Compact audio cassette

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Image:Tdkc60cassette.jpg The compact 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 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.

Contents 1 History 2 Features of the cassette 2.1 Cassette types 2.2 Noise reduction and fidelity 2.3 Playback length 2.4 Write-protection 3 Applications 3.1 Audio 3.2 Home studio 3.3 Home dubbing 3.4 Data recording 4 Cassette equipment 4.1 Maintenance 5 Present and future of the compact cassette 5.1 Successors to the cassette 6 Cassette in other languages 7 See also 8 References 9 External links

History

The compact audio cassette medium for audio storage was introduced by Philips in 1963 under the trademark 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, with cassette sales overtaking those of LPs. (Vinyl overall remained ahead due to greater sales of singles, although cassette singles achieved popularity for a period in the 1990s). Image:CompactCassetteLogo.gif 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.

The mass production of compact audio cassettes began in 1965 in Hanover, Germany, as did commercial sales of prerecorded music cassettes (also known as musicassettes; MC for short). The system had been initially designed for dictation and portable use, thus the audio quality of early recorders was not well suited for music. Some early models also had unreliable mechanical design. In 1971 the introduction of Dolby type B noise reduction and chromium dioxide tape by Henry Kloss resulted in the format being taken seriously for musical use.

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 3.18 mm wide (nominally ¹⁄₈ inch), with each stereo track being 0.79 mm wide (¹⁄₃₂ inch) and moves at 4.76 cm/s (1⁷⁄₈ ips) from left to right. For comparison, the typical open reel format in consumer use was ¼ inch (6.35 mm) wide, each stereo track being ¹⁄₁₆ inch (1.59 mm) wide, and running at either 3¾ or 7½ inches/sec (9.5 or 19 cm/s).

Image:CassetteTypes1.jpg

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. The most common, Ferrite tapes (known as Type I) use 120 µS equalization, while chrome and cobalt-doped tapes (Type II) require 70 µS equalization. Metal Cassettes (Type IV), also use 70 µS equalization, and provide still further improvements in sound quality, as well as improved resistance to wear. The quality is normally reflected in the price; Type I cassettes are generally cheapest, and Type IV usually the most expensive. BASF developed a chrome cassette designed for use with 120 microsecond equalisation but this idea only really caught on for commercial pre-recorded cassettes.

Image:Cassette Write Protect IV.jpg Notches (indents) on top of the cassette shell indicate the type of tape within. Type I cassettes only have write-protect notches, Type II have an additional pair next to the write protection ones, and Type IV (metal) have a third set in the middle of the cassette shell. These allow cassette decks to automatically detect the tape type and select the proper bias and equalization.

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 and Dolby S noise reduction, Dolby HX Pro headroom extension, the dbx and DNR noise reduction systems, automatic bias setting, and on some high-end decks, automatic head azimuth adjustment. Dolby HX Pro, which was developed by Bang & Olufsen, is a system that dynamically alters the bias during recording to yield a substantial improvement in high-frequency response during playback, regardless of the playback system.

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 Hz-20 kHz frequency response with wow and flutter below 0.05%, and 70 dB of signal-to-noise ratio using Dolby C and up to 80 dB of signal-to-noise ratio using Dolby S.

In the 1990's, Dolby S noise reduction was introduced to the compact cassette, derived from Dolby SR, a professional system. Whereas the Dolby B and C Noise Reduction would dynamically adjust the preemphasis to promote a lower noise floor for high frequencies, Dolby S worked across the frequency range. However, licensing restrictions meant that Dolby S was only available on higher end tape decks that included dual motors, triple heads and other refinements. This system, according to a double blind study conducted by Stereo Review, yielded more accurate results than MiniDisc.

Prior to the mid 1980's pre-recorded cassettes were often of abysmal sound quality mainly due to the high speed duplication process used to produce them. However, technologies such as XDR (a quality control system), Dolby B Noise Reduction, Dolby HX pro and chrome dioxide tape meant that pre-recorded cassettes were soon approaching vinyl records in terms of audio quality and outselling LP records in some markets.

Playback length

Image:Cassetteinternals.jpg Tape length is usually measured in minutes total playing time. The most popular varieties are C46 (23 minutes per side) and C60 (30 minutes per side), C90, and C120. The C46 and C60 lengths are typically 15-16 µm thick, but C90s are 10-11 µm and C120s are just 9 µm thick rendering them more susceptible to stretching or breakage. 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 C10 and 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 write protection 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 inadvertently 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 cassette-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' 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 of the earliest microcomputers implemented the Kansas City standard for digital data storage. Later on, most home computers of the late 1970s and early 1980s, such as the

• TRS-80,
• Commodore PET,
• Commodore 64,
• ZX Spectrum,
• Apple,
• BBC Micro, and the
• Amstrad CPC

could use cassettes for program and data storage as a cheaper alternative to floppy disks. Even the first version of the IBM PC (1981) had a cassette port and a command in its ROM BASIC programming language to use it. However, this was seldom used, as even then floppy drives had become commonplace in high-end machines. The typical encoding method was simple FSK which resulted in 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 use of better modulation techniques like QPSK or those used in modern modems, combined with the improved bandwidth and signal to noise ratio of newer cassette tapes allowed much greater capacities and speeds (10–17 kilobytes/s for data rate, and up to 60 MB on each cassette). These were typically used as hard disk backup for PCs in the late 1980s. They also found use during the 1980s in data loggers for scientific and industrial equipment.

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.

Later on Cassette tape adaptors were developed, allowing newer forms of music player to be used with existing cassette-based systems, including those in cars. (See "Successors to the cassette" below).

Companies such as Tandberg, ReVox, Nakamichi, Akai, Aiwa, Technics, Pioneer and Sony made highly advanced cassette decks for high-end audio systems. Some include three-head technology for off-tape monitoring.

Maintenance

Cassette equipment needs regular maintenance, as cassette tape is a magnetic medium which is in physical contact with the tape head and other metallic parts of the recorder/player mechanism. Without such maintenance, the high frequency response of the cassette equipment may suffer.

One problem occurs when iron oxide (or similar) particles from the tape itself become lodged in the read head. As a result, the tape heads will require occasional cleaning to remove such particles. The metal capstan and the rubber pinch roller can become coated with these particles, leading them to pull the tape less precisely over the head; this in turn leads to misalignment of the tape over the head azimuth, producing noticably unclear high tones, just as if the head itself were out of alignment.

In addition, the heads and other metallic components in the tape path (such as spindles and capstans) may become magnetically charged, and require demagnetization. Both Cassette demagnetizers and head-cleaning fluid are available. Isopropyl alcohol is commonly used as a tape head cleaner.

Present and future of the compact cassette

In many western countries, the market for cassettes has declined seriously since its peak in the late 1980s. This has been particularly noticeable with pre-recorded cassettes, whose sales were overtaken by those of CDs during the early 1990s. Since then, the pre-recorded market has undergone further serious decline, with a large proportion of retailers having dropped them altogether.

However, as of early 2006, cassettes are still produced; blank cassettes are sold at most retail stores, and facilities for cassette duplication remain available. Cassette recorders and players are gradually becoming scarcer, but are still widely available.

Despite the wide availability of higher-fidelity media, they also remain popular for specific applications, including:

• Car audio and other difficult environments. Cassettes are typically more rugged and resistant to dust, heat and shocks than most digital media (especially CDs). Their lower fidelity is not considered a serious drawback inside the typically noisy automobile interior. Although the "shock proof" buffering technology in many new CD players allows time to recover from intermittent skips, the cassette remains more resilient in the face of periodic and repeated shocks. However, cassettes generally have poor resistance to the excessive levels of heat encountered in parked cars during the summertime.

• Adjuncts or substitutes for note-taking in business and educational settings. Whilst digital voice recorders are becoming available, compact cassette (or frequently microcassette) recorders tend to be cheaper and of sufficient quality for this purpose.

• Audiobooks, church services, and other spoken word material are still frequently sold on cassette; low fidelity is generally not a drawback for such content. Whilst most publishers also sell CD audiobooks nowadays, most will still offer a cassette version at a lower price.

In other countries, particularly in the third world, cassettes remain the dominant medium for purchasing and listening to music.

However, it is clear that cassettes and related equipment are in serious decline, and are likely to become increasingly marginalised as time goes on. 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 automobile users.

Successors to the cassette

Technical development of the cassette effectively ceased when digital recordable media such as DAT and MiniDisc were introduced in the late 1980s and early 1990s.

In 1992, Philips introduced the Digital Compact Cassette (DCC), a DAT-like tape in the same form factor as the compact audio cassette. It was aimed primarily at the consumer market. Unlike DAT (which had found a niche in professional usage), DCC was not a success, and was discontinued in 1996.

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.

MP3 players shaped as audio cassettes have become available, which can be used in any audio cassette player as if it were a normal cassette. Similarly-shaped audio adapters are also sold, providing an economical and effective way to obtain CD and/or MP3 functionality in vehicles equipped with cassette decks. The MP3 player (or a similar device) has its analog line-out connected to the adapter, which in turn feeds the signal to the head of the cassette deck. Where a cassette deck is not available, an FM modulator (which sends the signal to a car's FM radio) can be used instead.

Cassette in other languages

The word "cassette" is French in origin, so it was acceptable to the Academie Française without calling for them inventing a new word for it, as they have for many devices in the computer industry.

A popular alphanumeric abbreviation comes from the word's pronunciation /ka ˈsɛt/ in French, which is the same as that for K7 in that language. The same holds true for Catalan. And even though the pronunciation is different /ˈka sɛ tɛ/ in Portuguese, the abbreviation K7 works for them as well.

In Spanish it is popularly abbreviated by the letters KCT (pronounced /ka ˈsɛ tɛ/).

See also

Template:Commonscat

• Cassette culture
• Cassette single ('cassingle')
• Digital cassettes
• Elcaset
• Electronic journalism
• List of audio formats
• Microcassette
• Minicassette
• Mix tape
• PXL-2000 - A toy camcorder that used compact audio cassette to store video.

References

• Robert Angus. "History of Magnetic Recording", Audio (August/September, 1984).
• Marvin Camras (ed.). Magnetic Tape Recording (New York: Van Nostrand Reinhold, 1985). ISBN 0442217749
• Eric D. Daniel, C. Dennis Mee, Mark H. Clark. Magnetic Recording: The First 100 Years, (New York: The Institute of Electrical and Electronics Engineers, 1999).
• International standard IEC 60094-7: Magnetic tape sound recording and reproducing systems. Part 7: Cassette for commercial tape records and domestic use. International Electrotechnical Commission, Geneva. (Also published as British Standard BS 6288-7:1994.)

External links

• Images of hundreds of different blank cassette styles
• Analog audio tape cassette nostalgia website
• Apple's iPod VS the Cassette Tape

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