Vox Daily has an article discussing film sound design pioneer Ben Burtt on how he developed the vocal effects for Disney/Pixar’s Wall*E:
Ben Burtt related that the most difficult assignment he has ever received as a sound designer was to design voices for characters. His primary challenge was to maintain the soul of a human being while creating a believable, synthesized sound that appropriately matched the characters’ robotic form and features.
A good example of creating a voice for a non-human character is evident in Disney’s film, “Dumbo” (1941), wherein producers used a Sonavox (an artificial larynx) to make a train “speak” with human-like qualities to achieve a desired result. Today, the Vocoder, a digital tool, is used to create a similar yet more sophisticated effect to alter the voice, even modulate pitch.
The Vocoder was used in Wall-E to change the vocal qualities of voice actress Elissa Knight, who performed the voice of Wall-E’s love interest, Eve.
The voice of Wall-E was first performed by Ben Burtt and then manipulated with a digital pen that acted like a joystick, modulating the sound even further.
Continue reading: Ben Burtt and Sound Design for Wall-E [Vox Daily].