Magnetic recording
A magnetic recording ( MAZ ) is an electronic analog or digital recording of content of a visual, acoustic or abstract nature on magnetic media , mostly magnetic tapes ( magnetic tape recording ). In professional parlance, MAZ stands for the video tape formats and devices used in television companies . The term is rarely used for home video formats and audio recording ( tape ).
Similar to the " floppy ", the name originally intended for the information carrier has been misused in everyday language for the recording device. In television broadcasters and television production companies, decks are typically video players or recorders used for editing or broadcasting .
VTRs in colloquial use are primarily characterized by the fact that they are capable of timecode , can be controlled image-accurate by an editing control, can perform image-accurate cuts and use professional standards for signal transmission (symmetrical audio cabling via XLR , transmission of the image in FBAS ( Composite, color image blanking synchronous signal ), component video ( YPbPr ) or serial digital interface ( SDI ) via coaxial cable ). With SDI, the image and sound signals are transmitted digitally over a single cable.
Typical decks of the beginning of the 21st century fit in 19- inch cabinets ( racks ), can be carried by one or two people and record the data on magnetic tape cassettes. Since 2004, VTR devices that use hard drives have also been offered. Optical media and memory cards are also offered as alternative storage media to tape.
Typical MAZs prior to the cassette era recorded magnetic tape wound on large open reels , each taking up at least as much space as a 19-inch cabinet. They were rollable to make transport easier.
VTR formats in use today are Betacam SP , Digital Betacam , HDCAM , IMX , DVCAM , DV , D-9 , DVCpro and DVCproHD .
Among television journalists, the term MAZ is also used as a synonym for a film report (classically with original sounds ). These film reports are usually around two and a half to five minutes long. In contrast to this, there is the NIF ( message in the film ), a message underlaid with moving images that is kept for no longer than 60 seconds.
Working principle of magnetic recording
A write head is required to store information on magnetic tape. The write head consists of a highly permeable core and a coil with six or seven turns. A magnetic field is generated by an inoculation current flowing through the coil, which must exit through a small air gap on one side of the magnet. The air has a much greater magnetic resistance than the material of the write head. Now the magnetic field lines penetrate the magnetic tape to be written on. Due to the special tape coating, the tape can be magnetized by the magnetic field. The information is stored on the tape in the form of small permanent magnets - small magnetic fields. The lower the frequency of the recording current, the greater the length of a permanent magnet. The actual information that will be used later for reading is stored in its length.
Technical development
Until 1970
Attempts to store images on shellac records ( Baird Phonovision , 1928) and magnetic tapes began in the 1920s to 1940s . However, the results were unsatisfactory. It was not until 1956 that Ampex presented the VR 1000, the first machine that recorded a BAS signal (black and white video signal) on 2- inch magnetic tape. The weight of the machine was 400 kilograms and the tape reels weighed 15 kg. Another disadvantage was the design based on the electron tube, so picture fluctuations were inevitable. The image tracks were written transversely to the direction of the tape using the segmented Direct FM method, which corresponds to 5 tracks per field at 60 Hz NTSC transmission. This machine was nicknamed 2-inch quadruplex , which was usually abbreviated to 2-inch quad . For the first time it was possible to record sound (mono) and image on a tape, whereby the cut was initially carried out mechanically. Since the picture and sound heads were not placed in the same place, a decision had to be made as to whether the sound or the picture should run synchronously. The format was only used in the studio to save film material and expensive development and scanning times in film recording . From 1958 the 2-inch quadruplex could also record in color in the NTSC system and in the same year black and white recording on 2-inch quad was introduced on German television. As a further development, the 2-inch high-band (hi-band) with stereo recording was available from 1964 . In the same year Sony launched the 1-inch EV format, whereby the recorder was heavy but portable. The format could initially record an hour in black and white on an inch wide tape. Later models of the EV-200 and EV-300 series could record in color using an external adapter. The system was only used for school and industrial purposes.
The successor format CV format from Sony with 1 ⁄ 2- inch tape appeared in the same year and also served industrial purposes. The machine was a "skip field" recorder, so only every second image was recorded, but this was scanned twice during playback. In 1966 an American 2-inch black-and-white MAZ RCA TR 22 was modified for the first PAL recordings in the WDR color laboratory in Cologne, and the experience gained was incorporated into the color-compatible successor TR 70 from 1967 onwards. A year later, Philips developed the LDL video format, the first video format intended for home use. 45 minutes of video and audio could be recorded on the open reels.
In 1969 Akai started a series of portable devices and 1 ⁄ 4- inch tape with a recording time of 20 minutes per reel. The tape used the omega wrap around the head drum .
1970 to 1979
In 1970, the Electronic Industries Association of Japan (EIAJ) introduced a 1 ⁄ 2- inch video system in which Sony was involved. It was the first time that several manufacturers, in this case mainly Sony and Panasonic, merged and developed a format. There were disputes between the individual members about the color specifications and the pilot tone system. Reel and cassette devices existed for the system and it also found its way into the end customer area , so that mainly family videos and industrial films were found on the reels or cassettes. The original EIAJ specification could only record black and white images; only the further development EIAJ-2 could record color images.
In 1971 Sony launched U-matic , a color-under system with a 3 ⁄ 4 inch tape and one hour playing time. The video bandwidth was max. 3.4 MHz and thus about half of the 2-inch systems. The FBAS signal, two audio channels and a CTL track were recorded. Although not originally intended to be a professional video system, it has been increasingly used on the daily news by US television networks. The cassettes were more compact than previous formats and were better suited for use in portable devices.
Philips introduced the VCR format for home use in 1972 , in which the reels were stacked in the compact cassette. The maximum playing time was about 70 minutes. The format had two audio channels and worked according to the color-under method.
The development of the 2-inch quad entered the final stage in 1974 - the 2-inch super-high tape, in which time-code-controlled copying could be used to cut to another tape. A year later, Sony launched the 1 ⁄ 2- inch home system Betamax in the USA , in which a composite signal and a sound track could be recorded using the color-under method. The playing time was a maximum of 180 minutes, the bandwidth about 3.2 MHz, which corresponds to a resolution of 250 lines. In the same year, BTS / Bosch released the 1-inch B system, which became the analog standard for ARD and ZDF. A composite signal was recorded using the Direct FM method with a bandwidth of 5.5 MHz and segmented, with a field being distributed over 6 tracks. In this format, the video tape is wrapped around a small head drum in alpha wrapping. Due to the mechanical inaccuracies of the tape run, a Time Base Corrector is required in the playback path for playback and wherever Direct FM formats are played back. A digital field memory was used for the use of slow and fast motion. Three analog longitudinal audio tracks can be recorded, whereby track 3 was mostly used for the longitudinal time code , but a vertical interval time code could also be recorded. The playing time was a maximum of one hour. A portable device (BCN 20/21) was also developed in which the two reels were on top of each other and the playing time was 20 minutes.
1976 was the Video Home System with 1 / 2 -inch JVC presented. This records a composite signal (chroma according to the color-under system) and a sound track. The playing time is up to 4 hours (later also up to 5 hours, which then resulted in 10 hours in long play). In the same year, the production of 2-inch quad machines is stopped; Recording media were still available for some time afterwards.
Sony launched U-matic Highband (Hi-Band) in Europe in 1977. The previous U-matic format thus became the Lowband (Lo-Band), which was the only U-matic system in the USA. The color bandwidth in particular was increased from 600 kHz (Lo-Band) to 1 MHz, which means that more colors can be displayed. The resolution increased from 250 to 260 lines. With the system, the first ENG missions became possible, e.g. B. during the Rhine flood from a rowing boat in Cologne's old town.
Sony and Ampex introduced 1 inch C in 1978 , which established itself as an international standard. The specifications are similar to the one-inch B format, but the signal recording was not segmented, so that one field corresponds to one track and four analog longitudinal audio channels are available. One of them (channel 4) was used per se by the deck as a sync channel, the third as an LTC channel. The head drum was wrapped in an omega shape. A year later, Philips and Grundig introduced Video 2000 , a 1 ⁄ 2- inch tape system. However, it only uses 1 ⁄ 4 inch, since the cassettes are reversible like compact cassettes , and offers eight hours of recording time in SP mode.
1980 to 1989
For home users, portable recorders and camcorders for the VHS-C format were introduced in 1980. These scaled down VHS cassettes offer a maximum playing time of 30 minutes. With a mechanical adapter, VHS-C cassettes can also be used in conventional VHS devices.
In 1982 Sony introduced Betacam and JVC M (also called Chromatrack-M). Both systems record analog component signals ( YUV ). The first 8 mm camcorders for Video 8 appeared in 1984 and worked according to the color-under method. A FBAS signal in VHS quality and two audio channels as AFM sound / HiFi sound were recorded.
In 1985, super beta hi-fi devices appeared with an image resolution of 285 lines and recorded AFM sound. In the same year, device production for one-inch B and C formats is discontinued. The tapes were available until the 1990s and in use as recording media until then. BTS tries to go the way to HDTV with a one-inch tape format: The development has 1250 picture lines with 50 fields with analog component signals (HD-MAC transmission format), 4 tracks per segment, 8 segments per field and analog sound recording. However, the BCH 1000 machine was only manufactured in small numbers.
Sony introduced the improved Betacam SP in 1986 . There is now a large type of cassette up to 100 minutes, with which almost all programs could be recorded with one cassette. As standard, the format has LTC and VITC time codes, 2 longitudinal sound tracks, 2 AFM sound tracks as well as a luminance track with 5.5 MHz and a chrominance track with 2 MHz bandwidth, so that the resolution of the one-inch systems was achieved for the first time with a cassette format , since the video bandwidth mainly determines the image sharpness or resolution. Complex studio environments were required for this format, and all subsequent professional standards built on the experience and specifications of Betacam SP. The running times of the larger cassettes are 30, 60 or 90 minutes, the smaller ones 5, 10, 20 or 30 minutes. A recording device, the Sony BVW 85, is able to record 2 audio channels as PCM audio, provided the longitudinal audio track is used 1 is used. Panasonic published MII as Betacam competitor with a running time of up to 97 minutes.
The U-matic SP standard was also introduced in 1986. The resolution was further increased with 330 lines at 4.2 MHz. The time code is now as Hi band with an additional generator recordable. Another new feature is Dolby C noise reduction for the audio tracks. Portable devices are now also available for U-matic SP. With D-1 the first digital cassette format appeared with 3 / 4 -inch tape in which the scanning of the component signals in the ratio 4: 2: 2 at 13.5 MHz and 6.75 MHz chrominance luminance was carried out. The quantization was done with 8 bits. Four mono or two stereo audio signals with max. 20 bit to 48 kHz can be recorded. An audio track can be recorded longitudinally for orientation in shuttle operation. There were 3 cassette sizes with 12 minutes (S), 34 minutes (M) and 94 minutes (L).
In 1987 the S-VHS standard was introduced: With special tapes, up to 400 lines of resolution at 4 MHz can theoretically be achieved. In contrast to U-matic, the tracks are written overlapping, they are shorter and the tape speed is very low. With this format, the S-Video connection was introduced, which transmits luminance and chrominance (brightness and color) separately. A composite signal, two longitudinal audio tracks, two AFM sound tracks and the VITC time code are recorded. If the longitudinal audio track 2 is used, the LTC can be recorded. S-VHS prevails primarily in the semi-professional area.
D2 (D-2) was introduced by Ampex / Sony in 1988 and, like D-1, worked with a 3 ⁄ 4- inch tape, but with FBAS instead of component inputs and outputs. The image is quantized with 8 bits, the sound recording is identical to D-1. The video bandwidth is 6.5 MHz. In the same year, Philips stopped manufacturing Video 2000. ED-Beta also appeared , but it did not catch on. With 520 lines it had a much higher resolution than S-VHS, but was not published in Europe. As with Super-Beta, ED-Beta required special recording media, since otherwise only normal beta mode was possible. In 1988 Hi8 was also introduced as the successor to Video8. The resolution is higher than with S-VHS and the recording of longitudinal audio tracks is completely dispensed with. The audio track is recorded in the form of AFM sound and / or PCM sound with up to 15 kHz and an 8 mm time code can be recorded.
In 1989, a year after D2, D3 (D-3) was introduced. The specifications correspond to the D2 format, but the tape is now only 1 ⁄ 2 inches wide, the play lengths are 50/64 minutes (S), 95/125 minutes (L) or 180/245 minutes, depending on the tape thickness. (XL). That same year Sony launched HDVS , a one-inch reel-based system for digitally recording HDTV signals. Eight mono or four stereo audio signals can be recorded, plus two analog cue tracks and one analog LTC track. The system was only used in Japan, it worked with YUV.
1990 to 1999
In 1993 Sony introduced Digital Betacam . YUV components are recorded that are digitized with 10 bits at a ratio of 4: 2: 2 (in contrast to 8 bits for other formats), which results in a data reduction of 1: 2. The sound (4 audio channels) is digitized with 20 bits at 48 kHz. Digital Betacam is still the widely accepted broadcast standard. The SDI connection was new . Component video, audio and time code are transmitted digitally at 270 Mbit / s in a self-clocking manner via a BNC cable. The playing time is similar to that of Beta SP. That same year, Ampex introduced DCT in the United States , a 3 ⁄ 4- inch system with component recording, 8-bit quantization, and 4 channels of audio quantized with 20-bit at 48 kHz. The operating mode can be switched between NTSC and PAL. The production of Betamax has been discontinued.
In 1994 Panasonic introduced the D5 format (D-5). The 1 ⁄ 2- inch tape remained, only digital component recording was used now. It could be quantized with either 10 or 8 bits. D-3 tapes could be played, otherwise the specifications were the same as for Digibeta or DCT. UNIHI from Sony appeared on the Japanese and American markets . It was the first cassette system for HDTV and replaced HDVS. The video bandwidth is 20 MHz, YUV recording and 4 audio channels.
A year later, BTS introduced D6 (D-6), an HDTV system with 30 MHz video bandwidth, component recording and 12 digital audio channels. W-VHS (Wide VHS) was presented in Japan: analog HDTV with a video bandwidth of 13 MHz, chrominance bandwidth 4 MHz. YUV for video, AFM sound for audio and digital audio (PCM sound) are recorded on 2 tracks each. The manufacture of the U-matic system has been discontinued.
The digital video (DV) format was introduced on a broad basis at the beginning of 1996. It should be an inexpensive consumer format. The data rate is 25 Mbit / s, which corresponds to a compression of 5: 1 and a video bandwidth of around 5 MHz, 2 sound tracks are recorded with 12 bit or 16 bit with 44.1 or with some devices 48 kHz PCM sound. Locked audio is optional. The FAST Video Machine was a pioneer in this area. There were several cards (16 bit ISA) and three or four boxes to be placed outside the computer (input and output, signal processing). The Media 100 system for the Mac also led the way at the time, Windows 95 still lacked important support. In the same year Sony introduced DVCAM , which differs from DV only in that it has a 50% higher tape speed (resulting from the larger track width) and locked audio. Four audio channels are technically possible, but then only 32 kHz and 12 bit. A 60 min. DV tape is equivalent to 40 min. DVCAM. Sony also released Betacam SX for use in daily news and coverage. The system records in the MPEG-2 standard, scans 4: 2: 2 and compresses with DCT intraframe 10: 1. The runtimes are similar to those of Digibeta. The counterpart from the warehouse of the competition JVC was the System Digital S (also called D-9) in 1996 . There were no other devices here except the decks. The compression according to DCT is 3.3: 1, which corresponds to 50 Mbit / s. The development was based on the experience of the S-VHS and the W-VHS systems . The dimensions of the cassettes correspond to the VHS.
In 1997 Sony developed the HDCAM format , which was the HD successor to Digital Betacam. HDCAM cameras record 1920 × 1080 pixels at 24, 25, 30 and 100 frames per second. The tape formats subsample 1920 × 1080 pixels at YCbCr 3: 1: 1 with 8 bit quantization. The format was used for the production of feature films such as Star Wars or Collateral . With over 30,000 systems sold by 2007, HDCAM was by far the market-leading professional format for digital cinema production and HDTV.
In 1999, Panasonic introduced the DVCPro 50 system, which, like Sony's DVCAM, processes 50 Mbit / s. It scans 4: 2: 2 and compresses to 3.3: 1 according to DCT. Most decks can read DV, MiniDV, DVCAM, DVCPro (25) and DVCPro50 because the DV formats use identical cassettes. IMX MPEG was introduced by Sony in the same year. It is a format based on MPEG technology. The video data can be addressed directly as files when editing and copied accordingly to the computer. DCT compression compresses 3.3: 1. It was z. B. used by RBB in addition to BetaSX for news. Decks like the MSW-A2000P from Sony play Betacam, Betacam SP, Digital Betacam, Betacam SX and IMX. They were used in broadcasters that used several formats in parallel, especially in the still often used 3-machine editing suites as feeders. The Digital8 , also launched in 1999 , records the same quality as MiniDV or Normal DV, only on 8 mm tape. A 120-size Hi8 cassette records 60 minutes of Digital8 video. In the meantime these devices have disappeared from the market due to the drop in prices for DV and the smaller cassettes and thus also smaller camcorders. Most devices also play Hi8 and Video8.
2000 until today
JVC introduced the Digital Video Home System (D-VHS) in 2001 . It records at twice the DVD data rate on VHS cassettes, which corresponds to around 16-20 Mbit / s and is the first consumer recording device for HDTV signals.
In 2003 Sony introduced the further development of HDCAM : HDCAM SR . In addition to YCbCr, it also offers RGB in 4: 4: 4 sampling with 10 bit quantization. A year later, the production of the Betacam SP system was finally stopped; Recording media were still available, however, this forced the switch to Digibeta, BetaSX, IMX or even to HD. In 2004, the High Definition Video format was introduced, which is intended as a semi-professional format. In contrast to DV, it uses MPEG2-GOP data reduction in which groups of images are used for data reduction. The format works on the basis of the 1080i format; however, almost all devices allow conversion to SD formats. Meanwhile, HDV cameras are also used in the broadcast area and the camera manufacturers sell cameras tailored to professional users.
Further format extensions appeared on the market in 2005: Panasonic's D5 (D-5) and DVCPro 50 formats were further developed into D5 HD and DVCPro 100 . From 2006 onwards, manufacturers increasingly offered cameras and editing systems in which magnetic recording was dispensed with and instead tapeless recording on the Professional Disc for Broadcast (Sony XDCAM ) derived from the Blu-ray Disc or on memory cards (Sony SxS , Panasonic P2 or Ikegami Editcam ) takes place.
See also
literature
- Jürgen Burghardt: Manual of the professional video recorder . Edition Filmwerkstatt, Essen 1994
- Johannes Webers: Handbook of film and video technology . Franzis Verlag, Poing 2000 (6th edition)
Web links
- Quadruplex Park Museum of Broadcast Technology (English)
- Historical television laboratory of the Bergische Universität Wuppertal