@Stef, could you please attach a fileout with the fixed method? I think that it is just one method change, so I can put that in the inbox and make sure it gets included in trunk.
There are actually three methods, one for MixedSound, one for RepeatingSound and one for SequentialSound. You may want to recategorize them.
I also attached a modification for AbstractSound>>#loudness which uses the amplitude envelope when it is present. I do not remember why I did this, but I'm confident that works :) But please do not take my code for granted and review it.
Stef