Cumulative Intensified Wave Effect

[BreakerZero]

Exactly as it sounds. Essentially I am wondering if someone could do something like this but cumulative in its intensity (like start with zero and build to 0.25 in terms of amplitude). And preferably in reverse as well.

 

[BreakerZero]

Should have probably also mentioned this but by cumulative I also mean that the effect seamlessly builds up to full intensity without any interruption whatsoever.