It has been suggested that Recording head be merged into this article. (Discuss) Proposed since October 2024.
Tape head assembly from a compact cassette deck. The compact cassette uses four tracks, two for each side; visible are two heads (the silver rectangles inside the black rectangle) for playing one side of the tape at a time.
A tape head is a type of transducer used in tape recorders to convert electrical signals to magnetic fluctuations and vice versa. They can also be used to read credit/debit/gift cards because the strip of magnetic tape on the back of a credit card stores data the same way that other magnetic tapes do. Cassettes, reel-to-reel tapes, 8-tracks, VHS tapes, and even floppy disks and early hard drive disks all use the same principle of physics to store and read back information. The medium is magnetized in a pattern. It then moves at a constant speed over an electromagnet. Since the moving tape is carrying a changing magnetic field with it, it induces a varying voltage across the head. That voltage can then be amplified and connected to speakers in the case of audio, or measured and sorted into ones and zeroes in the case of digital data.
The electromagnetic arrangement of a tape head is generally similar for all types, though the physical design varies considerably depending on the application - for example videocassette recorders (VCR) use rotating heads which implement a helical scan, whereas most audio recorders have fixed heads. A head consists of a core of magnetic material arranged into a doughnut shape or toroid, into which a very narrow gap has been let. This gap is filled with a diamagnetic material, such as gold.[citation needed] This forces the magnetic flux out of the gap into the magnetic tape medium more than air would, and also forces the magnetic flux out of the magnetic tape medium into the gap. The flux thus magnetises the tape or induces current in the coil at that point. A coil of wire wrapped around the core opposite the gap interfaces to the electrical side of the apparatus. The basic head design is fully reversible - a variable magnetic field at the gap will induce an electric current in the coil, and an electric current in the coil will induce a magnetic field at the gap.
Reversibility
While a head is reversible in principle, and very often in practice, there are desirable characteristics that differ between the playback and recording phases. One of these is the impedance of the coil - playback preferring a high impedance, and recording a low one. In the very best tape recorders, separate heads are used to avoid compromising these desirable characteristics. Having separate heads for recording and playback has other advantages, such as off-tape monitoring during recording, etc.
Head gap width
The width of the head gap is also critical - the narrower the gap, the better the head will be - a narrow gap gives much better transcription in the magnetic domain (which equals to more output with high frequency signals in the case with playback heads). The desirability for a narrow gap means that most practical heads are made by forming a narrow V-shaped groove in the back face of the core, and grinding away the front face until the V-groove is just breached. In this way, gaps of the order of micrometres are achievable.
A record head, on the other hand, has a gap typically six times larger than that of the replay head, this gives a larger flux to magnetise the tape. The ideal gap size in a cassette deck are; wide record head gap and narrow playback head. The larger gap does not affect frequency response because the 'image' is largely made by the trailing edge of the gap. A combined record/replay head has a compromise size gap typically three times that of a replay only head.
There are also negative aspects of narrow head gaps, particularly for magnetic recording. The narrower the head gap, the more bias signal must be used to maintain linearity of the signal on tape which in turn will reduce the high frequency headroom or SOL (Saturated Output Level), particularly with slower tape speeds. Manufacturers must find a compromise between intended tape speeds and head gaps for this reason.
Types
The physical design of a head depends on whether it is fixed or rotating. In either case, the face of the head where the gap is must be made hard wearing and highly smooth to avoid excessive head wear. It can also be seen that due to the construction method of the head gap, head wear will tend to widen the gap, reducing the head's performance over time. The vertical alignment of the heads (the azimuth) must also match between recording and playback for good fidelity, and the gap should be as close to exactly vertical as possible for highest frequency response. Most tape transport mechanisms will allow fine mechanical adjustment of the azimuth of the heads. Sometimes this can be achieved by automatic circuitry - the actual mechanical azimuth adjustment being carried out by taking advantage of the piezo effect of certain types of crystal material.
Rotating heads
Rotating play heads, as used in video recorders, digital audio tape and other applications, are used to achieve a high relative head/tape speed while maintaining a low overall tape transport speed. One or more transducers are mounted on a rotating drum set at an angle to the tape. The drum spins rapidly compared to the speed that the tape moves past it, so that the transducers describe a path of stripes across the tape, rather than linearly along it as a fixed head does. The wear characteristics of such helical scan heads are even more critical, and highly polished heads and tapes are required. The electrical signals of rotating heads are coupled either inductively or capacitively - there is no direct connection to the head coils.
Erase heads
Erase head
An erase head is constructed in a similar manner to a record or replay head, but has a much larger gap, or more frequently, two large gaps. The erase head is powered during recording from a high frequency source (usually the same oscillator that provides the AC bias). In some inexpensive cassette recorder designs, the erase head is a permanent magnet that is mechanically moved into contact with the moving tape only during recording. Permanent magnet erase heads are also sometimes used in machines that are equipped with DC bias.
Cross-field heads
Instead of feeding both the bias signal and the audio signal into the same recording head, a few brands of audio tape recorder, notably Tandberg, Akai and its US cousin Roberts, used a separate bias head on the opposite side of the tape from the recording head; this system was termed cross-field.
Head materials
Record and replay heads are traditionally made of soft iron (the softness is an essential requisite for good record and replay characteristics). This material features extremely good electro-acoustical properties, but wears away fairly rapidly with a consequent deterioration of performance. Some higher end recorders featured heads made from ferrite, which features excellent electro-acoustical properties while being a very hard material which resists wear. Its two main disadvantages are that it is brittle and easily damaged, and that it has a much higher noise output due to the Barkhausen effect. In more recent years, more exotic materials have appeared, some involving ceramics, which offer the best of both of the traditional materials.
Cleaning
With use the head will become dirty with loose tape shedding. Video head cleaner can be used to clean video, audio, erase, or control track heads.
Tape bias is the term for two techniques, AC bias and DC bias, that improve the fidelity of analogue tape recorders. DC bias is the addition of direct current to the audio signal that is being recorded. AC bias is the addition of an inaudible high-frequency signal to the audio signal. Most contemporary tape recorders use AC bias.
The VHS is a standard for consumer-level analog video recording on tape cassettes, introduced in 1976 by the Victor Company of Japan (JVC). It was the dominant home video format throughout the tape media period in the late 1970s, 1980s, and 1990s.
An audio tape recorder, also known as a tape deck, tape player or tape machine or simply a tape recorder, is a sound recording and reproduction device that records and plays back sounds usually using magnetic tape for storage. In its present-day form, it records a fluctuating signal by moving the tape across a tape head that polarizes the magnetic domains in the tape in proportion to the audio signal. Tape-recording devices include the reel-to-reel tape deck and the cassette deck, which uses a cassette for storage.
A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording. The first was Dolby A, a professional broadband noise reduction system for recording studios that was first demonstrated in 1965, but the best-known is Dolby B, a sliding band system for the consumer market, which helped make high fidelity practical on cassette tapes, which used a relatively noisy tape size and speed. It is common on high-fidelity stereo tape players and recorders to the present day, although Dolby has as of 2016 ceased licensing the technology for new cassette decks. Of the noise reduction systems, Dolby A and Dolby SR were developed for professional use. Dolby B, C, and S were designed for the consumer market. Aside from Dolby HX, all the Dolby variants work by companding: compressing the dynamic range of the sound during recording, and expanding it during playback.
A cassette deck is a type of tape machine for playing and recording audio cassettes that does not have a built-in power amplifier or speakers, and serves primarily as a transport. It can be a part of an automotive entertainment system, a part of a portable audio system or a part of a home component system. In the latter case, it is also called a component cassette deck or just a component deck.
Ampex Data Systems Corporation is an American electronics company founded in 1944 by Alexander M. Poniatoff as a spin-off of Dalmo-Victor. The name AMPEX is an acronym, created by its founder, which stands for Alexander M. Poniatoff Excellence. Ampex operates as Ampex Data Systems Corporation, a subsidiary of Delta Information Systems, and consists of two business units. The Silicon Valley unit, known internally as Ampex Data Systems (ADS), manufactures digital data storage systems capable of functioning in harsh environments. The Colorado Springs, Colorado, unit, referred to as Ampex Intelligent Systems (AIS), serves as a laboratory and hub for the company's line of industrial control systems, cyber security products and services and its artificial intelligence/machine learning technology.
Helical scan is a method of recording high-frequency signals on magnetic tape, used in open-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drives.
Reel-to-reel audio tape recording, also called open-reel recording, is magnetic tape audio recording in which the recording tape is spooled between reels. To prepare for use, the supply reel containing the tape is placed on a spindle or hub. The end of the tape is manually pulled from the reel, threaded through mechanical guides and over a tape head assembly, and attached by friction to the hub of the second, initially empty takeup reel. Reel-to-reel systems use tape that is 1⁄4, 1⁄2, 1, or 2 inches wide, which normally moves at 3+3⁄4, 7+1⁄2, 15 or 30 inches per second. Domestic consumer machines almost always used 1⁄4 inch (6.35 mm) or narrower tape and many offered slower speeds such as 1+7⁄8 inches per second (4.762 cm/s). All standard tape speeds are derived as a binary submultiple of 30 inches per second.
Betacam is a family of half-inch professional videocassette products developed by Sony in 1982. In colloquial use, Betacam singly is often used to refer to a Betacam camcorder, a Betacam tape, a Betacam video recorder or the format itself.
A video tape recorder (VTR) is a tape recorder designed to record and playback video and audio material from magnetic tape. The early VTRs were open-reel devices that record on individual reels of 2-inch-wide (5.08 cm) tape. They were used in television studios, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. Beginning in 1963, videotape machines made instant replay during televised sporting events possible. Improved formats, in which the tape was contained inside a videocassette, were introduced around 1969; the machines which play them are called videocassette recorders.
Print-through is a generally undesirable effect that arises in the use of magnetic tape for storing analog information, in particular music, caused by contact transfer of signal patterns from one layer of tape to another as it sits wound concentrically on a reel.
A recording head is the physical interface between a recording apparatus and a moving recording medium. Recording heads are generally classified according to the physical principle that allows them to impress their data upon their medium. A recording head is often mechanically paired with a playback head, which, though proximal to, is often discrete from the record head.
1-inch Type C Helical Scan or SMPTE C is a professional reel-to-reel analog recording helical scan videotape format co-developed and introduced by Ampex and Sony in 1976. It became the replacement in the professional video and broadcast television industries for the then-incumbent 2-inch quadruplex videotape open-reel format. Additionally, it replaced the unsuccessful type A format, also developed by Ampex, and primarily in mainland Europe, it supplemented the type B format, developed by the Fernseh division of Bosch.
1-inch Type B Helical Scan or SMPTE B is a reel-to-reel analog recording video tape format developed by the Bosch Fernseh division of Bosch in Germany in 1976. The magnetic tape format became the broadcasting standard in continental Europe, but adoption was limited in the United States and United Kingdom, where the Type C videotape format met with greater success.
Azimuth recording is the use of a variation in angle between two recording heads that are recording data so close together on magnetic tape that crosstalk would otherwise likely occur. Normally, the head is perpendicular to the movement of the tape, and this is considered zero degrees. However, if the heads are mounted at slightly different angles, destructive interference will occur at high frequencies when reading data recorded in the cross-talking channel but not in the channel that is intended to be read. At low frequencies relative to the maximum allowed by the head gap, however, this technique is ineffective. Thus one head is slanted slightly leftwards and the magnetic gap of the other head slanted slightly rightwards.
The history of sound recording - which has progressed in waves, driven by the invention and commercial introduction of new technologies — can be roughly divided into four main periods:
A control track is a track that runs along an outside edge of a standard analog videotape. The control track encodes a series of pulses, each pulse corresponding to the beginning of each frame. This allows the video tape player to synchronize its scan speed and tape speed to the speed of the recording. Thus, the recorded control track defines the speed of playback, and it is also what drives the relative counter clock that most VCRs have.
D6 HDTV VTR is SMPTE videocassette standard. A D6 VTR can record and playback HDTV video uncompressed. The only D6 VTR product is the Philips, now Thomson's Grass Valley's Media Recorder, model DCR 6024, also called the D6 Voodoo VTR. The VTR was a joint project between Philips Digital Video Systems of Germany and Toshiba in Japan. The tape deck module was designed and made by Philips in Weiterstadt, Germany, and the digital processor module designed and made by Toshiba. Since there is no data compression, after 20 tape copies of multi generations there is no noticeable loss of quality. As a very high-end, costly system about 70 were sold to high-end post houses from about 2000 to 2005. The VTR had a data record option. The data module could record and play back 2k DPX files at 6 frames per second over a HIPPI connection. The VTR came in a data only model, or with a switch module, so the record deck could be used for both video and data recording. The tape deck was also sold stand alone as a giga bit recorder to record and playback raw data. Toshiba made the video tape for the VTR. The high price of the video tape limited the use of the VTR.
EIAJ-1 was a standard for video tape recorders (VTRs) developed by the Electronic Industries Association of Japan with the cooperation and assistance of several Japanese electronics manufacturers in 1969. It was the first standardized format for industrial/non-broadcast VTRs using a helical scan system employing open reel tape. Previously, each manufacturer of machines in this market used a different proprietary format, with differing tape speeds, scanner drum diameters, bias frequencies, tracking head placement, and so on, although most used 1/2" wide tape. As a result, video tapes recorded on one make and/or model of VTR could only be interchanged with other machines using that specific format, hampering compatibility. For example, a reel of tape recorded on a Panasonic machine would not play on a Sony machine, and vice versa. The EIAJ-1 standard ended this incompatibility, giving those manufacturers a standardized format, interchangeable with almost all VTRs subsequently brought to market around that time. The format offered black-and-white video recording and playback on 1/2″ magnetic tape on a 7″ diameter open reel, with portable units using smaller 5″ diameter reels.
The Nakamichi Dragon is an audio cassette deck that was introduced by Nakamichi in 1982 and marketed until 1994. The Dragon was the first Nakamichi model with bidirectional replay capability and the world's first production tape recorder with an automatic azimuth correction system; this feature, which was invented by Philips engineers and improved by Niro Nakamichi, continuously adjusts the azimuth of the replay head to minimize apparent head skew and correctly reproduce the treble signal present on the tape. The system allows the correct reproduction of mechanically skewed cassettes and recordings made on misaligned decks. Apart from the Dragon, similar systems have only been used in the Nakamichi TD-1200 car cassette player and the Marantz SD-930 cassette deck.
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