A mix-minus is a term that is often used in a podcast or live video production. It refers to a specifically mixed audio signal that is sent back to a remote guest or caller on the podcast or live stream. The mix-minus allows them to listen to any other hosts or guests, without hearing themselves as a delayed echo.
While the audio mix for the show must contain all the audio tracks from all hosts and remote guests, the mix-minus that gets sent back to the remote guest does not contain their own incoming audio signal. It is essentially the main mix, minus their own incoming audio signal.
Due to latency in internet audio, if the remote guest’s audio track was not removed from the return signal being sent back to them, they would hear themselves in their own ears a fraction of a second after they spoke. This latency-induced echo makes it nearly impossible to concentrate and speak in a regular way and can cause feedback.
Bob and Joe have a podcast. They record the podcast from a studio, sitting next to each other. They each have their own microphones which are sent into a mixer on input 1 and input 2. These are mixed into the main track.
The podcast always has a guest that calls in using Skype. The Skype call is picked up by a computer, and the audio output of the computer is sent out to the mixer on input 3 and mixed into the main track. At this point, the main track is a mix of input 1, input 2 and input 3. This mix is what is recorded for the podcast.
But we are missing one vital part. The guest cannot currently hear the two hosts so we need to create a second mix that is sent back to the computer to use as Skype’s audio input. This is where we create a mix-minus. Using your mixer, you create a second mix that only contains Bob and Joe’s mic inputs 1 and 2. This mix is sent back to the computer so that the guest can hear Bob and Joe, but they cannot hear themselves. Voila! A mix-minus. A mix of the hosts, minus the mix of the guest.
Of course in order to do this, you do need to have a mixer that is capable of creating both a primary mix, and a secondary mix for the mix-minus. Make sure you consult the manufacturers mixer specifications to see if this is an option on any mixer you are likely to purchase.