The "choral effect" occurs when people who stutter speak or sing in unison with others and their stutter is dramatically reduced or even eliminated. By allowing the user to hear their own voice with a pitch shift, a slight time delay or a combination of both, DAF and AAF creates the illusion of another speaker speaking at the same time. Delay is in milliseconds and is software driven. The idea is that almost simultaneous echo engages so-called mirror neurons (brain cells). As a result, it proposes that this innate mimicking ability overrides whatever in the brain that causes stuttering.