Conversation so far:
How did they go about getting the voices of the chipmunks?
The Chipmunks' voices were recorded at half the normal tape speed.
Did they use different people for each of the chipmunks?
Ross Bagdasarian Sr.'s own voice.
How did he come up with the idea?
The technique was by no means new to the Chipmunks.

Question: Did he do this technique with any other characters he came up with?
Self-contained rewrite: Did Ross Bagdasarian Sr. use his own voice with any other characters aside from Alvin and the Chipmunks?