The first record to feature multitracking was released by Capitol Records in 1947. On it, the legendary guitarist Les Paul was heard playing eight different guitar parts; a feat he achieved by recording one part to a wax disk, then recording another disk while playing along with the first. This process continued until the final recording featured all eight guitar parts. This was revolutionary, if a little time-consuming and impractical, and Paul began working on modifying an Ampex tape recorder by adding additional playback and recording heads. This was, in effect, the first multitracker. This lead to the commercial release of Ampex's "Sel-Sync" (Selective Synchronous Recording) recorder in 1955.
These early magnetic tape machines were two and three track models and the popular music artists of the day were quick to embrace the new technology. By the early 1960s, leading recording groups of the era such as The Beatles and The Beach Boys continued to push the boundaries of what these machines could accomplish, and by the mid-60s were using 4-track machines linked together to offer even more tracks to record with.
As the decade continued, 8-track machines gained in popularity, and by 1968 Ampex introduced their new 16-track recorder to the world, offering musicians even more multitracking options. The age of analog tape recording would hold sway over the recording industry until the 1990s when the digital recording age ushered in computer recording software that allowed for almost unlimited overdubbing.
In rhythm-based pop music, the multi-tracking process starts with the drums and bass tracks. Each drum usually is assigned to its own track so that the engineer can have total control of how the drum set will sound and how it will be placed, or "panned" in the stereo field. The bass guitar will also have its own track, and assuming that the playing is in synch and the song's arrangement is a good one, these rhythm tracks will form the solid rock upon which the rest of the song can be built. From there, different instruments like guitars, keyboards and extra percussion can be added one by one.
If it's an acoustic-based recording without drums, the rhythm track will often be a metronome, or "click" track. This too, will be recorded, so that musicians can play along with it and ensure that the song will have an even tempo. This track will then be discarded at mixdown. The lead and harmony vocals are often the last parts to be added, but a temporary rough or "guide" vocal is often assigned to a track so that musicians adding tracks can better follow the flow of the song as they add their parts.
After the parts have all been recorded, the song is ready to be mixed. This is where all of the separate musical parts are mixed together to create a cohesive-sounding two-track stereo mix. Because each of the recorded parts reside on their own track, they can each be separately manipulated during mixing by means of equalization (EQ) and the use of effects like reverb, delay and compression, in order to have them blend together in a smooth and musical way.
Multitracking affords a recording engineer total control over every facet of a recording. Each track that is recorded has its volume level, tone and placement in the stereo image easily controlled by a fader, knob or the click of a mouse. Even if recordings are made with a band playing live in the studio, each part is still assigned to its own track, and any inadequacy in the sound can be corrected by making changes to that particular track without affecting any of the others. Multitracking is particularly beneficial to solo artists who happen to be multi-instrumentalists, in that they are able to function as a one-man-band, constructing complex pieces of music one track at a time.
Though analog tape is sometimes still used for multitracking, the convenience and cost-effectiveness of computer recording has made it a niche product. Tape machines are expensive and notoriously demanding to maintain, which makes them impractical for widespread use. Many analog die-hards insist that vintage tape equipment delivers a warmer and more pleasing sound than digital recordings, but the digital realm offers more flexibility and editing options. Recording software allows for endless overdubbing without the need for bulky tape recorders and large mixing consoles, allowing musicians to work on multitracked creations for very little financial investment.
Having an almost unlimited number of tracks can be a blessing and a curse. While it is certainly convenient to be able to record dozens of takes, keep them all, and wait until mixdown to decide which parts to use, having this comfort zone can sometimes be at the expense of creative decision-making. Having to sift through endless takes when mixing, in order to pick and choose tracks to edit together perfect performances, is also very time consuming, and there are those who would argue that the time might be better spent working harder on the song's arrangement before tracking. There is certainly something to be said for having a musical vision and committing to it from the start. When George Martin and The Beatles were recording their classic songs on 4-track machines in the 60s, they had no such flexibility in this regard. Unlike digital recording, where you can keep all recorded tracks, the restrictions of tape meant that to free up tracks for vocals, they'd have to bounce instrumental tracks together to create a mix of the instruments (a sub-mix), knowing that once it was committed to tape, it couldn't be changed, since the originally recorded instrumental tracks would have to be erased to allow for the recording of the vocals. You'd be hard-pressed to find anyone who'd argue that Strawberry Fields Forever would have sounded better if the Beatles would have had more options at mixdown!