T356 Fall 2012 - Week 7
- Graphics/Studio gear and signal flow quiz next week
- Cover switchers and other studio equipment
- News exercise in lab this week
- Produce Demonstration Videos next week and the week after. Look at the Demonstration Video Schedule
- Then the performance piece and then the PSAs.
PSA Reality Check - We will
schedule PSAs in just a few weeks. Please
check with your client to see if they are still willing to have a PSA prodcued and if they have a specific time preference.
(Every pair will get a 25-minute block of time) If you don't have a preference,
I'll simply block it out to try to group all of the projects with
similar production treatments.
Demonstration videos. I've created groups and posted a schedule. We start producing these next week. We'll take lecture time today for you to meet with your group member. Be sure to delegate responsibilties: audio design, graphics, set & lighting design, etc. We're shooting these starting next week.
Cybercollege Readings - 57 (timecode) & 60 (studio)
Signal Flow in the Studio
In a TV production studio you often hear the words "upstream" and "downstream." These
terms use the analogy of water flow to represent the flow of the video
signal to various pieces of equipment in the studio. Think of a camera
as being the most upstream element in the studio. This is where the signal
originates. After the signal comes out of the camera CCU, it flows downstream
into the input of the switcher. Once inside the Grass Valley switcher
in Studio 5, the signal flows from the Preview and Program busses to
the keyer. So the keyer is downstream of the program bus. After the keyer,
the video flows to the Master/Panic Black switch. So whatever we do on
the Program or keyer stage can be covered by the Master/Panic Black button.
After leaving the switcher, the video flows downstream to a VTR.
There are several important pieces of studio equipment that
you should be familiar with: TBCs (time base correctors), waveform monitors,
vectorscopes and switchers.
TBC (time base corrector)
A TBC, is a piece of equipment used to correct instabilities in analog
video signals, provide synchronization between video signals, and adjust
phase differences in signals to correct color or make them consistent
with other signals. TBCs usually have a "proc amp" which lets
you "tweak" or adjust the video's brightness, hue, saturation
If you have a copy-protected VHS tape or DVD that you need to dub, you
can run the video through a TBC. It strips the old sync, which has been
modified to create dubbing problems, and replaced it with new sync.
A device used to examine the luminance portion of the video signal and
its synchronizing pulses.
- Analog (NTSC) black should register at 7.5 IRE on a waveform monitor
- ATSC/Digital black levels should be 0 IRE
- White level (both NTSC and digital) shouldn’t be any greater
than 100 IRE on a waveform monitor
- 20 IRE units equals one f-stop
A vector display measuring device that allows visual checking of the
phase and amplitude of the color components of a video signal. NOTE:
You can't adjust or manipulate a video signal just by using a waveform
monitors and vectorscopes. They simply let you examine the signal. You
must use a TBC, a camera control
Provides synchronizing pulses that are fed to the TBCs
and cameras to keep them all running. All the horizontal/vertical
retracing and scanning must happen at the same time in order to blend
the video signals together with a switcher.
Video switchers allow the user to select and mix video signals. They
also provide a limited degree of effects.
- Select appropriate source from several inputs
- Perform basic transitions
- Create/access special effects
Switchers can have a number of different busses. A buss is simply a
row of buttons, which allow the operator to select which input goes out
to a particular destination. Usually there are at least three different
busses on a production switcher:
- Program bus: whatever source is selected goes to
the program monitor
- Preview bus: identical in appearance to the program
- Effects bus: used to select sources for different
- Cut or take (Ready 1- take 1)
- Flip flop of program/preview bus
- Dissolve: (standby 1- dissolve to 1)
- Super (superimposition: using the fade bar and keeping it halfway
- Fade: (a dissolve with black)
Special Effects & controls:
- Wipes & wipe patterns (see below)
- Key & clip controls (chroma key, luminance key)
- Downstream keyer
- Color background controls
Wipe: when one image replaces or uncovers another (Write
deko does this)
Soft wipe: you can set the border to be soft (fuzzy) by a knob on the switcher
Wipe pattern: the geometric shapes you can choose from
(diamond, circle,) these are standardized and referred to by numbers
so that EDLs (edit decision lists) can pull them up consistently from
Wipe positions and directions: al wipes can be reversed
(by pressing the reverse button on the switcher) or stopped partway by
stopping the fader bar.
Split screen: if you stop a horizontal, vertical or
diagonal wipe halfway you get a split screen.
DVE (digital video effect) allows you to actually squeeze,
rotate, flip, shrink or expand the image. Grass Valley uses the abbreviation DPM (Digital Picture Manipulation) instead of DVE- but they both mean the same. DVEs or DPMs allow for shaping or distoriting the video in interesting ways, including perspective,
squuezes, page turns, flips etc.
Keys: When using keys, the switcher replaces part of
the video signal with video from another source. There are several types
of keys you can do with a production switcher: luminance
chroma keys and external keys.
- Luminance keys work on brightness. If someone is standing in front
of a black background, you can use a luminance key, adjust the threshold,
and key out the dark
areas. Similarly you can key out the brightest areas of an image. The
problem with this type of key is that it's not very precise to remove
video based on luminance. If we key out the dark areas, everything
else that's equally dark will be removed as well (shoes, pupils in
eyes, buttons, etc)
- Chroma keys work by selecting and removing specific
colors. This is usually how the weatherman standing in front of a map
is produced, or "on-location" shots of news people who areen't really
on-location. The two most popular colors to use are blue and green.
This is because these
people's hair and skin. Studios and production companies usually have
both a green and a blue screen. If the talent shows up wearing blue,
you use the green screen and vice-versa.
- External or Linear keys are fed by an external source, such
as a character generator. The external device sends two video signals:
the key and video fill. The key signal acts like a cookie cutter telling
the switcher what video to remove. The video fill is what goes into
the cut out portion.
You should also be aware of the term downstream key, which is a key
that happens downstream or after the video leaves the switcher. It's possible
to get a downstream keyer that inserts the station ID or weather warnings,
Switcher types & functions
The Grass Valley switcher in Studio 5 is just one type of switcher.
There are several different types of switchers designed for different
- Production switchers are used for live production. (like
the Kayak Grass Valley we have in Studio 5)
- Post-production switchers (used for primarily for
editing) Most of the switcher's functions (such as wipes, dissolves, etc.) can be remotely controlled by the Editing
Control Unit. These are now rare as most editing is being carried out with non-linear systems (Avid, Final Cut Pro, etc.).
- Master control switcher: These are optimized for switching and controlling numerous video sources and playback devices (VCRs digital cart machines, etc.). These generally won't have a lot of effects but focus on video previewing and insertion of station IDs and weather warnings.
- Routing switchers: Similar in function to a patch
bay. Some routing switchers are nothing more than a row of buttons.
Some are computer-based and can be programmed with a variety of setups.
Master Control Switcher
Simple Routing Switcher
Don't forget Audio
Audio follow video switchers. Audio switching is sometimes done by a separate device (other than the video switcher) The term "audio follows video" refers to devices that control
or trigger an audio switcher. The result is that when you swicth a video source, the audio follows along.
In the recent past, broadcasters across the nation replaced their old analog gear with digital. Stations that might have used analog RGB routers, distribution amps, and switchers had to toss/sell/scrap/retire the gear and build an entirely new system based on an HD-SDI infrastructure.
Video Recording Systems
Tape - Videotape can be in the form of open reel or more commonly found cassette shells. (miniDV, DVCPro, HDCAM, etc.)
Magnetic Disk - Uses one or more magnetic disk drives (commonly referred to as a "hard drive"). Mutlple drives are often cofigured as a RAID (redundant array of independent disks).
Optical Disk - Many camcorders write video directly to optical disks. Sony's XD Cam is one example (E.g. BluRay).
RAM-based (uses solid state memory) Now found on many consumer and professional camcorders. (Panasonic P2 cards, Compact Flash, Memory Stick, etc.)
Cables and Connectors
How does one get video from one device to another? Typically through
a cable and a connector. For analog video, the choices include:
- Composite (single cable) This is the "lowest
common denominator." Every video recording & playback unit
has this. Try to avoid as the composite video signal is prone to a
variety of artifacts. Connectors: RCA (consumer) & BNC (porfessional)
- Y/C (a.k.a. S-Video) The idea is to keep the signal
broken down into the luminance & chrominance components. This is
much better quality than composite. You can find Y/C ports on everything
from consumer camcorders to high-end digital VTRs. Connectors:
single, multi-pin connector on each end.
- Color difference / Component The signal is split into three
components: Y, R-Y, B-Y.; YUV; or Y'Pb'Pr'. The Y is for luminance,
the U is for the blue color difference, the V is for the red color
difference. Most high-end VTRs (Beta, MII, DV and digi beta, etc) have
these connectors on them. This is the norm for getting Beta SP footage
into an editor. It's a tad better than the Y/C system. Connectors:
Usually three BNC connectors on each end. RCA connectors are often
used on consumer DVD players and projectors.
- RGB (true component) The Red, Green & Blue signals
are kept separate. Not as common as the color difference system. While found on higher end broadcast interfaces, true component takes a great deal of bandwidth. Connectors:
BNC & custom multipin connectors (triax).
- Firewire (a.k.a. IEEE-1394) - a computer bus which
has been accepted by most of the AV equipment manufacturers. You can
squeeze DV down a firewire conection.
- USB (universal serial bus) another bus now more commonly found than firewire
- SDI (Serial Digital Interface) Found on high-end
digital video devices. Can include embedded audio along with the video.
- HD-SDI - The high-definition version of the SDI digital interface.
- HDMI - High-Definition Multimedia Interface. Carries audio. (DVI-D, a computer display connector is partially compatible with HDMI but carries no audio.)
- AES/EBU (AES3) Developed by the Audio Engineering Society and the European Broadcast Union. Typically uses 3 conductors with XLR connectors. Found on professional gear.
- S/PDIF (Sony / Philips Digital Interconnect Format) - Can be transmitted over coaxial (2 wires) or over optical (TOSLINK). Mainly found on consumer gear.
- TOSLINK (Toshiba Link) - Fiber optic.
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