Click the Audio Mixer button on the right hand side of the main interface to bring up the Audio Mixer tab as shown below.

Each fader also includes an Audio Level Meter for the Left and Right channels respectively.

Detach Button

The Audio Mixer can be detached from the main vMix window by clicking the Pin button.

To dock the Audio Mixer back again, click the Minimise button of the detached Audio Mixer window.

Outputs

The Master audio mix is displayed here alongside Bus A and B if they have been configured.

Headphones volume can be configured independently by spinning the Headphone volume control knob.

Inputs

Each Input that contains audio will be displayed here.

Audio Settings

Click the cog  button to display the Audio Settings window.

Solo

Click the  Solo button to preview Input audio in the Headphones without affecting the mix.

Solo audio is Post-Effects and Post-Fader and will be audible even if the Input is muted.

Mute

Click the  speaker icon to Mute/Unmute an audio input.

Automatically Mix Audio

Click the  Green and Orange Arrow button to enable/disable automatic mixing of audio.

This option is also known as "Follow" on traditional video switchers.

Audio Buses

vMix allows for up to three independent audio buses to allow for complex audio routing scenarios including mix minus.

M

M is the Master or Default audio mix and is sent to Recording, Streaming and External Output.

A, B

A and B are two additional audio mixes that are sent to the A and B Audio Output devices configured in the Audio Outputs settings window.

Click the M, A or B buttons underneath each input to configure each independent each mix. By default all new inputs will be sent to the Master mix only.

Note: The Speaker/Mute button controls the audio for all audio buses not just the Master or M bus.

Collapsing Mixers

All mixers can be collapsed and restored by right clicking the Title of the mixer.