Compact Cassette
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The Compact Cassette logo inspired that of the Compact Disc two decades later. |
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Typical 60-minute Compact Cassette. |
The
Compact Cassette, often referred to as
audio cassette,
cassette tape, or simply
cassette, is the most successful
magnetic tape sound recording format. It consists of two miniature
reels, between which an
oxide-coated plastic tape, or
magnetic tape, is passed and wound. These reels and attendant parts are held inside a protective plastic shell. Although originally intended as a medium for dictation, improvements in fidelity led it to supplant
reel-to-reel tape recording in most applications. Between the 1970s and early 1990s, the cassette was one of the two most common formats for prerecorded music, alongside the
LP and later the
Compact Disc.
Two
monophonic or four paired
stereo audio tracks are available on the tape; one monophonic track or stereo pair is 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 compact audio cassette medium for
audio storage was introduced in Europe by
Philips in
1963, and in the
U.S. in 1964, under the
trademark 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 (1979), with cassette sales overtaking those of
LPs. (Total vinyl record sales remained higher due to greater sales of singles, although cassette singles achieved popularity for a period in the
1990s).
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.
Introduction of music cassettes
The mass production of compact audio cassettes began in
1964 in
Hanover,
Germany. Prerecorded music cassettes (also known as
Musicassettes;
MC for short) were launched in Europe in late 1965. Musicassettes were introduced to the U.S. in September 1966 by The Mercury Record Company, a U.S. affiliate of Philips. The initial range consisted of 49 titles
[Electronics World magazine, November 1966].
However, the system had been initially designed for dictation and portable use, with the audio quality of early players 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 (CrO
2) tape by the
Advent Corporation resulted in the format being taken more seriously for musical use.
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 (1
7⁄
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).
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Although cassette-shells can vary widely in external appearance (the lower two are more recent in style), they are all internally similar. |
Cassette types
The original magnetic material was based on gamma ferric oxide (Fe
2O
3). Circa 1970,
3M Company developed a cobalt
volume-doping process combined with a double-coating technique to enhance overall tape output levels . This product was marketed as "High Energy" under its Scotch brand of recording tapes.
At about the same time
chromium dioxide (CrO
2) was introduced by
BASF, and then coatings using
magnetite (Fe
3O
4) such as
TDK's Audua were produced in an attempt to approach the sound quality of
vinyl records.
Cobalt-
adsorbed iron oxide (Avilyn) was introduced by TDK in 1974 and proved very successful. Finally pure metal particles (as opposed to oxide formulations) were introduced in 1979 by 3M under the tradename Metafine. The tape coating on most Cassettes sold today as either "Normal" or "Chrome" consist of Ferric Oxide and Cobalt mixed in varying ratios (and using various processes) there are very few cassettes on the market that use a pure (CrO
2) coating.
These each had different
bias and
equalization requirements requiring specialized settings. The most common, iron oxide tapes (defined by an
IEC standard as "Type I"), use 120
µS playback equalization, while chrome and cobalt-adsorbed tapes (IEC Type II) require 70 µS playback equalization. The record equalisations were also different (and had a much longer time constant).
Sony tried a dual layer tape with both ferric oxide and chrome dioxide known as 'ferrichrome' (FeCr) (IEC Type III) but these were only available for a short time in the 1970s. Metal Cassettes (IEC Type IV), also use 70 µS playback 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 playback equalisation but this idea only really caught on for commercial pre-recorded cassettes.
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Notches on the top surface of the audio cassette indicate its type. The top cassette, with only write protect notches (here covered by write protect tabs), is a Type I. The next cassette down, with additional notches adjacent to the write protect notch, is a Type II. The bottom two cassettes, featuring the Type II notches plus an additional pair in the middle of the cassette are type IV (metal); note the removal of the write-protect plastic tabs on the second of these. |
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.
Playback length
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 (not to mention "print through" echo). 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, C105 and C110. At least one company,
Sanyo included a complimentary blank C12 cassette with its portable cassette recorders in the early 1980s. 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.
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Inside a cassette. The tape is pressed into close contact with the head by the pressure pad; guide rollers help keep the tape in the correct position. Smooth running is assisted by a slippery liner between the reels and the shell - here the liner is transparent. The magnetic shield reduces pickup of stray signals by the heads of the player. |
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.
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 The Philips Record Company (and subsidiary labels Mercury and Philips in the U.S.) Starting in 1979,
Sony's
Walkman helped the format become widely used and popular.
As of 2006, 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 compansion (compression of the signal during recording and equal & opposite expansion of the signal during playback) which yields increased
dynamic range by lowering the noise level and increasing the maximum signal level before distortion occurs. 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 tape concerts (
unauthorized or authorized) for sale or trade, a practice tacitly or overtly encouraged by many bands with a more counterculture bent such as the
Grateful Dead. Blank compact cassettes also were an invaluable tool to spread the music of unsigned acts, especially within
Tape trading networks.
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. Most
home computers of the late
1970s and early
1980s could use cassettes for data storage as a cheaper alternative to
floppy disks. Even the first version of the
IBM PC of 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.
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 decline, with few retailers stocking them because they are no longer issued by the major music labels. Cassette
Music Tapes are now considered as
Collector's Items.
However,
as of 2006, blank cassettes are still being produced and are sold at many retail stores, and facilities for cassette duplication remain available. Cassette recorders and players are gradually becoming more scarce, but are still widely available.
Despite the wide availability of higher-fidelity media, they also remain popular for specific applications, including:
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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. While 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; lower fidelity is generally not a drawback for such content. While most publishers sell CD audiobooks nowadays, they usually also 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 likely to become increasingly marginalised as time goes on.
As of 2006 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. Most 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.
The word "cassette" is
French in origin, so it was acceptable to the
Académie française. 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/).
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Cassette culture*
Cassette single ("cassingle")
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Digital cassettes*
Elcaset*
Electronic journalism*
List of audio formats*
Microcassette*
Minicassette*
Mix tape*
PXL-2000 - A toy
camcorder that used compact audio cassettes to store video.
*Leonard Copland/Robert Johns. "The Tape Cartridge Comes Of Age",
Electronics World (November, 1966).
*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).
*
Collectible Cassette Tapes*
Vintage Cassette Decks A collection of Vintage cassette decks of all brands.
