In audio, a mix-minus is a particular setup of a mixing console

Mixing console

In professional audio, a mixing console, or audio mixer, also called a sound board, mixing desk, or mixer is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...

, such that the output

Output

Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...

 to a certain device

Information appliance

In general terms, an information appliance or information device is any machine or device that is usable for the purposes of computing, telecommunicating, reproducing, and presenting encoded information in myriad forms and applications....

 contains everything except the input from that device. This prevents echoes

Echo (phenomenon)

In audio signal processing and acoustics, an echo is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single...

 or feedback from reverberating or howling and squealing through the broadcast

Broadcasting

Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...

 or sound reinforcement system.

A mix-minus signal is sometimes also known as a 'clean feed' or a 'Select Audio Return' (SAR). It's worth noting that some broadcast mixing desks, notably those designed in house by the BBC

BBC

The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

 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

Telephone hybrid

Telephone hybrids are an essential functional component of the Public Switched Telephone Network . The term also describes the piece of equipment used in broadcast facilities to enable the airing of telephone callers....

 to a console, at a radio station

Radio station

Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...

. The person on the telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 hears everything playing, including the DJ, except that the caller does not hear his own voice. Mix-minus is also often used together with interruptible feedback

Interruptible feedback

IFB or Interrupted Feedback systems are used in filmmaking and video production for television crew communication, audio monitoring and cueing...

 systems in electronic news gathering

Electronic news gathering

ENG is a broadcasting industry acronym which stands for electronic news gathering. It can mean anything from a lone broadcast journalist reporter taking a single professional video camera out to shoot a story, to an entire television crew taking a production truck or satellite truck on location...

 (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

Digital

A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 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.

Another common example is in the field of sound reinforcement. Consider a room with sound stations for multiple users, each station containing a microphone and a loudspeaker. Such a room might be used in a government house of parliament. The microphone in station #1 would feed the loudspeakers in every other station except station #1. In other words, station #1 receives a mix of all microphones minus the station #1 microphone. This enables all participants to hear each other clearly but minimizes problems with acoustic 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...

.

Mix minus is also used with VOIP calls such as Skype when recording for podcasts, the mix minus removes the caller's voice from the VOIP call, but allows them to hear all other channels available at the mixing desk (mixer).