The 3-to-1 Rule is a rule of thumb for microphone placement. When microphones are placed too close together, unwanted dips and peaks in frequency response occur as a sound source is picked up by more than one mic. This translates to poor sound quality. When placing your mics, the distance between adjacent mics should be approximately three times the distance between the mic and the sound source. For example, if a singer is about one foot away from the mic, the next mic should be placed about three feet away from the first mic. At this distance, the sound that reaches other mics is soft enough to avoid interference.