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.
To enable automated mix-minus for Web Guests you have to pick one source in the Publisher application that you are going to send as the return feed to guests, right-click at this studio feed, open the Settings window and set “Web Guest Mix-Minus enabled” to “true”, restart the feed and you are ready to go. All the guests connected to Web Guest URL will have their own personal mix-minus and will hear everyone else connected to the same Guest URL.
All mix-minus creation is handled inside Publisher application automatically for up to 8 guests.
The studio feed should contain only audio originated from the studio, you have to exclude all the guests from that mix. Video Transport application will add all necessary guests automatically while creating personal mix for each guest.
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.