D-3 - the format of digital composite video was developed by NHK jointly with Panasonic and the latter is hardware implemented. With this format in 1991, Panasonic entered the market for the first time, putting them on the Air Force . Professionals were impressed by the choice of a tape half an inch wide (12.7 mm). This allowed, finally, to create a compact, with a small mass of VCRs. Moreover, the increased recording density (which is 13.7 Mbit per square centimeter) has reduced the consumption of the tape, and hence reduced operating costs. By December 1991, around 1000 video recorders of this format were delivered to different countries of the world.
D-3 | |
---|---|
D-3 format video tape | |
Media type | Magnetic tape Video cassette |
Content format | PAL NTSC |
Counting mechanism | Tilt footage |
Recording mechanism | Tilt footage |
Designed by | NHK |
Application | Video production |
Year of issue | 1991 |
By creating the first digital camera head AQ-20, Panasonic was able to realize for the first time a digital camcorder. Adding to this and the entire further line of television production equipment, the company introduced to the world a complete digital production system covering studios, outside production and videojournalism, editing and issuing programs on the air - in short, all known TV production processes.
Content
Format
Composite format D-3 television signal sampling rate is four times the color subcarrier frequency (4 Fsc, for PAL signals it is 17.73 MHz), the number of quantizing bits is 8 bits each. 48 KHz audio sample rate when quantizing 20 bits per sample. There are 4 audio channels, applied azimuth recording.
The time code track directly adjoins the book edge, its width is 0.45 mm. The gap between the tracks of the time code and the control channel is 0.45 mm, and the width of the latter is 0.4 mm. The inclined line width is 18 microns. The total length of the software line is 117.71 mm, and the video sector is 108.9 on it. The angle of the lines here is the smallest - 4.9 degrees.
To protect against errors, Reed-Solomon codes are used, internal and external. Both contain 8 verification characters. The internal code corrects random errors that occur in the recording-playback channel. It allows you to correct up to 4 erroneous bytes from 86. The external code allows you to correct packet errors, the main cause of which is the loss. The potential of the error protection system is significant, since the matrix of the code block corresponds to the TV field. However, they are enhanced by mixing before writing data (also on the field interval), which significantly expands the masking of detected but not corrected packet errors, since they are scattered across the field and reproduced as single flashes or dips. All this reduces the subjective visibility of errors, and, therefore, improves the quality of the perceived image.
The channel code is a modified 8/14 code, which successfully combines the advantages of the BVN codes with scrambling and the Miller code in the square. By this code, 8-bit words are converted to 14-bit words. Of the total number of 4096 variants, then 256 words are selected that are most fully adapted to the channel.
New laminated amorphous magnetic heads have been developed for D-3 video recorders. Their increased EMF and broadbandness are well combined with high-coercive (high-energy) metal-powder magnetic tapes. Together with the principle of azimuth recording, it was possible to achieve an extremely high surface recording density of 200 Kbps per square mm. The working head gaps are turned by +20 and −20 degrees.
The sound data falling on the field interval is combined into sectors recorded at intervals for editing - only 4 sectors per field, in each sector two halves with different azimuthal direction of the strokes. Here, the error correction system uses the entire area of the tape and all recorded data.
The development of D-3 video recording equipment was accompanied by a series of innovations. One of them is a precision tape drive mechanism, in which the belt tension is significantly reduced. As a result, the service life of video heads has doubled in comparison with D-1 tape recorders (Sony) . For the first time, rotating erase heads with a working gap, the length of which is twice the width of the recording line, are applied. Pass-through mode allows you to control the quality of the recording. Recording mode with pre-play (Preread mode) is possible, when the universal head plays and the player plays. This mode greatly expands the installation capabilities of video telegrams - the same device can be used both as a source and as a master.
Three types of cassettes are used in the D-3 format: small (65 min), medium (125 min), and large (245 min).
Specifications
Video
- The sampling rate, MHz - 17.73 (PAL) and 14.32 (NTSC)
- Coding Standard - 4fsc
- Recordable Video - Composite
- Quantization, bit / count - 8
- The flow of information (full), Mbps - 154
Sound
- Sample rate, kHz - 48
- Quantization, bit / count - 20
- The number of channels - 4
Format options
- Number of video heads - 10
- Rotation speed, rev / s - 100
- Angle of the video line - 4,9173 °
- Width of lines, micron - 18
- Step lines, microns - 18
- Azimuth - +/- 20 °
Media options
- Tape width, mm - 12.65
- The thickness of the tape, microns - 11-14
- Working layer - Metal powder
- Recording time on tape, min .: 65, 125, 245
See also
- Video