The concept of audio mix-minus is to provide remote contributors with a return feed containing the full mix of the program audio except for this remote contributor’s audio – in order to avoid audio loopbacks. If mix-minus is not configured, the job will be done by the built-in echo cancellation algorithm, which doesn't always work perfectly.
Following is an example of a mix-minus setup for 4 remote contributors based on the audio routing features in vMix.
First, you need to enable 4 additional audio mix-buses A, B, C and D in the "Audio Outputs" tab of the vMix "Settings" window.
Then, enable all 4 NDI outputs at the "Outputs / NDI / SRT" tab of vMix "Settings" window.
In the "Output Settings" window, for each NDI output, set "Audio Channels" to BusA, BusB, BusC and BusD respectfully. This will enable audio output of specified audio buses to NDI outputs.
We have configured:
Bus A is the mix-minus for the 1st remote contributor.
Bus B is the mix-minus for the 2nd remote contributor.
Bus C is the mix-minus for the 3rd remote contributor.
Bus D is the mix-minus for the 4th remote contributor.
As shown on the screenshot above:
Guest 1 audio is enabled to all busses except BusA.
Guest 2 audio is enabled to all busses except BusB.
Guest 3 audio is enabled to all busses except BusC.
Guest 4 audio is enabled to all busses except BusD.
All other audio feeds are enabled for all audio busses (Master, BusA, BusB, BusC, BusD).
vMix NDI outputs 1-4 are feeded back via Video Transport to guests 1-4 respectfully.