What tape decks are
In general, a tape recorder, tape deck, or tape machine is any device that records a fluctuating signal by moving a strip of magnetic tape across a tape head, which is a strong electromagnet. Current flowing in the coils of the electromagnet cause the magnetic material on the tape to align in a manner proportional to the original signal. The signal can be reproduced by running the tape back across the tape head, where the reverse process occurs - the magnetic imprint on the tape induces a small current in the read head which approximates the original signal. This is then amplified for playback. Many tape recorders are capable of recording and playing back at once by means of separate record and playback heads in line or combined in one unit.
The storage of an analogue signal on tape works well, but is not perfect. In particular, the granular nature of the magnetic material adds noise to the signal, which is usually heard as tape hiss. Also, the magnetic characteristics of tape are not linear, they exhibit a characteristic hysteresis curve. The curvature causes unwanted distortion of the signal. Some of this distortion is overcome by using an inaudible high-frequency AC bias signal when recording, though the amount of bias needs careful adjustment for best results. Different tape material requires differing amounts of bias, whics is why most recorders have a switch to select this (or switch automatically). Additionally, systems such as Dolby B and Dolby HX-Pro have been devised to ameliorate some of the noise and distortion problems.
There are a wide variety of tape recorders in existence, from small hand held devices to large multitrack machines.
An important use of tape recorders is the recording of video. Video cassette recorders differ subtantially from audio recorders because of the use of a rotating magnetic head that uses a helical scan of the tape medium. Helical scan is used to allow for faster movement of the tape surface over the head.
While they are primarily used for sound recording, tape machines were also important for data storage before the advent of floppy disks and CDs, and are still used today, although primarily to provide an offline backup to hard disk drives.
The capstan is analogous to a rack and pinion arrangement found in gear systems.
Compact audio cassette
The compact audio cassette audio storage medium was introduced by Philips in 1963. It consists of a length of magnetic tape from BASF inside a protective plastic shell. Four tracks are available on the tape, giving two stereo tracks Ã¢Â€Â“ 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's backing. 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.
The cassette was a massive step forward in convenience from reel-to-reel audio tape 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. This permitted monaural cassette players to play stereo recordings in a highly-compatible "summed" form 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 Â¼ inch (6.35 mm) wide, each stereo track being 1/16 inch (1.5875 mm) wide, and running at either 3Â¾ or 7Â½ inches per second (95.25 or 190.5 mm/s). Some machines did use 17/8 inches per second (47.625 mm/s) but the quality was poor.
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). Some vendors were 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. There was also a C-100, which could accommodate a 50 minute album on each side Ã¢Â€Â“ a possible factor in its withdrawal.
The cassette had originally been intended for use in dictation machines, but quickly became a medium for distributing prerecorded music Ã¢Â€Â“ particularly through Philips's record company, PolyGram Ã¢Â€Â“ 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 (unauthorized concert recordings) for sale or trade.
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 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.
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 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.
Technical development of the cassette effectively ceased when digital recordable media such as DAT and MiniDisc were introduced in 1992. Philips attempted to introduce the Digital Compact Cassette Ã¢Â€Â“ a DAT-like tape in the same form factor Ã¢Â€Â“ 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.