I'm not sure how it's implemented on the JS side, but I can imagine the CSS getting a lot of updates per second as the voice level changes, constantly interrupt

I'm not sure how it's implemented on the JS side, but I can imagine the CSS getting a lot of updates per second as the voice level changes, constantly interrupting the current animation. Might be worth it to buffer the input until animationEnd() event fires. That might reduce the amount of calculations and redrawing that needs to be done. Or the CSS engine is robust enough to handle continual updates and this won't solve a thing. I'd have to test it.