I looked at Gater a bit more. You are right, things are strange. Applying the effect creates a new wav file. My original seems to have been overwritten with the first apply.

Any further changes seem to use the new file from the last apply, so things get very wierd. I need to do more testing to better understand how this works.

Best to make and use copies of files before doing this. At least Ctrl+z (undo) works.

Create a single note 4 bars long. Do some testing by increments and note the results of changing the number at the bottom. Try volume and filter. As far as I can tell, each number corresponds to a different sound characteristic. Watch the wave form change after each change (on the object after applying). The wave forms seem to correspond to the wave that is shown in the image with the corresponding colour.

Also, I noted a bug in MMM2015 Premium. I recorded a single midi note, compiled it, trimmed it using T, and deleted the part at the right. Then I applied a Gater effect, Undo, opened Gater, selected a random effect, and pressing on Test sometimes does nothing except that I noticed that the scissors at the top of the screen toggled off and on.