The simple answer is that the mic input is probably being fed out to a speaker output which in turn is being picked up by the mic again, causing a feedback loop.

Quick fix - turn the speaker volume down or, better still, use headphones.

More complicated fix. In the Settings, in the Audio Outputs section, make sure the Master Output is not fed to your Speakers.
You can have the Headphones mix fed to the Speakers, but, if so, go to the settings for the Mic input (in the Mixer section, via the Gear wheel for that input) and turn the Headphones volume right down for input with the Yeti mic. That way, you can listen to other audio via the Headphone mix (eg. From playback of video files) but not get the mic signal sent back out. You will still have to watch the playback level if using speakers rather than headphones for monitoring, or else that Headphone output mix will be picked up by the mic input (unless you fade the mic volume when playing other audio).

What vMix is doing is emulating aspects of how a hardware audio mixer might work, so some knowledge of audio engineering in general is useful when using the audio side of vMix.

@ zenvideo & stamperplus

Also note that the latest release (vMix 20.0.0.30), clicking on the now green headphone icon in the Audio Mixer Settings of an Input is a way to "quick mute" the Input's audio to your PC Speaker/headphone Output (but maintain Output to Master for Streaming/Recording).


Ice