In music, tape loops are loops of magnetic tape used to create repetitive, rhythmic musical patterns or dense layers of sound when played on a tape recorder. Originating in the 1940s with the work of Pierre Schaeffer, they were used among contemporary composers of 1950s and 1960s, such as Éliane Radigue, Steve Reich, Terry Riley, and Karlheinz Stockhausen, who used them to create phase patterns, rhythms, textures, and timbres. Popular music authors of 1960s and 1970s, particularly in psychedelic, progressive and ambient genres, used tape loops to accompany their music with innovative sound effects. In the 1980s, analog audio and tape loops with it gave way to digital audio and application of computers to generate and process sound.
In a tape loop, a section of magnetic tape is cut and spliced end-to-end, creating a circle or loop which can be played continuously, usually on a reel-to-reel tape recorder, making the sound repeat endlessly.
Simultaneous playing of tape loops to create patterns and rhythms was developed and initially used by musique concrète and tape music composers, and was most extensively utilized by Steve Reich for his "phasing" pieces such as "Come Out" (1966) and "It's Gonna Rain" (1965), and by Karlheinz Stockhausen in Gesang der Jünglinge (1955–56) and Kontakte (1958–60). Stockhausen also used the technique for live performance in Solo (1965–66).
If, instead of simply playing back a recorded loop, something is done to progressively alter the recorded material between cycles, such as re-recording the sound before it passes the playback head or adding new material to the loop, then a process of change will occur in the content, quality and complexity of the material.
On a standard reel-to-reel tape recorder, one loop can be no more than few seconds long. Some composers were satisfied with this approach, but there were other methods to allow for longer loops. For example, placing two reel-to-reel machines side by side with the tape path running from the one to the other. By using this method, some composers could create very long loops which allowed for sounds of greater duration. When recording his landmark 1978 ambient album Music for Airports, Brian Eno reported that for a particular song, "One of the tape loops was seventy-nine feet long and the other eighty-three feet". The longest tape loop ever created was made by Barry Anderson for performances of Stockhausen's Solo.
By accelerating the speed of a loop to a sufficient degree (e.g., 1,280 times faster), a sequence of events originally perceived as a rhythm becomes heard as a pitch, and variation of the rhythm in the original succession of events produces different timbres in the accelerated sound. The maximum available acceleration of most three-speed tape recorders is four times.
In the late 1940s, Pierre Schaeffer used special phonograph discs with a sillon fermé (closed groove) to repeat segments of sounds in his musique concrète studio in Paris. When magnetic tape technology became available, he replaced this technique with tape loops, where such segments could either be simply repeated, or could undergo electronic transformation during repetition.
In 1955, Éliane Radigue, an apprentice of Pierre Schaeffer at Studio d'Essai, learned to cut, splice and edit tape using his techniques. However, in the late 60s she became more interested in tape feedback. She composed several pieces (Jouet Electronique , Elemental I , Stress-Osaka , Usral , Ohmnht  Vice Versa, etc ) by processing the feedback between two tape recorders and a microphone.
Halim El-Dabh, who experimented with tape music from the early 1940s to the 1950s, also utilized tape loops. Beginning in the late 1950s, the BBC Radiophonic Workshop began using tape loops to add special effects to some BBC programming. Several different configurations of tape loops were employed in the early years of the WDR Studio in Cologne. One such arrangement was used to build up multilayered textures by sequentially recording sounds with the erase head disconnected or with a customised arrangement of the heads. Gottfried Michael Koenig applied this method in 1954, in his Klangfiguren I.
In Canada, Hugh Le Caine produced "a particularly clear and memorable example of musique concrète" in 1955 titled Dripsody. It was built from the sound of a single drop of water, using a variable-speed tape recorder, tape loops, and just 25 splices. At this same time in Cologne, Karlheinz Stockhausen produced a more ambitious work, Gesang der Jünglinge (1955–56), which made extensive use of tape loops, particularly for its stratified impulse groups and choral swarms.
Minimalist composer Terry Riley began employing tape loops at the end of the 1950s. Using simple Wollensak tape recorders, he recorded piano music, speech and other sound samples, which he would reproduce on speakers surrounding the audience along with live performance, creating "orchestral textures", as Edward Strickland puts it. With assistance of Richard Maxfield and Ramon Sender, Riley combined tape loops with echoplex devices, producing an "acid trip" piece Mescalin Mix (1961), made from sound samples from his earlier works. Later, he experimented with combining different tapes together, producing pieces such as Music for the Gift (1963) and culminating in his use of a tape delay/feedback system employing two tape recorders (collectively described by Riley as the "time lag accumulator") in live solo performances.
The use of tape loops in popular music dates back to Jamaican dub music in the 1960s. Dub producer King Tubby used tape loops in his productions, while improvising with homemade delay units. Another dub producer, Sylvan Morris, developed a slapback echo effect by using both mechanical and handmade tape loops. These techniques were later adopted by hip hop musicians in the 1970s.
Steve Reich also used tape loops to compose, using a technique which he called "phasing". He would put two tape loops together at slightly different speeds, so they would start playing simultaneously and then drift apart. Pieces created by this method are It's Gonna Rain (1965) and Come Out (1966). In Violin Phase (1967) he combined the tape loop with an instrumental score. Later on, Gavin Bryars explored a similar concept in composition 1, 2, 1-2-3-4 (1971), played by a small ensemble in which every musician independently tried to reproduce tape recording.
In the 1960s and 1970s, use of tape loops made a breakthrough in popular music. As they progressed towards their "psychedelic" phase, the Beatles increasingly experimented with new technology and tape recorders, a process which culminated with Revolver (1966) and its last track "Tomorrow Never Knows", based on five tape loops running simultaneously. "Revolution 9" (1968) was an even more experimental venture, consisting almost entirely of tape loops fading in and out.
Introduction of new technologies, such as analog music sequencers and synthesizers in the 1970s, followed by digital sequencers in 1977, marked an end of the tape loop era in the music industry. With the advent of MIDI in 1983, computers and digital devices took over the production of sound effects from analog devices. Tape loop compositions have seen only sporadic revivals since, such as William Basinski's The Disintegration Loops series (2002–2003), evidencing the slow death of his tapes originally recorded in the 1980s.