Microphone input volume to axis value translation

Hello everyone,

I want to make a voice chat program which features, amongst other things, mouths in the shape of simple circles, squares or triangles. I want these objects to scale up and down with the volume of the sound input. I looked into the reference for this, and all I found was AudioListener.GetOutputData and GetSpectrumData. The reference is terrible on these two, though, and I can't figure out how to translate the volume of whatever's being said to a simple Axis that'd control the mouth scaling. does anyone have any idea how to do this? Just a general idea would be nice to have.

Thanks in advance!