Recording with magnetism
Before magnetic recording, sound was captured by cutting grooves into wax cylinders or discs. Magnetic recording took a different route: a recording head turns an electrical signal into a varying magnetic field, which magnetizes a moving strip of material. A playback head reads the pattern back and converts it to a signal again. Because the magnetic pattern can be erased and recorded over, the same material can be used many times, and it can also be edited by cutting and joining.
This article traces the medium, magnetic tape, through its main formats. The early wire machines and the German tape machines get a brief outline here, since two companion articles cover them in more detail.
From wire to tape
In 1888 the American engineer Oberlin Smith published a theoretical proposal for magnetic recording, and in the late 1890s the Danish engineer Valdemar Poulsen built the telegraphone, which recorded sound on steel wire and was shown at the Paris exhibition of 1900. Wire recorders found limited use for years, but quality was poor and the signal was weak without electronic amplification. Wire machines became more popular in the 1940s, when they were used by the military and sold as dictation machines and home recorders. Early wire recorders typically used thin stainless steel wire.
The step to tape came in Germany. Fritz Pfleumer patented a paper tape coated with metal powder in 1928, and the electrical company AEG built a machine called the Magnetophon, first shown publicly in 1935, with the chemical company BASF producing the tape on a plastic base. A rediscovery of high-frequency bias, which makes recorded sound much cleaner, improved the quality markedly around 1940. By the end of the Second World War, German radio had machines with sound quality that surprised the Allied engineers who found them.
The postwar spread
Machines and tape brought back by American servicemen, notably Jack Mullin, led to the commercial development of recorders in the United States. The entertainer Bing Crosby, who wanted to pre-record his radio shows rather than perform them live, supported the manufacturer Ampex, which produced professional recorders from 1948. The ability to edit radio programs and music with scissors and splicing tape changed the work of radio broadcasting and recording studios. Tape was cheap, could be reused and offered high quality.
The 3M company in the U.S. supplied tape, and the plastic base moved from acetate to more durable polyester, which resisted stretching and breaking better. The magnetic coating shifted to iron oxide and later to other formulations that increased the signal and reduced noise.
Multitrack and music
Once heads could be stacked, a tape could hold several tracks side by side. Musicians and engineers realized they could record parts separately and combine them later. The guitarist Les Paul was among the best-known experimenters in the 1940s and 1950s, building layered recordings, and the practice grew into the multitrack studio methods that shaped popular music sound for the rest of the century. Studios eventually used machines with 8, 16, 24 or more tracks. The idea of treating a recording as something to be built rather than simply captured came largely from tape.
Reels, cartridges and cassettes
Open-reel tape was the standard for professionals and serious home users from the 1950s. For convenience, manufacturers developed enclosed formats. An eight-track cartridge became popular in cars in the late 1960s and 1970s. The format that lasted longest was the Compact Cassette, introduced by Philips in 1963. Its quality was originally modest, aimed at dictation, but improvements to tape and the Dolby B noise reduction system, introduced in the late 1960s, brought it into the music market. The Sony Walkman, launched in 1979, made the cassette a personal, portable format.
Beyond sound
The same magnetic principle spread to other fields. Computers of the 1950s used magnetic tape for storage, and some of the first computers read programs and data from it. Videotape, first used for broadcasting in the mid-1950s, applied the technique to pictures. Magnetic tape also stored telephone messages in telephone answering machines, which are covered elsewhere.
Decline and legacy
Compact discs, introduced in the early 1980s, offered clean, durable sound, and digital audio files later removed the need for a physical medium. Analog tape recorders declined in everyday use, though some musicians and engineers still prefer tape for its sound, and tape continues to be used for archival data storage in some institutions. Tape has its own preservation problems, since older tapes can shed their coating or become brittle, and recordings may need careful transfer.
Cautions about dates
Several details are disputed or vary by source: who exactly first proposed magnetic recording, the exact dates of early prototypes, and the roles of individual engineers in the German development. The broad sequence of wire, then German tape, then postwar adoption and later cassettes is well established.