There was a discussion a while ago regarding changing pitch/Amplitude of all the files along with other things in one go. Well here is one tool that claims it can do it. I have not used it though but appears to be a good tool
Batch processing supports up to 32000 files allowing you to apply effects and/or convert your files as a single function.
http://www.apple.com/downloads/macosx/audi...itorformac.html
WavePad Audio Editor for Mac 3.14