A tape recorder is an audio recorder for analog audio recording on tape material . The latter consists of thin plastic as a carrier material, which is coated with a magnetizable layer with iron , iron oxide and / or chromium oxide crystals. Analog tape recorders and the related cassette recorders were practically completely displaced from the market by the triumph of digital technology in entertainment and studio electronics.
Structure and technology
As standard, the supply reel with the tape supply is located on the left, the head carrier with the tape heads and the capstan in the middle and the take-up reel on the right (see diagram on the right). In the professional sector, open belt discs are also used, the AEG spool core (so-called bobby) or the NAB ring serve as the winding body.
Erase head and tape head
Two tape heads are used for recording . First, the tape runs over a pulley past the erase head (LK), which has a relatively wide head gap and is fed from the erase generator at high frequencies far beyond the audible frequency - usually over 80 kHz . A quality-reducing direct current erase head or fixed magnet is rather rare in tape recorders. The actual recording takes place with a speaking head (SK), which has a slightly wider head gap than the hearing head (HK) in order to allow a sufficient flow of the magnetizable material and thus sufficient level and signal to noise ratio . The low frequency to be recorded is modulated with the high frequency from the erase generator in order to avoid hysteresis effects, the so-called premagnetization . Usually the premagnetization is mixed in at the output of the recording amplifier, with Tandberg and Akai an extra sound head on the back of the tape opposite the recording head added the premagnetization (Crossfield technique). A headset is used for playback, which should have as narrow a head gap as possible in order to achieve the highest possible cutoff frequency. In the case of cheaper devices, only a single combination head is used as both a listening and speaking head, which is then designed according to a compromise for both requirements. Merging the listening and speaking heads makes it impossible to check the current recording directly.
Posterior ligament control
Listening to the recording that has just been magnetized onto the tape at the recording head by the following playback head is called the rear tape check . This requires more complex electronics that provide separate circuits for recording and playback, but also enable so-called "multiplay" or an echo effect , such as echo effects , through internal feedback of the playback signal into the recording channel . B. in the “Royal de luxe” from Uher . Combination head devices use the same electronics, which have to be switched as recording amplifiers or playback amplifiers, with the corresponding equalization characteristics and high frequency traps, because the erasing oscillator must also deliver the premagnetization to the recording head without disturbing the recording amplifier. It is obvious that a tape recorder with an erase oscillator and recording amplifier, erase head and recording head (with a 7 micrometer gap width) can be consistently optimized for recording, while a separate playback head (2 micrometers gap width) with an optimized playback amplifier delivers the best playback quality. Compared to the combi-head device, more effort is required to adjust the audio head, but the higher and lower-distortion magnetization of the tape, the better frequency response and the more precise phase position (reference for the recording head is the rear gap edge, for the playback head the gap center) rather meet high HiFi requirements.
In practice, the head gap is not an air gap, but an anti-magnetic metal foil of a defined thickness.
In Uher's “Royal de luxe” there was another sound head which enabled the setting of slide presentations with manually controlled single impulses or Super 8 films using the standard sound method . This so-called slide head used its own area of the tape as a pulse track for recording the audio frequency pulses. (see also clock head )
The actual belt drive does not take place via the belt disk, as this would lead to fluctuations in speed given the constant changes in the diameter of the belt laps. The constant tape speed is ensured by a vertical, precision-made steel shaft in close proximity to the tape heads, which has a precisely defined diameter and rotates at a highly constant speed. This wave is called a capstan or capstan, it is often chemically roughened to keep the slippage during tape transport low. The tape is pressed against this by a spring-loaded rubber roller ( pressure roller ). The tape plates are then only there to unwind the tape material with little resistance and to wind it up with a slight tension on the other side. In the case of inexpensive devices, this is usually done by mechanical slip clutches , the drive of which is derived from the capstan motor via intermediate gears. In the case of (semi) professional devices (e.g. Revox ), three motors are used, two of which are responsible for the torque of the two winding plates and the third for driving the capstan shaft. If the motor shaft directly carries the winding disc or functions as a capstan and the respective motor is electronically controlled, the mechanical structure can be simplified, while at the same time increasing reliability, durability, freedom from maintenance and sound quality.
The tape calming roller used for the first time by Telefunken near the recording head dampens longitudinal tape vibrations which, as frequency modulation components, would worsen the reproduction with modulation noise, perceived as roughness. This task can be performed by a ball bearing in the left deflecting mandrel (Revox) or a role in the tape guide (ASC), which simultaneously ensures that the head mirror is optimally wrapped between the recording and playback heads. The next higher belt speed shows fewer longitudinal vibrations, which in addition to a better frequency response is reflected in increased clarity and transparency. In addition, there is an improved controllability of the high frequency components at high belt speeds. There is a good reason why high quality tape devices use high speeds and half track for stereo. With quarter track you can hear the opposite track at 19 or 38 cm / s in the bass range. Quarter track has 3 lawn tracks, half track only one, the resulting larger usable track width improves the signal-to-noise ratio and also the dropout safety during recording, where good tape-head contact is more important than during playback. In practice, unfortunately, often played tapes are less suitable for new recordings, deformed tape edges and tape abrasion prevent the necessary head contact for even magnetization.
The tape speed of reel tape recorders is now 9.5 cm / s or multiple double or half of it (19, 38, 76 cm / s, 4.75 cm / s). The value 4.75 cm / s is also used for audio cassettes . Video cassettes of the VHS system run at standard speed under PAL about half as fast (2,339 cm / s), but the actual tape-to-head speed is many times greater.
Each belt speed has its special optimal emphasis . A standardized time constant is part of this change in the frequency response . In this case, be raised when taking high frequencies (or predistortion pre-emphasis ) which, when the reproduction by the equalization ( de-emphasis are lowered again). With this procedure, the tape noise is reduced, characteristic frequency response behavior of the tape materials is corrected and the control limit is optimized, because in music not all frequencies have identical maximum amplitudes, let alone suitable for the tape saturation.
Noise reduction systems such as Dolby-A in the professional sector, dbx or Dolby-B in the home hi-fi sector can significantly improve the signal-to-noise ratio . In addition to a linear frequency response of the tape recorder between recording and playback, they usually also require a standardization of the level , because their level-dependent mode of operation is optimized for level control at high levels and for noise reduction at low levels. Dolby-B, a level-mismatched to frequency response errors leads, as is a level loss by storage as well as the onset time loss of brilliance .
After more theoretical preparatory work by Oberlin Smith (1878/1888) and the first, not fully marketable devices by Valdemar Poulsen , steel wire magnetic sound devices mainly for dictation purposes and steel tape devices for broadcasting applications appeared at the end of the 1920s ( Curt Stille , Semi Joseph Begun ). After Fritz Pfleumer proposed a tape coated with magnetizable steel powder as a sound storage device in 1928, AEG introduced the magnetophone in 1935 , which worked with a cellulose acetate tape supplied by the IG Farbenindustrie Aktiengesellschaft . Since 1939 it was coated with the ferromagnetic iron oxide (γ) - Fe 2 O 3 . The magnetophone tape, initially self-supporting on winding cores, was 6.5 mm wide; Since around 1948, 6.3 mm has been the standard international bandwidth. These first devices were later called full-track devices because the entire width of the tape is used for recording (= track) in one direction. The belt speed is first 100 cm / s, then 77 cm / s (Germany) or 76.2 cm / s (international, corresponding to 30 inches / s), later 38.1 cm / s; this was followed by further halving of the tape feed down to 2.38 cm / s. Amateur and semi-professional devices almost without exception used 19 cm / s or, with a slight loss of quality, 9.5 cm / s; in the professional studio sector (radio and recording studios), the standard of 38.1 cm / s was usually maintained. In the case of professional special devices such as flight recorders , which primarily depend on a long running time, the belt speeds are sometimes even lower.
In the late 1940s there were the first half-track devices that basically worked with tape wound on reels. In the first pass, a bit less than half the width of the tape is recorded. Then, at the end of the tape at the latest, the reels are swapped ( turned ) and in a further pass the second track is recorded in the opposite direction. This doubles the playing time with the same tape length.
From the beginning of the 1950s, an increasing number of manufacturers brought tape recorders for the home market onto the market, with more and more technical possibilities and increasing quality:
- Track positions : Home tape recorders were initially manufactured using half-track technology. Their track position - the upper half of the bandwidth is recorded in the first run - was not standardized until 1956, which is why not all tapes recorded with devices from different manufacturers were compatible until then. Quarter-track devices did not exist until the late 1950s. Tapes recorded in half- and quarter-track technology were not compatible (half-track tapes could be played on quarter-track devices with quality restrictions). Occasionally, devices with exchangeable head carriers (the component that houses the transducers necessary for erasing, recording and playback) for half and quarter track were also offered. The change required only a few simple steps. Half-track tape recorders with an additional playback head for quarter-track recordings were seldom found.
- Stereophony : Devices with two-channel recording for spatial sound reproduction also only came out at the end of the 1950s.
- Multiple tape speeds : Initially, the 19.05 cm / s tape speed was the standard for home tape recorders. But then the speed was halved several times - in favor of the running time and at the expense of the playback quality: 9.53 cm / s, 4.76 cm / s up to 2.38 cm / s. The belt speed could be switched for several devices in the upper price and quality classes.
In 1955, Max Knobloch was enthusiastic in his book Der Tonband-Amateur (according to his own statement the first ever for this target group): “The magnetic tape recorders fulfill the old dream of humans, to record language and music and all acoustic expressions of the environment themselves and to play them back as often as desired to be able to keep. The tape amateur joined the photo amateur. Its technical aids are by no means more expensive than high-quality cameras; the versatility of his work gives him at least the same level of joy and satisfaction. ”For many private interested parties with average incomes, however, home devices remained unaffordable for the time being, or at least a long-term savings goal.
A little later, multi-track tape recorders were developed for the professional sector - first 4-track, then 8-track devices with a bandwidth of 1 inch (1 inch = 25.4 mm), in the further development up to 24 tracks on 2 inch wide tape (50.8 mm). This makes it possible to record 24 individual sound sources simultaneously or one after the other; each sound source is assigned to a track during the original recording. This means that mixing can be done later and repeated until you are satisfied. 32-track devices for 50.8 mm tape were delivered less often. Up to 48 tracks on ½-inch tape (12.7 mm) were only made possible by the digital recording technology with professional magnetic tape digital recorders, which was only used for a few years. Reel tape recorders are rarely used today, they can still be found occasionally in the professional sector, especially in recording studios; but even there they have been almost completely displaced by digital processes.
In the 1960s, transistor technology made reel tape recorders more compact, lighter and cheaper, and home tape recorders experienced a sales boom. “Hot on the heels of the drill, the spread of the tape is striving to reach its peak in the 1960s” (Deutschlandfunk). According to estimates, the inventory of tape recorders in the Federal Republic of Germany at the end of 1962 was around 5 to 6 million devices; the saturation level was 25% of households. The tape was "one of the most important media for information and documentation, a cultural-political factor of the first order (according to a statement by the Federal Council on the occasion of the rejection of an obligation to pay remuneration for private tape recordings)." Over 50 models were made by almost a dozen manufacturers in the Federal Republic of Germany, including West Berlin offered at prices from DM 250 to DM 2000; The main buyers were the 15 to 25 year olds, followed by the 25 to 35 year olds. The popularity and economic importance of the home tape recorder increased continuously. In 1965, Grundig, Philips and Telefunken agreed that the tape recorder sector was the most expansive branch of their production.
In the early 1970s, reel home tape recorders passed their peak, and the cassette recorders with compact cassettes (audio cassettes) developed and introduced in the previous decade conquered the market. They are, in turn, considerably smaller than reel tape recorders, more convenient to use and "foolproof" because of the tape protected by a housing. In addition, a variety of pre-recorded music cassettes (MusiCassette) was offered. The significantly narrower tape material initially only allowed a reduced sound quality, although the compact cassette was intended for music playback from the start. After occasional use for dictation purposes, even smaller cassette systems with sufficient verbosity prevailed. That changed quickly, especially when CrO 2 tape material (later also cobalt-doped iron oxide) was developed from 1970 , which also made hi-fi quality possible. Electronic noise reduction systems (Dolby, HighCom (Telefunken)) again noticeably increased the sound quality. New tape heads were also developed that had a very long service life (glass ferrite head). Thus the cassette recorders slowly replaced the reel tape recorders outside of professional applications.
The introduction of recorders with a radio part, the radio recorders , led to a widespread use, especially in youth culture. In the 1970s and 1980s, relatively large devices were built with two cassette decks (for quick transfer to another cassette) and powerful stereo amplifiers. The worldwide spread of the compact cassette system culminated in the battery-operated player type, the Walkman . A fundamental weakness of the compact cassette was that the tape guidance - and thus the correct reproduction of the higher pitches - depended on the injection-molded precision of the cassette housing. Further handling problems, e.g. For example, frequent " tape salad " due to uneven tape travel, poorly running tape material or subsequent loss of quality of the recordings due to unintentional magnetization etc. showed the limits of the technology. New technologies, especially the compact disc (CD) developed in the early 1980s , ultimately led to its displacement. Initially, the CD served as a high-quality supplement to the audio cassette - CD players were also built into radio recorders. Many radio recorders also had built-in microphones - in Asia, for example, karaoke recordings are very popular.
Today, tape or cassette devices are used less and less. Self-burned and recorded CDs or DVDs as well as computer hard drives (especially with MP3 music files) penetrated their domain .
The German special way
Already at the Reichs-Rundfunk-Gesellschaft - thus also in "affiliated" Austria - and then later in the ARD area , it was - and is still today in ARD sound archives - common to use tape machines in so-called "German shift positions" . There the tape heads are on the opposite side, so the tape is wound up with the magnetic side facing out. When exchanging tapes with other countries - or private studios - in the first few years it was always necessary to point out the layer position and thus also the track position, because this is reversed when the tape is scanned with the layer side inwards and the tapes to Play to be wrapped. The standard was later corrected to the effect that the lower head system belongs to the left channel on machines that worked in German shift positions. (This standard was also used in the GDR for a short time after the war, when the international shift was adopted.) As a result, the situation was correct even when the tape was played on devices for the international shift.
The tracks in the ARD standard were also a bit wider (2.75 mm) and the separating track was therefore narrower, but this does not matter when playing on devices with slightly narrower head systems.
After 1945 Austria only worked with the “international shift position”, Switzerland also used this. Which layer position is easier when working with tapes has always been controversial. The so-called pre-echoes caused by the copy effect , which were often very annoying with old tapes, were avoided - or at least reduced - by the German layering . With the pre-echo, loud passages sound once or several times with increasing level before the actual tone, because the tape has then become magnetized. The magnetized tape acts like a magnet here and influences the windings underneath, especially if the tapes are stored hard-wound. Of course, pre- and post-echoes occur in both layers, since the magnetic field has no preferred direction. However, the pre-echo is subjectively more annoying because it occurs unexpectedly. In this respect, it has always been an advantage of the German layer position that when the tape is rewound, the pre-echo remains 2 ... 3 dB lower than the post-echo. In order to enjoy the same advantage with international shifts, such tapes are stored "tail out" (pre-wound).
When, with the advent of the CD, more and more good recordings from foreign archives were processed into CDs in Germany, it happened - and still happens - that no attention was paid to the assignment of the tracks to the stereo channels and the channels were swapped. An example of this is the recording of Anton Bruckner's 9th Symphony with the Leningrad Philharmonic under Yevgeny Mrawinsky , which was released in this way in 1987/1993.
The Revox company always produced studio machines in the ARD standard for ARD.
Major manufacturers of tape recorders
- Bang & Olufsen
- Loewe Opta
- Revox / Studer
- Teac / Tascam
- Telefunken (see also Magnetophon )
- Unitra (Polish devices)
- Friedrich Engel, Gerhard Kuper, Frank Bell, Wulf Münzner: Time layers: Magnetic tape technology as a cultural medium. Inventor biographies and inventions . 4th edition. Polzer Media Group, Potsdam 2020 (e-book, PDF).
- Frieder Butzmann : What was not in the operating instructions: Observations during the development and use of sound recording and playback systems in the 20th century. In. Technikgeschichte, Vol. 61 (1994), H. 1, pp. 35-57.
- Device catalog magnetic sound. Interest group Funk-Technik-Freunde, accessed on November 28, 2015 .
- The historical test (02/1973): Tape recorders - audio games for advanced users. Stiftung Warentest, February 4, 2013, accessed on November 28, 2015 .
- ↑ Friedrich Engel, Gerhard Kuper, Frank Bell, Wulf Münzner: Time layers: Magnetic tape technology as a carrier of culture, inventor biographies and inventions. 3rd edition, p. 333 f.
- ^ Hans Knobloch: The tape amateur. Practical guide with the home tape recorder . 1st edition. Franzis-Verlag, Munich 1955.
- ↑ Hermann Bohlen: Say something! Or: Luxuring the bastards - live recordings from the living rooms of the 1960s. Deutschlandradio Kultur, November 11, 2009, accessed on January 21, 2014 .
- ^ A b Ludwig Trainer: The tape industry in Germany and in the world , lecture on the occasion of a press conference of the BASF AG on November 27, 1962.
- ↑ Curt Menke: Tape Primer. The practical guide for tape amateurs . 3. Edition. 1967, p. 12 .
- ↑ Friedrich Engel, Gerhard Kuper, Frank Bell, Wulf Münzner: Time layers: Magnetic tape technology as a carrier of culture, inventor biographies and inventions. 3rd edition, p. 305.
- ↑ Stuzzi Ges mbH, Vienna (1946-1993). Ing.Victor Stuzzi: RKF laboratory (radio, cinema, television). Company history radiomuseum.org, accessed June 21, 2020.