How can I make chipmunk or deeper voice (in a voiceover) in iMovie?

that's one of the built-in audio effects of iMovie, no need for 3rd party apps:

• double-click your audio-track

• click the Audio tab

• click the Audioeffect button

• select effect - 'chipmonk'/'James Earl Jones' comes in diff. grades/amounts,

Open> GarageBand> Voice (create+save as+itunes)> Right side, voice= Mouse, Deeper Vocals, etc.> (have Monitor set to ON.)> Record (bottom of screen)> Share> Send to itunes> AAC Encoder i use, and opt what playlist or wherever you want.> Click Share.

It will/should show up in imovie's itunes list. Drag it into Project.

Hope this helps.

You can in GarageBand, and send it to itunes to use in imovie.