What Is A Mix Minus?
Mix Minus is a term for a particular audio routing scheme used to provide a mix of everything minus a specific input; mix-minuses are typically used in intercoms systems & talent IFB monitoring for broadcast television & live streams, as well as niche live sound reinforcement applications, where the primary purpose is to eliminate potential echo (caused by round trip latency) or feedback.
Cleanfeed is a term referring to an assignable mix-minus bus often seen on mixing consoles designed for broadcast applications. Though effectively the same thing can be accomplished through groups, aux buses, or matrix outputs.
Why is it important?
Latency & Feedback are two big problems that make communication more difficult if not impossible. It can be quite jarring to hear yourself echoing back to you with a delay. Mix-Minuses are the solution to latency when someone needs to monitor the mix but hearing a delayed version of themselves would be distracting.
A mix-minus is just as it sounds, the audio mix minus a specific corresponding to the input to where that mix is being sent for monitoring. If for example have 3 people that all need to hear one another but not themselves, each would receive a mix minus corresponding to their input being the minus. In the chart, mix 1 would contain inputs 2 & 3, mix 2 would contain inputs 1 & 3, and mix 3 would contain inputs 1 & 2. Each mix might additionally have things like music & effects to aid in cuing, but the overarching concept is the aforementioned routing scheme which can be scaled to much higher channel counts.
Often Mix-minus systems for communication are also combined with automixing technology to provide cleaner audio from each of the open mics.
Example Use Cases
In broadcast television (especially TV News) its common to have remote correspondents in the field talking back and forth with the show host in the TV studio. In scenarios like this a mix minus is used to feed the correspondent a mix of everything going on air except that correspondent to prevent the inherent latency from echoing back in their IFB feed.
Radio Guest Lines
Many radio shows allow callers to dial in on guest phone lines to talk on air with the radio show host. Much like in broadcast television there is a need to keep the caller’s audio from feeding back into the phone line so the caller and hosts can effectively communicate. Without a mix minus you’d have feedback & excessive echo of the callers own voice.
Crew Communication & Intercoms
In production often various crew members need to communicate back and forth. There are plenty of options for purpose built systems from the likes of Clearcom, Studio Technologies, Eartek, Data Video, and more. To allow clear easy communication, everyone needs to be able to hear everyone else in their comm group minus themselves.
In niche live sound reinforcement applications such as court rooms & other government proceedings, there is the need for a large number of people to hear one another while also having minimized risk for feedback. In this context, each position would have a speaker fed a mix of everyone minus their corresponding mic. This allows everyone to hear one another clearly while simultaneously minimizing risk of feedback.