Overdubbing (the process of making an overdub, or overdubs) is a technique used by recording studios to add a supplementary recorded sound to a previously recorded performance.
Tracking (or "laying the basic tracks") of the rhythm section (usually including drums) to a song, then following with overdubs (solo instruments, such as keyboards or guitar, then finally vocals), has been the standard technique for recording popular music since the early 1960s.
Overdubs can be made for a variety of reasons. One of the most obvious is for convenience; for example, if a bass guitarist is temporarily unavailable, the recording can be made and the bass track added later. Similarly, if only one or two guitarists are available, but a song calls for multiple guitar parts, a guitarist can play both lead and rhythm guitar (such as in Cream's "Sunshine of Your Love", when it would have been physically impossible for Eric Clapton to solo and play rhythm guitar simultaneously). Singers who also play an instrument find overdubbing a convenience, since it allows them to focus on one role at a time.
Many vocalists use overdubbing to effectively sing harmony with themselves, as did Patti Page, Harry Nilsson, Laura Nyro, The Carpenters, and George Harrison (who credited himself as the "George O'Hara-Smith Singers"). The members of Queen overdubbed their voices numerous times, to create the chorus effect for "Bohemian Rhapsody". Singers in particular have also used the practice to perfect a recorded performance over several takes. Singer Dusty Springfield is widely reported to have painstakingly assembled individual phrases over time in order to record the ultimate performance. Overdubbing is also used, although less often today, to solidify a weak singer. Multiple unison tracks allow a singer with weak intonation to sound more in tune. The opposite of this is often used with sampled instruments; detuning the sample, however so slightly makes the sound more lifelike.
Numerous recording artists have made albums with only (or mostly) themselves performing, using overdubs to serve as their own 'one-man band'. Such artists include Paul McCartney (McCartney, McCartney II, and 2005's Chaos and Creation in the Backyard), Mike Oldfield (Tubular Bells), Todd Rundgren (Something/Anything?), Emitt Rhodes (Emitt Rhodes, Mirror, Farewell to Paradise), Stevie Wonder (Innervisions), John Fogerty (Centerfield), Ihsahn (The Adversary (album)), Ian Anderson (Walk Into Light, The Secret Language Of Birds), Bill Evans (Conversations with Myself, Further Conversations with Myself), R. Stevie Moore (Phonography (album)) and Prince on many of his 1980s classics.
Overdubbing has sometimes been viewed negatively, when it is seen as being used to artificially enhance the musical skills of an artist or group, such as with studio-recorded inserts to live recordings, or backing tracks created by session musicians instead of the credited performers. The early records of The Monkees were made by groups of studio musicians pre-recording songs (often in a different studio, and some before the band was even formed), which were later overdubbed with the Monkees' vocals. While the songs became hits, many critics cried foul, and Michael Nesmith in particular disliked having to "duplicate someone else's records" for their television show. No cheating was intended in the practice (with the emphasis on the TV program, and with the four members not an experienced group, it was felt that using studio 'ringers' would be more efficient), and numerous other singers and groups had studio help, but this didn't save the Monkees from critical and public scorn.
