Compact audio cassette
From Freepedia
The compact audio cassette medium for audio storage was introduced by Philips in 1963 under the name Compact Cassette. Although there were other magnetic tape cartridge systems at the time, the Compact Cassette became dominant as a result of Philips' decision (in the face of pressure from Sony) to license the format free of charge. It went on to become a popular (and re-recordable) alternative to the vinyl record deck during the 1970s. During the 1980s, its popularity grew further as a result of the Sony Walkman.
Although its use in the West has declined as a result of more advanced technologies, it remains widespread, and is still the dominant medium for listening to music in many third world countries.
In essence, the audio cassette is simply a cassette-based (and smaller) version of the older reel-to-reel tape format. It consists of two miniature reels, between which an oxide-coated plastic tape, or magnetic tape, is passed and wound. These reels (along with some other mechanical parts) are held inside a protective plastic shell.
Four single audio tracks are available on the tape. These are paired up to produce two stereophonic tracks – one played when the cassette is inserted with its 'A' side facing up, and the other when it is turned over (with the 'B' side up), thus mimicking gramophone records.
The mass production of compact audio cassettes began in 1965 in Hanover, Germany, as did commercial sales of prerecorded music cassettes, known as musicassettes or MC for short. However, as the system was initially designed for dictation and study use, the audio quality of many early systems was poor. Early models also had a reputation for chewing the tape. Despite this, they also found favour in dictation machines and portable tape recorders. As time went on, various improvements (in particular, the introduction of Dolby noise reduction) resulted in the format being taken more seriously for musical use.
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Features of the cassette
The cassette was a great step forward in convenience from reel-to-reel audio tape recording, though because of the limitations of the cassette's size and speed, it initially 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. This permitted monaural cassette players to play stereo recordings "summed" as mono tracks and permitted stereo players to play mono recordings through both speakers. The tape is 1/8 inch (3.175 mm) wide, with each stereo track being 1/32 inch (0.79 mm) wide and moves at 17/8 inches per second (47.625 mm/s). For comparison, the typical open reel format was ¼ inch (6.35 mm) wide, each stereo track being 1/16 inch (1.5875 mm) wide, and running at either 3¾ or 7½ inches per second (95.25 or 190.5 mm/s). Some machines were able to use 17/8 inches per second (47.625 mm/s) but the quality was poor.
Cassette types
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 approach that of vinyl records. Cobalt doped ferrite was introduced by TDK and proved very successful. Sony tried a dual layer tape with both ferrite and chrome dioxide. Finally pure metal particles as opposed to oxide formulations were used. These each had different bias and equalization requirements requiring specialized settings. Ferrite tapes use 120 μS equalization (known as Type 1), while chrome and cobalt doped tape types require 70 μS equalization (Type 2). In practice the cassette shell was modified with indents to automatically select the proper bias and equalization on compatible cassette decks.
Noise reduction and fidelity
A variety of noise reduction schemes are used to increase fidelity, Dolby B being almost universal for both prerecorded tapes and home recording. Later enhancements included Dolby C noise reduction, Dolby HX-Pro headroom extension, automatic bias setting and automatic head azimuth adjustment. By the late 1980s, thanks to such improvements in the electronics, the tape material and manufacturing techniques, as well as dramatic improvements to the precision of the cassette shell, tape heads and transport mechanics, sound fidelity on equipment from the top manufacturers far surpassed the levels originally expected of the medium. On suitable audio equipment, cassettes could produce a very pleasant listening experience. The best home decks could achieve 20-20kHz frequency response with wow and flutter below 0.05%, and 70dB of signal-to-noise ratio; far better than records and approaching that of CD.
Playback length
Tape length is usually measured in minutes total playing time, and the most popular varieties are C46 (23 minutes per side), C60 (30 minutes per side), C90, and C120 (usually thinner tape, more likely to be destroyed in use). Some vendors are more generous than others, providing 132 meters or 135 meters rather than 129 meters of tape 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. Other lengths are (or were) also available from some vendors, including C15 (useful for saving data from early home computers), C50, C70, C74, C80, C100 and C110. Except for C74 and C100, such non-standard lengths have always been hard to find, and tend to be more expensive than the more popular lengths. Home taping enthusiasts may have found them useful for fitting an album neatly on one or both sides of a tape. For instance, the initial maximum playback time of compact discs was 74 minutes, explaining the relative popularity of C74 cassettes. See also audio tape length and thickness.
Write-protection
All cassettes include a mechanism to prevent re-recording and accidental erasure of important program material. Each side of the cassette has a plastic tab on the top that may be broken off, leaving a small indentation in the shell. This indentation allows the entry of a sensing lever which prevents the operation of the recording function when the cassette is inserted into a cassette deck. If the cassette is held with one of the labels facing the user and the tape opening at the bottom, the write-protect tab for the corresponding side is at the top-left.
If later required, a piece of adhesive tape can be placed over the indention to record over the "protected" material, or (on some decks), the lever can be manually depressed to record on a protected tape. Extra care is required when doing this with high bias tape cassettes; the additional indents (adjacent to the write-protect tabs) used to differentiate them from normal bias cassettes should not be inadvertantly covered up. One manufacturer, Bib even made small plastic inserts to fit into the record tab indent, and a special tool for removing them.
Applications
Audio
The compact cassette was originally intended for use in dictation machines. In this capacity, some later-model casette-based dictation machines could also run the tape at half speed (15/16 IPS) as playback quality was not critical. The Compact Cassette soon became a popular medium for distributing prerecorded music—initially through Philips's record company, PolyGram. Starting in 1979, Sony's Walkman helped the format become widely used and popular. In 2005, one finds cassettes used for a variety of purposes such as journalism, oral history, meeting and interview transcripts and so on, however, they are starting to give way to compact disc and more "compact" storage media. In many countries with restrictive political systems, cassettes serve as a cheap and easily concealed means for dissidents to distribute banned political speeches to large numbers of people thus circumventing government censorship. In immigrant communities, cassettes carried by travelers have served as an important means to transmit news, messages and culture between separated family members and communities.
Home studio
In the 1980s, Tascam introduced the Portastudio line of four and eight-track cassette recorders for home studio use, allowing amateur musicians (and some professionals) to overdub themselves easily. To increase audio quality in these recorders, the tape speed is doubled in comparison to the standard; additionally, dbx noise reduction provides compression which yields increased dynamic range. Multi-track cassette recorders with built-in mixer and signal routing features provide a wide range of features and benefits from easy-to-use beginner units up to professional level recording systems.
Home dubbing
Most cassettes were sold blank and used for recording (dubbing) 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 1979 Sony brought out the Walkman, a small portable cassette player which greatly increased the popularity of listening to music on the go. Cassettes were also a boon to people wishing to make bootlegs (unauthorized concert recordings) for sale or trade, a practice tacitly or overtly encouraged by many bands with a more counterculture bent such as the Grateful Dead.
Various legal cases arose surrounding the dubbing of cassettes. In the UK, in the case of CBS Songs vs Amstrad (1988), the House of Lords found in favour of Amstrad that producing equipment that facilitated the dubbing of cassettes, in this case a twin cassette deck that allowed one cassette to be copied directly onto another, did not constitute the infringement of copyright.
Data recording
Many early home computers of the 1970s and early 1980s, notably the TRS-80, Commodore PET, VIC-20, Commodore 64, TI-99/4a, ZX Spectrum, Amstrad CPC, Coleco Adam, Apple, and BBC Micro, could use cassettes as a cheap alternative to floppy disks as a storage medium for programs and data. The typical encoding method was simple FSK which resulted typical data rates 500 to 2000 bit/s, although some games used special faster loading routines, up to around 4000 bit/s. A rate of 2000 bit/s equates to a capacity of around 660 kilobytes per side of a 90 minute tape.
The usage of both audio channels, better modulation techniques like QPSK or those used in modern modems, combined with the greater bandwidth and Signal to noise ratio of cassette tapes compared to a PSTN telephone line could have been used for achieving much greater capacities and speeds (several kBytes/s for data rate, and several MBytes on each cassette), but such a solution wasn't adopted since it would require much more expensive decoding/encoding circuitry on the computers or on dedicated "datacorders", apart from good quality tapes and recorders with constant performance.
Cassette equipment
Cassettes can be played on a wide variety of different types of device. Early recorders tended to be small battery-powered portable devices, in keeping with the intention of the medium for dictation, reportage and similar low-level recording duties, but by the mid 1970s, the cassette deck became a commonplace component of home high fidelity systems, largely superseding the reel-to-reel recorder for home use. Another key element of the cassette's success was its use in in-car entertainment systems, where the small size of the tape was significantly more convenient than the competing 8-track cartridge system. Cassette players in cars and for home use were often integrated with a radio receiver, and the term "casseiver" was occasionally used for combination units for home use. In-car cassette players were the first to adopt the idea of automatic reversal ("auto-reverse") of the tape at each end, allowing a cassette to be played endlessly without manual intervention. Home cassette decks soon followed this practice as well.
Successors to the cassette
Technical development of the cassette effectively ceased when digital recordable media such as DAT and MiniDisc were introduced in 1992. Philips introduced the Digital Compact Cassette — a DAT-like tape in the same form factor as the compact audio cassette — but this attempt failed in the market. Since the rise of cheap CD-R discs, the phenomenon of "home taping" has effectively switched to compact disc. The microcassette has in many cases supplanted the full-sized audio cassette in situations where voice-level fidelity is all that is required, such as in dictation machines and answering machines. Even these, in turn, are starting to give way to digital recorders of various descriptions. However, there are also some mp3 players shaped as audio cassettes available, which can actually be used as if it is a normal cassette in any audio cassette player.
Compact disc sales overtook cassette tape sales in 1993.
Present and future of the compact cassette
Despite the wide availability of higher-fidelity media, audio cassettes are still being produced and marketed in many countries and are still popular in some applications such as car audio and other difficult environments, because they tend to be more rugged and more resistant to dust, heat and shocks than most digital media (especially CDs) and their lower fidelity is not a very serious drawback inside the typically noisy interior of most automobiles. CD players as of late have had "shock proof" technology which stores an amount of information in a memory buffer in case of a skip. Storing some portion of the audio in a memory buffer allows the player to recover more easily from shocks.
Cassettes (often in the form of microcassettes) are also used in business and educational settings as adjuncts or substitutes for note-taking. While digital voice recorders are becoming available, tape recorders tend to be universally cheaper and of sufficient quality to do the job.
Also, cassettes and related equipment are still popular in many parts of the world, where digital audio technology has not yet caught on.
Cassettes and related equipment will probably be manufactured until 2010 or 2015, after which the fate of the audio cassette will likely be similar to that of vinyl records or rather, of the common photographic film (limited, niche market production). As of 2005 it is common for otherwise-complete audio systems to be sold with only a single cassette tape deck instead of two, with playback-only decks, or even with no cassette deck at all. Many cars are now being equipped with CD rather than cassette as standard, and many new cars come with integrated entertainment units with no space to add or even connect external cassette players, with little complaint from auto users.
Cassette in other languages
In French and in Catalan the word "cassette" is abbreviated as "K7" (ka-sept); the "K7" shorthand also works in Portuguese: cá-sete. In Spanish it is known by the letters KCT (pronounced "ka-cé-te").
See also
- Cassette culture
- Cassette single ('cassingle')
- Digital cassettes
- Elcaset
- Electronic journalism
- List of audio formats
- Microcassette
- Mix tape
- PXL-2000 - A toy camcorder that used compact audio cassette to store video.
External links
- An interesting look at the cassette vs the iPod
- Images of hundreds of different blank cassette styles
