Because of the phase cancellation effect caused when a sound is mixed with a delayed copy of itself, the resonance or attenuation (strengthening or weakening) of the frequencies caused by that delay is heavily dependent on the delay time. If a sinusoidal component of a sound is delayed by exactly one cycle (i.e., one period, i.e.
When a sound is mixed with a delayed version of itself, each sinusoidal component of the delayed sound has a unique phase offset compared to the original, so each frequency is accentuated or attenuated differently. For example, if a 1000 Hz sinusoid is delayed by 1/1000 of a second (1 millisecond), the original and the delayed version will still be perfectly in phase, so that frequency will be increased in amplitude when the two versions are added together.
This patch demonstrates how to adjust the delay time of a comb filter to make the filter correspond to a desired fundamental pitch.