Just spitting trough my backup harddisk and found some software. Amadeus II, Felt Tip Sound Studio 2.0 and Cubase VST 5 (the last one only runs on classic, the other two even on 10.6.8 ).
oooohhh an a lot of games...
/Edit: just played whit those 2. Sound Studio 2 is a very simplified software, olny cost 49,99 and the new version only 29,99. Amadeus is a little older, has noise filters, but hard to handle, not at that easy. And the results are not what i had in mind, but that could be cause the handling. Did not played whit Cubase yet.
But i also found a demo version of Soundsoap 2. Will give it also a try.
.Edit2: just googled Cubase 5 an found out it is from 2009, but mine is much older and only runs on Classic, so it must be Cubase VST 5.