Don Pardo (February 22 1918- August 18, 2014) was an American radio and television 'announcer', best known for his work for NBC since the early 1950s. In 1975, by the time of his announcing for "Saturday Night Live", Don was a "trash-culture icon" - his name a 'household word' if you will - for his years with a few wildly popular game shows.
When Frank appeared as guest-host & musical guest on Saturday Night Live in 1976, he had I'm The Slime in the set-list - a song that calls for an 'announcer type' voice. Frank expanded the part to include the 3rd verse that preceded the "Don't touch that dial!" line. Zappa must have been pleased with the result, as he had Don reprise that role for the NYC Palladium run later that month. Don Pardo provided vocal announcements for the albums Zappa In New York and Läther, most memorably during Punky's Whips, I'm The Slime and Legend Of The Illinois Enema Bandit.