Beats

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.

Arising from simple interference, the applications of beats are extremely far ranging. 源于简单的干涉，驻波的应用范围极为广泛。 当两个频率不同的声波接近你的耳朵时，交替的 constructive 和 destructive 干涉会导致声音时强时弱——这是一种称为 "拍" 或产生拍的现象。拍频等于两个波频率差的绝对值。 Show 显示

Applications of Beats

Subjective tones 主观音调 Missing fundamental effect 缺失的基本效应 Police RADAR 警察雷达 Doppler pulse detection 多普勒脉冲检测 Radio applications 无线电应用 Mulitphonics 多音

Origin of beats 拍现象的起源 Two tone generators 双音发生器

Envelope of Beat Production

Beats are caused by the interference of two waves at the same point in space. This plot of the variation of resultant amplitude with time shows the periodic increase and decrease for two sine waves.

The image below is the beat pattern produced by a London police whistle, which uses two short pipes to produce a unique and piercing three-note sound.