Form is only as render-intensive as you make it, there are
tons of ways to make it render in near realtime if you limit
the numbers of particles or threads and are creative with the
effect.�
Not only that, but any effect in AE can be made
sound-reactive.
1. import audio, select audio track
2. Animation -> keyframe assistant -> convert audio
to keyframes
3. You now have an hour-long track of keyframes, take any
effect, enable expressions, and pickwhip the effect parameters
to the audio keyframe track
4. One place to start would be fractal noise parameters to
animate, or size / position keyframes on shape layers, or
shape layer repeater effects
5. look up the linear(x, x, x, x) expression - this will
conform, say -360 to 360 degree rotational values into a 1-100
number scale that the audio keyframes work with
