Mix-minus

Relative to audio engineering, a mix-minus is a particular setup of a mixing console or matrix mixer, such that the output to a certain device contains everything except the input from that device. Mix-minus, which is technically accomplished via a wiring and patching configuration, prevents echoes or feedback from reverberating or howling and squealing through the broadcast or sound reinforcement system.

A mix-minus signal is sometimes also known as a 'clean feed' or a 'Select Audio Return' (SAR), it can be written as N-1. Some broadcast mixing desks, notably those designed in house by the BBC, maintain a separate mix bus for 'clean feeds'. This is technically different, and arguably superior to most implementations of mix-minus, but the end result is the same.

The most common example of mix-minus is when hooking up a telephone hybrid to a console, at a radio station. The person on the telephone hears everything playing, including the DJ, except that the caller does not hear his own voice.

Mix-minus is also often used together with IFB systems in electronic news gathering (ENG) for television news reporters and interview subjects speaking to a host from a remote outside broadcast (OB) location. Because of the delay that is introduced in most means of transmission (including satellite feeds and digital fiber optic connections), the remote subject's voice has to be removed from his earpiece. Otherwise, the subject would hear himself with a slight (but very distracting) delay.

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