Comb Filtering When two or more identical audio streams are blended together with a short delay between them, comb filtering occurs. Because frequencies in phase add together, while frequencies out of phase cancel, the resulting frequency response graph resembles a comb. Phase Interference Understanding the principles of phase interference helps understand why comb filtering occurs.  Constructive Interference Take a glance at the sound waves below. The frequencies of the waves are identical. They're also in phase, which means the waves rise and fall in unison. They add together and generate a sound wave that is double the original size since they are in phase and have the same amplitude. It's like adding 2 numbers. This phenomenon is known as constructive phase interference. Destructive Interference The sound waves in this image are completely out of phase. This means that when one w...