Alvin and the Chipmunks, originally David Seville and the Chipmunks or simply The Chipmunks, is an American animated music group created by Ross Bagdasarian Sr. for a novelty record in 1958. The group consists of three singing animated anthropomorphic chipmunks: Alvin, the mischievous troublemaker, who quickly became the star of the group; Simon, the tall, bespectacled intellectual; and Theodore, the chubby, impressionable one. The trio is managed by their human adoptive father, David (Dave) Seville. In reality, "David Seville" was Bagdasarian's stage name, and the Chipmunks themselves are named after the executives of their original record label.
The Chipmunks' voices were recorded at half the normal tape speed onto audiotape by voice talent (on the 60's records, generally Ross Bagdasarian Sr.'s own voice overdubbed three times, on the post-80's records, studio singers) talking or singing at half the normal speaking rate. When the tape was played back at normal speed, they would sound a full octave higher in pitch, at normal tempo. The technique was by no means new to the Chipmunks. For example, the high and low pitched characters in The Wizard of Oz were achieved by speeding up and slowing down vocal recordings. Also, Mel Blanc's voice characterization for Daffy Duck was sped up to some extent. Now, the same effect is created digitally and in real time with a pitch shift. However, the extensive use of this technique with the Chipmunks, coupled with their popularity, linked this technique to them. The term "chipmunk-voiced" has entered the American vernacular to describe any artificially high-pitched voice. A similar effect could be obtained in playback by merely taking an LP recorded at 33 1/3 RPM and playing it back at 45 or 78 RPM, a trick sometimes tried out by ordinary record listeners. The instrumental portions of the song are sped up as well, however, making it obvious that the music is being played at the wrong speed. Bagdasarian recorded vocals and music at different speeds to combine properly on his recording. Guitarist Les Paul said he visited Bagdasarian's studio in 1958 and helped with the recording. The technique was used extensively in the British puppet show Pinky and Perky, which pre-dated the Chipmunks. The sound was frequently imitated in comedy records, notably "Transistor Radio" by Benny Hill, "Bridget the Midget" by Ray Stevens, "The Laughing Gnome" by David Bowie, and on several tracks on Joe Meek and the Blue Men's album I Hear a New World. The technique also appears in the "Yeah! You!" line of The Coasters' "Charlie Brown". Prince used the technique on several of his songs, as well as Frank Zappa on We're Only In It For The Money and on the instrumental album Hot Rats, among others. The early production style of hip-hop artist Kanye West involved sped-up, high-pitch vocal samples from classic soul records incorporated with his own (additional) instrumentation. Due in part to the acclaim of his debut album The College Dropout, such sampling techniques subsequently became much copied by a myriad of other hip-hop producers. In the early '90s rave scene, many breakbeat hardcore productions would utilize the same studio tricks, often taking a cappella from house records and speeding them up to fit the faster tempo. Vocals in songs that used this method would typically be referred to as "chipmunk vocals".

Q: How did they go about getting the voices of the chipmunks?
A: The Chipmunks' voices were recorded at half the normal tape speed onto audiotape by voice talent
Did they use different people for each of the chipmunks?
on the 60's records, generally Ross Bagdasarian Sr.'s own voice overdubbed three times, on the post-80's records, studio singers on the 60's records, generally Ross Bagdasarian Sr.'s own voice overdubbed three times, on the post-80's records, studio singers generally Ross Bagdasarian Sr.'s own voice overdubbed three times, Ross Bagdasarian Sr.'s own voice
Ross Bagdasarian Sr.'s own voice