Here's how it works:
* Pitch Shifting: The voice actor, Richard Steven Horvitz, speaks normally, but the recording is then electronically pitched up. This makes the voice sound much higher and thinner, creating the characteristic "Chipmunk" effect.
* Creative Direction: The creators of Invader Zim chose to give Dim this unique voice to highlight his small size, lack of intelligence, and generally goofy persona. It adds to his comedic character and helps him stand out.
It's important to note that this voice is not a result of a traditional synthesizer, which would create more artificial and distorted sounds. It's simply a clever use of audio manipulation to create a distinctive and memorable character.