When two sound waves of different frequency approach your ear, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud - a phenomenon which is called "beating" or producing beats. The beat frequency is equal to the absolute value of the difference in frequency of the two waves. If you listen real hard, beneath the roar of rampant advertisement and consumerism you'll hear the sound of disenchantment. You'll hear the voices, all out of tune. You'll hear...the beat frequency.