 | This article includes a list of general references, but it lacks sufficient corresponding inline citations .(December 2009) |
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.
Print-through is a category of noise caused by contact transfer of signal patterns from one layer of tape to another after it is wound onto a reel.
Print-through can take two forms:
The former is unstable over time and can be easily erased by rewinding a tape and letting it sit so that the patterns formed by the contact of upper and lower layers begin to erase each other and form new patterns with the repositioning of upper/lower layers after rewinding. This type of contact printing begins immediately after a recording and increases over time at a rate dependent on the temperature of the storage conditions. Depending on tape formulation and type, a maximum level will be reached after a certain length of time, if it is not further disturbed physically or magnetically.
The audibility of print noise caused by contact printing depends on a number of factors:
Tape speed is a factor because of the shift in wavelengths. For example, the strongest print signal on a C-60 cassette running at 1.875 inches per second (4.76 cm/s) is about 426 Hz (605 Hz for a C-90), while an open-reel tape recorded at 7.5 inches per second (19 cm/s) would have its strongest signal at 630 Hz if the tape were a professional tape with a 1.5 mils (38 μm) base film or 852 Hz if the tape were a consumer version with a base film of 1.0 mil (25 μm) thickness.
The cause of print-through is due to an imbalance of magnetic and thermal energy in the magnetic particle. Once the magnetic energy is only 25 times greater than the thermal energy, the particle becomes unstable enough to be influenced by flux energy from the layer above or below the tape. The amount of magnetic energy depends on the coercivity of the particles, their shapes (long, thin particles make stronger "magnets"), the ratio of ideally shaped particles to defective particles, and their crystalline structures. Metal particles, although very small, have very high values of coercivity and are the most resistant to print-through effects because their magnetic energy is seldom challenged by thermal energy. Particles fractured by excessive milling prior to coating will increase levels of print depending on their ratio compared to their well-formed neighboring particles.
Anhysteretic print signals are almost as strong as intentionally recorded signals and are much more difficult to erase. This type of print noise is relatively rare because users are typically careful about accidentally exposing recordings to strong magnetic fields, and the magnetic influence of such fields decreases with distance.
Digital tapes can also be affected by contact print effects in a phenomenon known as "bit-shift" when upper or lower layers of tape cause a middle layer to alter the pulses recorded to represent binary information.
Since analog video is recorded by frequency-modulation of the video signal, the FM capture effect shields the signal against this noise; however, the linear audio and (depending on format) chrominance signals of a video cassette may have some print effects.
While print-through is a form of unwanted noise, contact printing was used deliberately for high-speed recording (duplication, high speed en masse copying) of video tape, instead of having to record thousands of tapes on thousands of VCRs at normal playback speed, or recording the source material repeatedly in real time to large reels (without end caps) of tape (called pancakes) over 48 hours long to be inserted into cassettes. [2] DuPont [3] in conjunction with Otari [4] invented a form of thermal magnetic duplication ("TMD") by which a high-coercivity metal mother master tape was brought into direct contact with a chromium dioxide copy (slave) tape. The coercivity of the mother tape is higher than that of the copy tape, so when the copy tape is heated and brought into contact with the mother tape, the copy tape gets a mirror image of the signal on the mother tape without the mother tape losing its signal. The recording on the mother tape was a mirror image of a valid video signal. Immediately before the copy tape came into contact with the mother tape, a focused laser beam heated it to its Curie point at which its value of coercivity dropped to very low values so that it picked up a near perfect copy of the mother tape as it cooled. [5] [6] The mother tape was made using a special reel to reel video tape recorder called a mirror master recorder [7] and was held inside the machine in an endless loop. This system could achieve speeds of up to 300 times playback speed in NTSC VHS SP mode, 900 times in VHS EP mode and 428 times in PAL/SECAM tapes. [8]
Sony developed a system known as "Sprinter" that used a similar mother master tape forced into close contact with any blank copy tape using compressed air and run across a rotating transfer head in which a weak AC high frequency sine wave is used to transfer the information anhysteretically to the copy tape with minimal erasure of the mother tape on each pass. The sprinter does not use a laser to heat the copy tape which saves on power consumption. The transfer head may have a vacuum cleaner to reduce dropout caused by dust. This system was used to quickly duplicate VHS tapes at speeds of up to 240 times faster than playback speed for NTSC and 342 times for PAL/SECAM video signals without having to use expensive chrome dioxide tape; the tape was fed into the sprinter at a speed of 8 meters per second. The mother tape was enclosed in a space (not in a reel, but rather in an endless loop) in the Sprinter; this was made possible by a horizontal vibrating tape feed system where the edge of the endless loop tape sits in a table that diagonally vibrates using vibration generated by piezoelectric elements and amplified using mechanical oscillation, causing the tape in the table to move forward. The copy tape was unwound, recorded using the mother tape, then wound onto large reels (called pancakes) containing enough tape for several VHS cassettes. The mother tape had a coercivity three times that of normal VHS tape and was made by recording onto it using a special reel to reel video tape recorder called a mirror mother VTR using video from a D-2 (video), Type B videotape or Type C videotape master source tape. The video tape recorder had a sapphire blade to clean the surface of the mother tape, reducing dropout caused by dust. Sprinter mother tapes did suffer enough loss that they had to be replaced after a number of passes. [9] The master had to be replaced every 1000 copies. This form of high-speed recording was very cost effective when recording in the EP (extra long play) mode because it was three times faster than recording in SP (standard play) mode while real-time recording took the same amount of time whether in EP mode that used less tape or SP mode that used a greater amount of tape. High-speed video recording of EP video produced far more consistent results than real-time recording at the slowest VHS speed. After duplication, the copy tape was loaded into video tape loaders that wound the tape into empty VHS cassette shells that contained only leader tape. [10]
Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnetic tape could with relative ease record and playback audio, visual, and binary computer data.
VHS is a standard for consumer-level analog video recording on tape cassettes.
The Compact Cassette, also commonly called a cassette tape, audio cassette, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. Invented by Lou Ottens and his team at the Dutch company Philips in 1963, Compact Cassettes come in two forms, either already containing content as a prerecorded cassette (Musicassette), or as a fully recordable "blank" cassette. Both forms have two sides and are reversible by the user. Although other tape cassette formats have also existed—for example the Microcassette—the generic term cassette tape is normally always used to refer to the Compact Cassette because of its ubiquity.
Digital Audio Tape is a signal recording and playback medium developed by Sony and introduced in 1987. In appearance it is similar to a Compact Cassette, using 3.81 mm / 0.15" magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm × 54 mm × 10.5 mm. The recording is digital rather than analog. DAT can record at sampling rates equal to, as well as higher and lower than a CD at 16 bits quantization. If a comparable digital source is copied without returning to the analogue domain, then the DAT will produce an exact clone, unlike other digital media such as Digital Compact Cassette or non-Hi-MD MiniDisc, both of which use a lossy data reduction system.
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.
Videotape is magnetic tape used for storing video and usually sound in addition. Information stored can be in the form of either an analog or digital signal. Videotape is used in both video tape recorders (VTRs) and, more commonly, videocassette recorders (VCRs) and camcorders. Videotapes have also been used for storing scientific or medical data, such as the data produced by an electrocardiogram.
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 mini 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.
S-VHS (スーパー・ヴィエイチエス), the common initialism for Super VHS, is an improved version of the VHS standard for consumer-level video recording. Victor Company of Japan introduced S-VHS in Japan in April 1987, with their JVC-branded HR-S7000 VCR, and in certain overseas markets soon afterward. By the end of 1987, the first S-VHS VCR models from other competitors included Hitachi VT-2700A, Mitsubishi HS-423UR, Panasonic PV-S4764, RCA VPT-695HF, and Toshiba SV-950.
Betamax is a consumer-level analog recording and cassette format of magnetic tape for video, commonly known as a video cassette recorder. It was developed by Sony and was released in Japan on May 10, 1975, followed by the US in November of the same year.
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.
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.
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 8mm video format refers informally to three related videocassette formats. These are the original Video8 format and its improved successor Hi8, as well as a more recent digital recording format known as Digital8. Their user base consisted mainly of amateur camcorder users, although they also saw important use in the professional television production field.
VHS-C is the compact VHS videocassette format, introduced by Victor Company of Japan (JVC) in 1982, and used primarily for consumer-grade compact analog recording camcorders. The format is based on the same video tape as is used in VHS, and can be played back in a standard VHS VCR with an adapter. Though quite inexpensive, the format is largely obsolete even as a consumer standard and has been replaced in the marketplace by digital video formats, which have smaller form factors.
A loop bin duplicator is a specialized audio tape machine used in the duplication of pre-recorded audio cassettes and 8-track cartridges.
Chromium dioxide or chromium(IV) oxide is an inorganic compound with the formula CrO2. It is a black synthetic magnetic solid. It once was widely used in magnetic tape emulsion. With the increasing popularity of CDs and DVDs, the use of chromium(IV) oxide has declined. However, it is still used in data tape applications for enterprise-class storage systems. It is still considered by many oxide and tape manufacturers to have been one of the best magnetic recording particulates ever invented.
V-Cord is an analog recording videocassette format developed and released by Sanyo. V-Cord was released in 1974, and could record 60 minutes on a cassette. V-Cord II, released in 1976, could record 120 minutes on a V-Cord II cassette.
A videocassette recorder (VCR) or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other source on a removable, magnetic tape videocassette, and can play back the recording. Use of a VCR to record a television program to play back at a more convenient time is commonly referred to as timeshifting. VCRs can also play back prerecorded tapes. In the 1980s and 1990s, prerecorded videotapes were widely available for purchase and rental, and blank tapes were sold to make recordings.
Audio compact cassettes use magnetic tape of three major types which differ in fundamental magnetic properties, the level of bias applied during recording, and the optimal time constant of replay equalization. Specifications of each type were set in 1979 by the International Electrotechnical Commission (IEC). By this time, Type I included pure gamma ferric oxide formulations, Type II included ferricobalt and chromium dioxide formulations, and Type IV included metal particle tapes—the best-performing, but also the most expensive. In the 1980s the lines between three types blurred. Panasonic developed evaporated metal tapes that could be made to match any of the three IEC types. Metal particle tapes migrated to Type II and Type I, ferricobalt formulations migrated to Type I. By the end of the decade performance of the best Type I ferricobalt tapes (superferrics) approached that of Type IV tapes; performance of entry-level Type I tapes gradually improved until the very end of compact cassette production.
In magnetic tape recording, adaptive biasing is the technique of continuously varying the bias current to a recording head in accordance with the level of high-frequency audio signals. With adaptive biasing, high levels of high-frequency audio signals cause a proportionate decrease in bias current using either feedforward or preferably a negative feedback control system. Compared with the use of fixed bias current, adaptive biasing provides a higher maximum output level and higher dynamic range at the upper end of the audible spectrum and to a lesser extent, mid-range frequencies. The effect of adaptive biasing is most pronounced in compact cassette and low-speed reel-to-reel media. The first commercial implementation, the feedforward system Dolby HX was developed by Dolby Laboratories by 1979 and was rejected by the industry. The subsequent negative-feedback system Dolby HX Pro was developed by Bang & Olufsen and marketed by Dolby, and became the de facto standard of the consumer high fidelity industry in the mid-1980s.
{{cite web}}: |last= has generic name (help){{cite web}}: |first= has generic name (help)