VIDEO CHAIN OF A DOORDARSHAN STUDIO AND OB VAN Qimat Kumar ASSTT. DIRECTOR STI(T)
OBJECTIVES OF DOORDARSHAN STUDIO • 1)
To originate programmes from studios
• 2) To knit various sources of programs i.e., camera output, OB out, M/W, VTR out, video graphics and characters generator etc. • 3) Processing / distribution of different sources. • 4) Routing of programme for recording/ transmission via MSR and Micro Wave.
Activities in a Television studio can be divided into two major areas such as : • 1) • 2)
Action area (Studio) Production control room (P.C.R.)
Action area • This place requires large space and ceiling as compared to any other technical area. • Action in this area includes staging, lighting, performance by artists, and arrangement to pick up picture and sound. • Typical size of TV Studio is 20 x20x8.5 cubic meters
REQUIRMENT OF TV STUDIO • Very efficient air conditioning • Uniform and even flooring for smooth operation of cameras. Acoustic treatment
•
•Effective communication facilities •Studio cameras (three to four) with teleprompter •Tie lines for video and audio from C/R •Cyclorama and curtain
• Luminaires and having grids.
suspension
system
• Audio and video monitoring facilities.
• Studio warning light and safety devices like fire alarm system and fire fighting equipments.
• Digital clock display.
Production control area • Activities in this area are:1.Direction to the production crew by the producer. 2.Timing a production/telecast. 3.Editing of different sources available at the production desk. • Monitoring of output/off air signal
Hardware provided in this area include: 1.Monitoring facilities for all the input and output sources(audio/video). 2.Remote control for video mixer, and special effect (ADO) etc. 3. Communication facilities with technical areas and studio floor. 4. Vision mixing and switching 5. Character Generator (CG)
6. Sync Pulse-Generator (SPG) 7. Camera Control Unit (CCU) 8. Light Control. 9. Audio mixing and control 10. Video Tape-Recorder 11. Electronic Still Storage System 12. Post Production Suites
CAMERA
Electronics &
Patch Panel
M
1
CCU
VDA
2
CCU
VDA
3
CCU
VDA
VCR
VDA
VCR
V I D E O
(Pre View)
P/V MSR
VDA S W I T C H E R
ADO
CG
OBS
FS
SPG 1
OTHER SOURCES
C/O SPG 2
BLOCK DIAGRAM OF VIDEO CHAIN
MW
STAB AMPLIFIER
• Operational requirement from the technical crew may vary from programme to programme. These requirements for lighting, audio pick up and special effects etc. depends upon the programme requirement such as establishing a period, time, formal or informal situation.
Vision mixing and switchingUnlike films, television media allows switching between different sources simultaneously at the video switcher in Production control room operated by the Vision Mixer on the direction of the program producer. The producer directs the cameramen for proper shots on various cameras through intercom and the vision mixer (also called VM engineer) switches shots from the selected camera/cameras with split second accuracy, in close cooperation with the produce. The shots can be switched from one video source to another video source, superimposed, cross faded, faded in or faded out electronically with actual switching being done during the vertical intervals between the picture frames. Electronics special effects are also used now days as a transition between the two sources.
In Video Switcher Mixing is possible • If the sources are having H timing accuracy between 50 ns to 200 ns • Burst phase for SC with an accuracy of 1.5 to 5 deg.
• VISION MIXER (or VIDEO SWITCHER) • Though the video switching is done by the VM at the remote panel, the electronics is located in CAR. The vision mixer is typically a 10 x 6 or 20 x 10 cross bar switcher selecting anyone of the 10 or 20 input sources to 6 or 10 different output lines. The input sources include: Camera 1, camera 2, camera 3, VTR1, VTR2, Telecine 1, Telecine 2, Test signal etc. Some of the sources that have their sync coincident with the station sync are called synchronous, while others having their own independent sync are called non-synchronous.
• The vision mixer provides for the following operational facilities for editing of TV programs:• (i) Take: Selection of any input source or • Cut: switching clearly from one source to another. • (ii) DISSOLVE: Fading out of one source of video and fading in another source of video. • (iii) SUPERPOSITION OF TWO SOURCES: Keyed caption when selected inlay is superimposed on the background picture. • (iv) SPECIAL EFFECTS: A choice of a number of wipe patterns for split screen or wipe effects.
• The selected output can be monitored in the corresponding pre-view monitor. All the picture sources are available on the monitors. The preview monitors can be used for previewing the telecine, VTR; test signals etc. with any desired special effect, prior to its actual switching. •
• The switcher also provides cue facilities to switch camera tally lights as an indication to the cameraman whether his camera is on output of the switcher. • Present day PCR’s have: • • * 24 input video special effects switchers (CD 680 or CD 682-SP) Digital video effects- type ADO 2000/ADO-1000/ADO-100(Ampex) Character generators Telecine/DLS remote controls • Adequate monitoring equipment
• Ampex Digital Optics (ADO-2000) • • ADO is a very useful aid to production. 30 preset effects can be recalled through the keyboard. Various picture manipulations are possible. The picture can be compressed, size can be reduced and cropped into another picture. The principle of operation is that the input Video is converted in digital form using A/D and then the digits are manipulated to create the desired effects and then it is converted back to analog form using D/A. •
• Ampex Digital Optics (ADO-2000) • • ADO is a very useful aid to production. 30 preset effects can be recalled through the keyboard. Various picture manipulations are possible. The picture can be compressed, size can be reduced and cropped into another picture. The principle of operation is that the input Video is converted in digital form using A/D and then the digits are manipulated to create the desired effects and then it is converted back to analog form using D/A. •
• CHARACTER GENERATOR • Characters Generators are provide titles and credit captions during production in Roman script. It provides high resolution characters different colors for colonizing characters, background, edges etc. At present bilingual and trilingual C.G are also being used by Doordarshan. •
• Character Generator is a microcomputer with Texts along instructions when typed in at the keyboard is stored on a floppy or a Hard disk. Many pages of scripts can be stored on the disk and recalled when needed, by typing the adresses for the stored pages, to appear as one of the video sources. •
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Central apparatus room This is the nerve center for a television station. Activities in this area include: 1 Distribution of stabilized power supply to different technical areas with protection devices. 2. Sync pulse generation and distribution. 3 Distribution of sources to various destinations 4. Video processing and routing. Electronics for camera chain, video switchers, special effect generator, and test signal and pattern generator. 6. Monitoring facilities 7. Patch panel for video and audio lines 8. Electronics for micro wave links
Sync Pulse-Generator • It is essential that all the video sources as input to the switcher are in synchronism i.e., start and end of each line or all the frames of video sources is concurrent. • SPG is normally duplicated for change over in case of failure.
SPG provide the following outputs: • -Line drive • -Field drive • -Mixed blanking • -Mixed sync • -colour subcarrier • -A burst insertion pulse -PAL phase I-dent pulses
GENLOCK (slaving) • In production it is necessary to mix between two sources which are not synchronized. • This is possible when the local SPG has been synchronized with the external source. • To overcome this problem, SPG is fitted with a GENLOCK facility. • More than one sources can be synchronized by digital Frame synchronizer.
• 1. Camera control unit (CCU) •
2. Light control unit(LCU) and a dimmer room
• 3.
Audio control room (ACR)
• 4.
Video tape recording room(VTR)
• 5.
Telecine(T/K) and film section
• 6.
Digital library store(DLS)
• 7.
Video graphic or paint box(PB)
Post production and editing suites for outdoor works by the ENG? EFP section (Electronics News gathering/Electronic field production).
• 8.
• Camera control unit • The television cameras which include camera head with its optical focusing lens, pan and tilt head, video signal pre-amplifier view finder and other associated electronic circuitry are mounted on cameras trolleys and operate inside the studios. The output of cameras is preamplifier in the head and then connected to the camera control unit (CCU) through long multicore cable (35 to 40 crores). •
• All the camera control voltages are fed from the CCU to the camera head over the multicore camera cable. The view-finder signal is also sent over the camera cable to the camera head view-finder for helping the cameraman in proper focusing, adjusting and composing the shots. • • The video signal so obtained is amplified, H.F. corrected, equalized for cable delays, D.C. clamped, horizontal, and vertical blanking pulses are added to it. The peak white level is also clipped to avoid overloading of the following stages and avoiding overmodulation in the transmitter. The composite sync signals are then added and these video signals are fed to a distribution amplifier, which normally gives multiple outputs for monitoring etc.
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Light Control The scene to be televised must be well illuminated to produce a clear and noise free picture. The lighting should also give the depth, the correct contrast and artistic display of various shades without multiple shadows. The lighting arrangements in a TV studio have to be very elaborate. A large number of lights are used to meet the needs of ‘key’, ‘fill’, and ‘back’ lights etc. Lights are classified as spot and soft lights. These are suspended from motorized hoists and telescopes. The up and down movement is remote controlled. The switching on and off the lights at the required time and their dimming is controlled from the light control panel inside a lighting control room using SCR dimmer controls. These remotely control various lights inside the studios
– Modern TV studios have a computer-controlled lighting system the intensities of various lights can be adjusted independently and memorized for reproduction. The status indication of lights regarding their location and intensity is available on a monitor/MIMIC display. During reproduction of a particular sequence, the information from the memory operates the respective light dimmers. Hand held control boxes are also available for controlling light intensities inside the studios which communicate via a control panel. Most of the operational controls of the computerized light control system can also be performed manually with the back –up matrix and fadder controls.
• Sound mixing and control • As a rule, it television, sound accompanies the picture. Several microphones are generally required for production of complex television programs besides other audio sources also called marred sound from telecine, VTR, and audio tape/disc replays. All these audio sources are connected to the sound control console. • The sounds from different sources are controlled and mixed in accordance with the requirement of the program. Split second accuracy is required for providing the correct audio source in synchronization with the picture thus requiring lot of skill from the engineer. Even the level of sound sometimes is varied in accordance with the shot composition called prospective. •
• Audio facilities • An audio mixing console, with a number of inputs, say about 32 inputs is provided in major studio. This includes special facilities such as equalization, PFL, phase reversal, echo send/receive and Digital reverberation units at some places Meltron console tape recorders and EMI 938 disc reproducers provide for playing back/creating audio effects as independent sources (Unmarried) to the switcher. •
• Video Tape recorders • VTR room is provided at each studio center. It houses at least two console type 1 ” videotape recorders (VTRs) and a few Broadcast standard Videocassette recorders (VCRs). In these recorders, sound and video signals are recorded simultaneously on the same tape. •
• ACCESS TO ELECTRONIC STILL STORAGE SYSTEM • Some PCRs have access to the electronic still storage system. One replay remote control of the digital library system is mounted on the video production control table at the PCR. Still pictures stored in the library system can be recalled and used in production by selecting them by their addresses either from the local or from the remote control pannel after recomposing if desired. •
Post production suites • Most of the present day shootings are done on locations using single camera. The actual production is done in these suites. The job for a post production suites is:• a. To knit program available on various sources. • b. While doing editing with multiple sources, it should be possible to have any kind of transition. • c. Adding/Mixing sound tracks. Voice over facilities. • d. • e. Creating special effects. •
Coverage of Outside events • Outside broadcasts(or OBs) provide an important part of the television programs. •
Major events like sports and important functions are covered with an O.B. van which contains all the essential production facilities.
Video chain • Output from the switcher goes to stabilizing amplifier via PP and VDAs. Output from the stab. Is further distributed to various destinations. It may be noted that the use of VDAs helps to monitor the video signal at different locations and the use of PP is very helpful for emergency arrangements during breakdowns and trouble shooting. A separate monitoring bus is provided in CCU, LCU and END CONTROL with sources as shown. END CONTROL also has a remote for the adjustment of levels etc. in the STAB AMP unit. Route for the other sources is similar to this and can be understood from the block schematic.
