In music, modulation is most commonly the act or process of changing from one key to another. This may or may not be accompanied by a change in key signature. Modulations articulate or create the structure or form of many pieces, as well as add interest.
A recurring gag within the Muppets' musical performances is a character announcing a modulation just before it occurs by shouting "modulate!" This tells the other characters (or, in some cases, the audience) that it's time for a quick key change.
According to biographer Brian Jay Jones, while Jim Henson could not read sheet music and often joked that he could barely sing, his passion more than made up for his lack of technique. During music rehearsals on The Muppet Show, Henson would sing with gusto gleefully announcing a key change by calling out "modulate!"—a habit that Henson carried over into many of his characters, and a quirk that amused Frank Oz so much that he incorporated it into the performances of many of his characters too.
- When singing "Cottleston Pie" in episode 107 of The Muppet Show, Rowlf explains to the audience "now this is where the song changes key, what we call modulation" before he changes to G-sharp minor. Rowlf does the same when performing the song on Ol' Brown Ears is Back saying "now this is where the song does what you call modulate."
- Rowlf shouts "up a key!" to inform the chorus to modulate during the performance of "(Hey Won't You Play) Another Somebody Done Somebody Wrong Song" in episode 112 of The Muppet Show.
- Fozzie tells Rowlf to modulate when the two are playing "English Country Garden" in episode 218 of The Muppet Show.
- Marvin Suggs shouts at the Muppaphone to modulate before their final (completed) chorus of "Witch Doctor" in episode 304 of The Muppet Show. Since each Muppaphone member is individually tuned to one note, the aggrived aggregation accomplishes this by switching positions.
- Fozzie tells the Muppets to modulate during the "Brotherhood of Man" musical number in I Love Liberty.
- Kermit and Robin announce their modulation during the opening theme for the Muppet Babies "Yes, I Can" videos.
- As the dogs' weeping escalates while singing "Man's Best Friend" in The Muppet Show episode 404, Rowlf shouts "modulate!" and the howling intensifies. Similarly, when he performed the song again on Ol' Brown Ears is Back (as "Old Dog Trey"), he shouts "modulate!" as the music shifts from solo piano to a full instrumental complement.
- Gonzo tells Rizzo to modulate when the two are singing "It's the Most Wonderful Time of the Year" on A Green and Red Christmas. Gonzo also tells the Muppets (Kermit, Fozzie, Miss Piggy, Rizzo and Pepe) to modulate during their performance of the song during 2009's "Christmas in Rockefeller Center."
- During Hiram and Burt's ode to dirt in a 2010 episode of Sesame Street, their song starts a modulation; Oscar moans, "Not a key change!"
- Bert calls for a modulation during "Telephone Talk" in the Sesame Street Live show, Big Bird's Sunny Day Camp Out.
- Ernie calls for modulation during his and Bert's nighttime rendition of "What's the name of that song?"
- In "Good Things Come to Those Who Wait," Cookie Monster remarks "Key change!" when a modulation occurs.