For the most part, each Muppet is performed and voiced by one person. But there are times when a character might be performed and voiced by separate people. Many characters created by Jim Henson's Creature Shop are voiced and performed by separate people. On Sesame Street a number of Muppet characters have been voiced by non-performers, including various human cast members (like Matt Robinson as Roosevelt Franklin) and songwriters (like Christopher Cerf). For the most part vocals for music numbers are always recorded before taping/filming begins. However, in these cases characters are often still performed by their usual performers to pre-recorded tracks.
Sometimes, there are instances where performers can only voice their regular characters. This includes times when two or more characters from the same performer have dialogue in the same take of the same scene (such as when Big Bird and Oscar the Grouch, both performed by Caroll Spinney, are interacting), as well as times when a performer may be unavailable to be on set but is available to perform the voice at a separate time (such as Frank Oz in Muppet Treasure Island and Muppets from Space).
A number of different methods are used when performers only perform the voices. In the early days, Jim Henson would pre-record the voices and the performers would perform to the pre-recorded tracks. Other times, a performer would perform somebody else's character live as a scene is being shot, while the voice would later be dubbed by the usual performer. Sometimes, the usual performer would record the lines live on the set while another puppeteer would perform the puppetry. These days, this is especially the case with Jerry Nelson and his characters.
- ↑ http://www.toughpigs.com/a-chat-with-jerry-nelson-part-1/ Tough Pigs interview with Jerry Nelson