How do you add effects to your voice?
Have a go with 'Audacity'...
It's a full feature sound recording app., and unlike Windows 'sound recorder', it runs indefinitely.
It takes a bit of gettin' use to, but once you do, you'll luv it.
Record (with headset/mic) your voice in Audacity, then play around with the tempo, speed, etc. (in 'Effects' I think) to get it like you want.
Don't forget to save the file as well as the recording itself, so you can have the exact same settings so your next recording is identical to the first.
Freeware.
http://audacity.sourceforge.net/
And this plug-in will extend the range of Audacity to work with Mp3 files:
http://downloads.sourceforge.net/lame/la…
90 additional 'Effects' plug-in's are here:
http://audacity.sourceforge.net/beta/lad…
(These are the PC sites; Mac (compatible) may not be on same pages, but sourceforge has it.)