Did you try keyframing the Mask Shape, that works on my machine, leaving Stroke or Audiowaveform the same size as the Mask Shape enlarges (Audiowaveform: Path – Mask 1, and the same layer selected as the audio layer, display option: Analog Lines, = no real audio waveform bouncing, only a cool stroke)? You could also decrese the stroke/Audiowaveform) as the circle increases, or wiggle it (ooo, I like that, hadn’t done it before), your choice.
To get uniform Mask shape change, double click the mask, and Ctrl + Shift drag a corner (like doing a PhotoShop Transform).
Shift keeps it circular, Ctrl makes it expand from the center.
Audiowaveform: Path – Mask 1 (I’m assuming the Mask is on a Solid Layer, with “none” instead of “Add” for the Mask type, and the same layer selected as the audio layer (don’t tie it to an real audio layer), display option: Analog Lines, = no real audio waveform bouncing, only a cool stroke)?
You might be saying “What’s with this Audiowaveform?”, I dunno, I like it most times better than Stroke, what with the inner and outter color, but then I was always a sucker for Neon Lights.