The sound hasn’t been edited – the fading in and out is a natural consequence of cascading multiple instances of this algorithm. This can be viewed as the Central Limit Theorem in action. In signal processing terms, this means that cascading a whole bunch of similar filters will result in an impulse response that approximates a Gaussian curve.
A single instance of the plugin as used to generate this effect sounds like this (with wet/dry mix set to 50%):
The plugin by itself can be set up to produce a Gaussian attack and decay, where the sound fades in over a few seconds:
However, cascading several instances produces a more dramatic version of the same effect. To me, it sounds very similar to the sounds obtained by extreme time stretching.
Progress continues on the plugin. It is in the hands of beta testers, and I am resolving the bugs that are coming up. I hope to make an official announcement in the next few days.
EDIT: I just made the first announcement of the new plugin, ValhallaShimmer. Check it out here.