The first commercially available tape recorders were monophonic, that is, they had only one track on which to record sound on magnetic tape. In the late 1940s and early '50s, some progressive musicians began to experiment with "overdubbing." They would play a song on an instrument, record it on tape and then play it back and record it onto a second tape recorder, while at the same time using a microphone to record another part, creating a "one man band."
Magnetic tape has an inherent "hiss" characteristic. With each successive overdub, the hiss became more objectionable. In addition, the first recording lost some quality as it was rerecorded. The process of overdubbing was clumsy and produced a low-fidelity product.
In 1953, noted guitarist Les Paul, who had been using overdubbing, commissioned the Ampex company to build a recorder that could record eight individual tracks. By 1955, Ampex had produced the first commercial multitrack tape recorder. Using a process Ampex called "Sel-Sync" (for Selective Synchronous Recording), the performer could record on one track while listening back to previously recorded tracks, and they would all be synchronized.
By the late 1950s, two-track multitrack tape recorders were commonly being used. However, the two tracks were mixed down to produce mono recordings, as records and radio stations were all mono media. Typically, one of the tracks would be used for recording instruments and the second for vocals, allowing flexibility in balances between the two when mixing.
By 1960, Ampex manufactured a three-track machine incorporating Sel-Sync and using 1/2-inch wide tape (1/4-inch had been the norm). RCA also started making multitrack tape recorders as early as 1957, recording Elvis Presley, and in 1958, Buddy Holly used a three-track machine. As stereo records and stereo FM radio became popular, engineers used two tracks on these machines for a stereo image of the instruments (left and right channels) while using the third track for vocals, which would typically be centered (in both channels) in the mix.
Studios began installing four- and eight-track machines in the early 1960s, and by the end of the decade, Ampex had a 16-track recorder on the market. Rock and pop musicians including The Beatles, Tommy James and the Shondells, Frank Zappa, Genesis, David Bowie, Queen and others were all using multitrack recorders regularly. Recording history was made when Wendy Carlos released her album "Switched-On Bach" in September of 1968, using a Moog synthesizer and an eight-track recorder. Robert Moog wrote in the book that accompanies a CD release of those original works, "Wendy's contribution to this revolution cannot be overstated." In the 1970s, TEAC introduced two four-track recorders that were designed for the home consumer market. Eventually, 24-track machines using two-inch wide tape became the recording studio norm, and techniques were devised to sync two or more of these machines together, yielding track counts of 48 and more.
As computer technology advanced, digital recording, as opposed to analog recording, eliminated the problem of tape hiss. Digital audio tape (DAT), however, is being replaced today with hard-disk recording, and the era of multitrack magnetic recording is coming to an end.