Hopefully this will get you started. there is a plugin that is usually by default enabled called Audio Capture. You can use it to add an audio capture component to your player, and then you will get access to the microphone.
For this example I have turned the activation to auto, and set it to only send the audio to the bus (otherwise I can hear myself through the computer speakers as well).
There is an event that the component gets called On Audio Envelope value that triggers any time the mic changes, note that my guess is this will have a similar overhead to using on tick, as it will most likely be constantly changing. I’ve attached an example gif of the shown print screen changing the red value of my print node.
Edit: You might consider digging through this other forum thread for potentially more information and insight: [How to use new Audio Capture Component (4.19) to drive game parameters? - Audio - Unreal Engine Forums][1]
