the signal has evenly spaced peaks and valleys. The frequency of the first peak in the comb-filter spectrum corresponds to the repetition pitch (Bilsen and Ritsma, 1969). — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1111

Categorization

• DEFINE: Defines repetition pitch and connects it to the comb-filter effect — a clear conceptual framework.
• XREF: Connects to audio engineering knowledge of comb filtering and flanger/phaser effects, and to echo perception.
• SHARE: Worth sending to someone into audio DSP or acoustics — the concrete reciprocal-of-delay relationship is the neat nugget.