T356 - Spring 2008 - Week 6

Agenda/reality check

• 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
• Then the performance piece and then the PSAs.

PSA Reality Check - We should schedule PSAs in the next few weeks. Please find out if your client/talent has a preference and bring that to lab. (Every team will get a half-hour block) If you don't have a preference, we'll simply block it out to try to group all of the projects with similar production treatments.

Demonstration videos. I've already distributed groups and schedules last week. We can review these in lab this week. You should meet with your members and iron out any loose ends as 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.

Studio Equipment

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 and setup.

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.

Waveform Monitor

A device used to examine the luminance portion of the video signal and its synchronizing pulses.

• Black should register 7.5 IRE on a waveform monitor (US NTSC)
• ATSC/Digital black levels should be 0 IRE
• White level (both NTSC and digital) shouldn’t be any hotter than 100 IRE on a waveform monitor

Vectorscope

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

Sync generator

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.

Switchers

Video switchers allow the user to select and mix video signals. They also provide a limited degree of effects.

Basic functions:

1. Select appropriate source from several inputs
2. Perform basic transitions
3. 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 bus
• Effects bus: used to select sources for different effects

Basic Operation:

• 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 between sources)
• 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 various switchers

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. Our Grass Valley switcher doesn't have the accessory module allowing us to do this. DVEs can include perspective, mosaic, solarization, 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 keys, 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 colors are usually farthest away from the color of 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 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, etc.

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 applications.

• Production switchers (used for live production-like the Grass Valley in Studio 5)
• Post-production switchers (used for primarily for editing) Most of the functions can be remotely controlled by the Editing Control Unit.
• Master control switcher: computerized. Control VTRs and video cart machines.
• 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 memorize a variety of setups.

Electronic designs: composite, YC, RGB, color difference, digital etc.

Analog/digital switchers: look & operate almost the same way

Audio follow video switchers. Controls an automated audio mixer so that the audio follows the video.

Video Recording Systems

Tape-based (uses videotape) Analog or digital. They both function the same way.

Disk-based (uses computer disks) can either accept digital video or must be able to digitize the video.

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 & BNC
• 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 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 DVD players and projectors.
• RGB (true component) The Red, Green & Blue signals are kept separate. Not as common as the color difference system. Connectors: BNC & custom multipin connectors (triax).

For digital video you can use:

• 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.
• 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.

 

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