Ringing out is a process in audio engineering

Audio engineering

An audio engineer, also called audio technician, audio technologist or sound technician, is a specialist in a skilled trade that deals with the use of machinery and equipment for the recording, mixing and reproduction of sounds. The field draws on many artistic and vocational areas, including...

 used to prevent audio feedback

Audio feedback

Audio feedback is a special kind of positive feedback which occurs when a sound loop exists between an audio input and an audio output...

 and maximize volume. It involves a sound technician raising the slider controls on a mixing desk to cause an audio system to feedback. Once feedback occurs, the technician uses the graphic equalizer to pull back the appropriate band (or frequency) a few dB (decibels). This is repeated until the technician is happy with the sound of the room, roughly three times.