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Compact audio cassette

For the meaning of cassette in genetics, see cassette (genetics).

The compact audio cassette audio storage medium, sometimes known as the musicassette, was introduced by Philips in 1963. It consists of a length of magnetic tape inside a protective plastic shell. 4 tracks are available on the tape, giving 2 stereo tracks - one for playing with the cassette inserted with its 'A' side up, and the other with the 'B' side up, thus mimicking gramophone records. There were other magnetic tape cartridge systems at the time, but the compact cassette succeeded through Philips' backing. The mass production of compact audio cassettes began in 1965 in Hannover, Germany, as did commercial sales of pre-recorded music.

The cassette was a massive step forward in convenience from reel-to-reel recording, though the limitations of the cassette's size and speed compared poorly in quality. Unlike the open reel format, the two stereo tracks lie adjacent to each other rather than a 1/3 and 2/4 arrangement. The tape is 1/8 inch wide (3.175mm), with each stereo track being 1/32 inch wide (0.079375mm) and moves at 17/8 inches per second (47.625 mm/s). For comparison, the typical open reel format was ¼ inch wide (each stereo track being 1/16 inch wide) and running at either 3¾ or 7½ inches per second.

The original magnetic material was based on ferrite (Fe2O3), but then chromium dioxide (CrO2) and more exotic materials were used in order to improve sound quality to try to match those of vinyl records. These had different bias requirements, requiring more complicated equipment.

A variety of noise reduction schemes were used to increase fidelity, Dolby B being almost universal for both prerecorded tapes and home recording. By the late 1980s, sound fidelity on equipment by manufacturers such as Nakamichi and Tandberg far surpassed the levels expected of the medium by early detractors and on suitable audio equipment could challenge the sound quality of the compact disc.

Tape length was usually measured in minutes total playing time, and the most popular varieties were C60 (30 minutes per side), C90, and C120 (usually thinner tape, more likely to be destroyed in use - especially the C120). Some vendors were more generous than others, providing 132 m or 135 m rather than 129 m for a C90 cassette. C180 and even C240 tapes were available at one time, but these were extremely thin and fragile and suffered badly from effects such as print-through which made them unsuitable for general use.

The cassette had originally been intended for use in dictation machines, but quickly became a medium for distributing prerecorded music - particularly through Philips' record company, PolyGram - with an option for home recording use. Cassettes were also used for purposes such as journalism, field history, meeting transcripts and so on. In the 1980s, Tascam introduced the Portastudio, a four-track recorder for home studio use, which increased the audio quality possible on cassette by doubling the tape speed and using DBX noise reduction (which worked by compression to increase the dynamic range).

Most cassettes were sold blank and used for recording the owner's records (as backup or to make compilations), their friends' records or music from the radio. This practice was condemned by the music industry with such slogans as "Home taping is killing music". However, many claimed that the medium was ideal for spreading new music and would increase sales, and strongly defended at least their right to copy their own records onto tape. In the late 1970s, Sony brought out the Walkman, a small portable cassette player, which greatly increased the consumption of music in this manner. Cassettes were also a boon to people wishing to make bootlegs (unauthorised concert recordings) for sale or trade.

Many home computers of the 1980s, notably the TRS-80, Commodore 64, ZX Spectrum, Amstrad CPC and BBC Micro used cassettes as a cheap alternative to floppy disks as a storage medium for programs and data. Data rates were typically 500 to 2000 bps, although some games used special faster loading routines, up to around 4000 bps. A rate of 2000 bps equates to a capacity of around 660 kb per side of a 90 minute tape.

Technical development of the cassette effectively ceased when digital recordable media such as DAT and MiniDisc were introduced. Philips attempted to introduce the Digital Compact Cassette - a DAT-like tape in the same form factor - but it failed in the market. Since the rise of cheap CD-R discs, the phenomenon of "home taping" has effectively switched to compact disc.

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