A four-track recorder is a recording tool primarily used to record music. A "track" is a separate channel on a piece of recording media that would typically only contain the sound from one instrument in a musical recording. Therefore, a musician might set up one track with guitar and another track with drums, and so on, allowing all the instruments to be mixed separately and recorded at different times. When it comes to multi-track recording technology, four tracks is generally considered the lowest number of truly useful tracks for most musicians. These recorders were once a mainstay of unsigned music acts, and a standard tool for so-called "garage" musicians, but they have since become less common, partly due to the way digital technology has increased the affordability of more robust options.
When using the four-track recorder, the musician or a group of musicians will record separate instruments on different tracks. One classic technique is something called bouncing tracks, where the audio from two, or sometimes three, tracks is combined together onto one track, leaving the other two tracks open for the addition of more instruments. For most music, having access to only four tracks can make recording difficult, so the use of track bouncing is often required for more complex creations.
There was a time when the four-track recorder was a truly-cutting edge device. Famous popular music groups, like the Rolling Stones or the Beatles, actually used them to record albums. During those days, the idea of multi-track recording was a big deal all by itself since most groups were accustomed to recording without the convenience of splitting tracks up.
The early four-track recorders were based around reel-to-reel tape technology, and they were too expensive for consumers to own. During the 1970s, lower end reel-to-reel devices were released that were inexpensive enough for use in home music studios. In the 1980s, cassette-based four-track recorders became popular, and these were often extremely affordable. It was during the period from about mid 1976 through most of the 1980s when the four-track was a very common device in lower-end home studios. Higher-end studios would have an eight-track recorder or sometimes even a 16-track.
Just like other recording devices, the four-recorder eventually became a digital device with hard-disk-based recording. These work in a similar way to the classic devices, although they have added benefits that aren’t available without the presence of digital technology. The availability of digital hard-drive space has generally led to an overall decline in the popularity of the four-track because more powerful options, like eight-, 16-, and 24-track devices, are much more reasonably-priced than they once were, and the use of computers as recording stations can sometimes allow for many more tracks than any of these.