Your video masterpiece is complete. You shot and edited it on a high-band format such as Hi8 or S-VHS. You cut no corners when you made this one; you did everything by the numbers. All along in the back of your mind was the desire to win an award in some prestigious national video festival.
Now that the editing is finished, it’s late at night. You’ve had too much coffee to sleep; you see visions of yourself accepting that coveted award. You flip on the TV. There’s that gawd-awful infomercial you’ve endured countless times. This time, you watch from the director’s perspective. The content stinks, but the lighting is good; camerawork–good; picture quality–great! In fact, the image looks a hundred times better than yours. It’s not only sharper, but smoother, less jumpy, with crisper edges.
As you nod off in front of the television, images jump in your head–the infomercial, the jagged edges in your video, the security guard at the Academy Awards kicking you out. You cross a snowy bridge ready to throw your camcorder into the chilly water.
Then your guardian angel appears and whisks you away to a lovely video store with giant monitors showing your video as smooth and clear as the infomercial. Below some of the monitors are sleek and narrow boxes with the initials "TBC" on them. Some monitors receive signals from Macs, PCs and Amigas.
The angel then shows you the largest monitor where you see yourself receiving the Academy Award for greatest videomaker. "How did you get there?" asks the angel.
And then he answers himself. "Before editing your video, you purchased one of these." He points to the sleek boxes and computers near the monitors. "You bought one of these magic boxes, the digital creations that turn camcorder tapes into broadcast-quality images. You bought a TBC!"
What’s a TBC?
You beam with delight as your angel continues with the explanation. He tells you how the copies of your previous videotapes had jagged edges in the picture, and how a time base corrector fixes this by redrawing video scan lines for perfect alignment. The gentle angel reminds you that videotape stretches easily and creases when it runs through worn-out VCR components. That’s what causes the scan lines to get out of alignment, resulting in jagged edges and sometimes even complete breakup of the picture.
"But what about that shot I had to use from Uncle Charlie’s camera? That scene was jumpy; it’s stable now?" you ask.
The kind angel replies that yes, the TBC stripped off the old sync and added new sync information to stabilize the picture and eliminate the jumpiness.
"And that shot was a little green," you continue in astonishment; "now it has perfect color!"
The patient angel adds that your particular TBC had a built-in proc amp (processing amplifier) that let you adjust your colors on your videotape copy much the way you do with a TV monitor. The angel reminds you too look for the proc amp feature when you’re shopping for a TBC, because not all of them have it. You beam with delight and wake up with a grin on your face.
How It Works
A time base corrector is a device that digitizes each scan line of video, stores it for a very brief period of time (microseconds) and then releases the line of video at a precise time. Since videotape is flexible and, as we said, subject to stretching and shrinking, it may not display each scan line at the precise moment. This "time base error" shows up as jagged edges on the images and a subtle shaking of each scan line. When the time base error is really bad, it can cause a complete loss of sync and an unwatchable picture.
The more sophisticated TBCs also have digital video noise correction. Some even have comb filters that maintain the image’s original sharpness. TBCs that include a processing amplifier (proc amp) allow control of color, brightness and contrast. TBCs with a built-in synchronizer can lock onto virtually any video signal, including those from consumer VCRs.
When You Need a TBC
While you may not have tapes with true time base error, the sync replacement feature of a TBC may be reason enough to purchase one. Tapes shot in the slow EP speed, or tapes that are second- or third-generation copies may not have stable sync; copies may be very jumpy, or the images may flop and roll. The new sync signal that the TBC provides can restore stability to nearly unwatchable videos.
If you wish to use a video switcher that doesn’t have built-in frame synchronizers (such as NewTek’s Toaster), you’ll need a TBC for each source VCR. However, you may not need a TBC if you use video mixers like Panasonic’s WJ-AVE7 or Videonics’ MX-1, because they come with built-in frame synchronizers to keep your transitions in sync. (See sidebar on video mixers with synchronizers.)
Getting Started: TBCs on Computer Cards
To fill the demand for low-cost TBCs, several manufacturers have produced TBCs on cards that plug into PC or Amiga computers. These newly developed boards are TBCs complete with synchronizers and a proc amp. Most board-level TBCs let you adjust the proc amp controls with your mouse, but some offer a more convenient remote control. Since they use your computer mostly as a power supply, the right kind of computer is all you’ll need to operate them. Unfortunately, no TBC cards are made for Macintosh computers, but that may change in the near future.
For $800 list, you can get I.Den’s TB Card II. It comes with a remote control and has Y/C input and output connectors. Y/C video processing is used with S-VHS and Hi8 formats to achieve high resolution and a reduction of chroma dot crawl–those annoying dots of color that look like red ants parading off your image. Ikon Video in Santa Ana, California distributes I.Den’s TBCs.
Digital Processing Systems (DPS) makes the TBC-III, a card with software that goes for $850. It includes a mouse-controlled proc amp and has composite (standard video) input and output connectors. The TBC-III has Y/C connectors for input only; the output is composite. If you edit onto an S-VHS or Hi8 record VCR, spend a little more and get their TBC-IV ($999) with Y/C outputs as well as inputs.
Prime Image makes the model PCB with proc amp as well as Y/C inputs and outputs for $950. Feral Industries offers their LC 4:2:2 TBC on a card for $975 with a proc amp and Y/C inputs and outputs.
Feral also has a more advanced TBC that includes a comb filter for sharper pictures. The Feral Model A 4:2:2 lists for $1395. Nova Systems also has a card with a comb filter–the Nova Mate, which lists for $1400.
Rack-mount or Stand-alone TBCs
You may not want to have your TBC on a card. For example, if you want to move your TBC from your edit room to your duplicating room, a stand-alone TBC may be more convenient for you. You can mount stand-alone TBCs on a standard component rack, or they can just sit on a shelf. They sometimes have proc amp controls on the front panel for color correction, and some stand-alones include fade to black and freeze frame.
Digital Processing Systems makes their model 235 stand-alone for $1995 without a comb filter. For-A makes a stand-alone model FA100 with Y/C inputs and outputs but no comb filter for $2195. Feral stand-alone units generally cost $595 more than their board-based TBCs.
Hotronic makes a stand-alone TBC, the AP41, for $995. It has front-mounted proc amp controls as well as freeze frame and strobe. It has a Y/C input, but only composite outputs. For $1250, you can get their AP41SF with both Y/C input and output. Comb filtering added to all of this is available in their AP41SP for $2200.
Hotronic’s new low-priced AR31 ($500) includes proc amp controls, genlock, an adaptive digital comb filter and many other high-end features. With Y/C inputs and 500 lines of resolution, it’s sure to turn some heads in the consumer and prosumer markets.
Dual-channel TBCs for A/B-roll Editing
The next step up is the dual-channel TBC. In order to perform A/B-roll transitions (dissolves, wipes) from taped video sources, video signals from the source VCRs need to be synchronized with each other. In order to accomplish this, you can stack two stand-alone TBCs, use two TBC cards in two separate slots in your computer or purchase a dual-channel TBC.
The Kitchen Sync from Digital Creations is a dual-channel TBC that lists for $1395 and includes a dual remote control unit. For an additional $99, you can get their Y/C option; another $150 gives you genlock capabilities, so you can synchronize the TBC to industrial and broadcast VCRs that require external synchronization.
Digital Processing Systems makes the stand-alone dual channel TBC-III ($2295) and the dual-channel TBC-IV ($2585). Each of these comes with an external remote control. Feral offers their LC 4:2:2/2 stand-alone dual TBC for $2565.
I.Den makes the IXT-77 ($4495), a dual-channel TBC that includes transcoding between Y/C and composite, as well as a comb filter.
Digital Effects in a TBC
Since TBCs digitize the incoming video, it’s really a snap to include digital effects. In fact, TBCs with effects used to be more plentiful before the advent of computer-based all-in-one SEG units like the Video Toaster.
So you might think, "Why pay the extra money for a TBC with effects?" One reason is that the effects that the Toaster and some of the other video mixers produce will often diminish the quality of your image. For example, a very common effect is a small picture-in-picture image over the shoulder of a newscaster. Toasters and mixers that perform this effect often produce a somewhat unclear, pixellated image.
Enter TBCs with effects. While not trying to compete with sophisticated digital effects generators, some manufacturers provide TBCs that include the particular effects they can do well.
Feral makes a TBC model called their model E 4:2:2, which runs for $1595 on a card or $2190 as a stand-alone unit (the E 4:2:2/1). This TBC lets you shrink the image and place it anywhere you want. You can then put your shrunken image over a colored background or over a background with text. To perform the picture-in-picture effect where the smaller image combines with the larger, you will need to add in their E 4:2:2-C combiner ($495 extra). Or you can purchase both together as the E 4:2:2/1C ($2685).
TBC Remote Controls
We mentioned earlier that one of the great features of TBCs is the proc amp for color and brightness control. Most TBCs on a card let you manipulate these controls using your mouse. You simply click on electronic "buttons" on the computer screen to manipulate the color information of the image.
A more convenient way to adjust the proc amp is with a remote control box, included in some of the above TBCs but optional on others. The remote control lets you turn standard knobs–a little faster and certainly more intuitive than mouse-controlled proc amps. Many of the board-level TBCs let you add a remote control to them as an upgrade.
If you bought one of the Digital Processing System’s TBCs, model III or model IV, you can add the RC-2000 remote for $299. Remote control units for Feral TBCs cost $350-395.
Transcoding and Component Adapters
Earlier, we discussed composite and Y/C video processing. A composite signal runs through the standard video connector on VCRs, while Y/C will add to the resolution and color purity of S-VHS and Hi8 tapes.
Most TBCs we listed have both composite and Y/C connectors, but if you use a composite input, you have to use a composite output. They don’t transcode. Transcoding lets you mix inputs and outputs while allowing you to take advantage of the Y/C features at the output stage.
A transcoding adapter on your TBC works well when using a Toaster together with S-VHS or Hi8. The Toaster has only composite inputs and outputs; the transcoder will let you maintain the benefits of S-VHS or Hi8 and still use the Toaster.
Nova makes the NovaMate XT transcoding TBC for $1450 on a card or $2130 as a rack-mount unit. I.Den makes the IXT-7, a stand-alone transcoding TBC with a comb filter for $2495. The I.Den IVT-7 is a stand-alone transcoding TBC for $2630. And Feral’s transcoding TBC, model A 4:2:2/T1, costs $2390 and includes standards conversion (more on that later).
If you’re working with Betacam or MII tape formats, you’ll need a component adapter if you want to take advantage of the RGB component recording quality of these broadcast VCRs. Prime Image makes the XPON plug-in TBC with component and Y/C for $1650. Nova makes a component add-on adapter for their TBCs, the model NC-1 for $1000. Digital Processing Systems makes a complete stand-alone component TBC for $2995. I.Den’s IVT-9+ is a stand-alone TBC that transcodes between composite, Y/C and component for $4500.
We have talked about how TBCs stabilize pictures, improve the color and even reduce video noise. But some go a step further and remove the annoying white horizontal streaks that occur when the oxide on the tape gets a little scratched. Video professionals call these streaks dropouts, and some TBCs have dropout compensators that cover up that streak with a line of video. To get this level of sophistication, you’ll have to pay considerably more than you would for a basic TBC.
Digital Processing Systems offers their Model 220 stand-alone TBC with a dropout compensator for $3495. JVC makes a TBC with dropout compensation–the model F250U ($3950). Another stand-alone unit is the For-A model 510 with digital noise correction for $4700.
Standards Conversion with Your TBC
Since TBCs digitize the incoming video, they can also modify the signals for international television standards. When you send copies of your masterpiece to other countries, you’ll need to convert them to the appropriate standard, such as PAL or SECAM.
Several TBC manufacturers offer add-on cards for standards conversion. Prime Image makes their model XPON-TBC that combines all the functions of a TBC and converts tapes to and from PAL (but not SECAM). It costs $1650 for the basic card, plus $295 for an optional remote control. Another $499 gets you the optional comb filter.
Feral makes their A 4:2:2/T1 TBC that converts between American standard and PAL tapes. This stand-alone unit includes a proc amp and a comb filter for $2390.
A TBC in Your Future?
Though our hero’s guardian angel has helped him decide on just the right TBC for his video setup, your own decision may take a little more thought on your part.
First, decide if you can get by with a TBC on a computer card. If your computer is available and you don’t mind using a mouse to set colors, you can save a lot of money with a board-based TBC.
If you plan to perform A/B-roll editing, you’ll need two TBCs or one of the dual TBCs we mentioned. If you have some equipment with Y/C connectors and some with composite video connectors, a transcoding TBC may be a good investment.
Then comes the hard part. You’ll have to decide if the increase in quality warrants the extra cost of a comb filter. Will you really use the special effects available in some TBCs? Do you want to use your TBC to convert tapes to international standards?
These are all questions that you can answer by determining your needs and evaluating the products on the market. Unfortunately, only a few cities have industrial video dealers that will display various TBCs, but some mail order suppliers might let you try one model and trade it in for another.
TBCs are a good investment; consider getting a good one. Unlike VCRs and camcorders, TBCs have no moving parts to wear out. Even though they’re digital devices, the technology doesn’t change that much from year to year, so you don’t have to worry about obsolescence.
One thing is certain: a TBC will certainly improve your image. And that’s something every videomaker is interested in.
SIDEBAR: TBCs and Synchronizers in Digital Video Mixers
Videonics incorporates a dual-channel TBC in their MX-1 video mixer. While it doesn’t have the sophistication of some of the TBCs discussed here, it does provide frame synchronization so you can mix the output of two VCRs to perform A/B-roll editing.
Other digital video mixers (such as Panasonic’s WJ-AVE7, MX-30 and MX-50) have frame synchronizers that allow A/B-roll editing, but do not have a true TBC to correct time base error.
SIDEBAR: VCRs with TBCs
VCR manufacturers include TBCs in some of their editing VCRs so that videomakers can edit and copy their tapes as cleanly as possible. Some high-end S-VHS editing VCRs offer optional plug-in TBC cards. Betacam and other broadcast VCRs have included TBCs for some time. Now, manufacturers of consumer VCRs have started including TBCs with their machines. While these TBCs improve stability and remove jagged edges, they usually do not include a proc amp or a frame synchronizer. You’ll need an external TBC if you want to sync two VCRs to work with a non-synchronized switcher, such as a Toaster. Panasonic’s consumer-grade PV-S4480 ($1099) includes a simple TBC. Their AG-1970 ($1940) is a semi-pro editing S-VHS VCR with a similar TBC; even their AG-3 camcorder ($3570) comes with a basic TBC. On the Hi8 side, Sony makes the EVS-7000 Hi8 VCR ($1999) that includes a similar basic TBC.
SIDEBAR: The Jargon of TBCs
Comb Filter: An electronic device that reduces video noise by lowering contrast.
A technique of dividing the video signal into red, blue and green portions of the signal, each having their own input and output connector. Component processing exists on Betacam and MII VCRs.
Standard video going in or out of RCA-style connectors is composite. This is slightly lower quality than Y/C or component processing.
Dropout Compensation (DOC):
When normal wear and tear scratches the oxide away from videotape, dropouts (brief, white horizontal streaks across the picture) occur. A DOC replaces that streak with a previous line of video.
A field is one half of the video image, displayed in 1/60th of a second. A frame is the full image, displayed every 1/30th of a second. To freeze a picture in motion, you generally use field freeze. Frame freeze is higher quality, but may not be rock solid if there is movement in the image.
The ability of equipment to be synchronized by an external sync generator.
Video noise shows up as grain or dots on the screen. Digital noise reduction (DNR) reduces this.
Pronounced "prock amp", this term is short for a processing amplifier that adjusts color and brightness on videotape. Many TBCs have them built in.
Some TBCs that are stand-alone units (those not on a card) have tabs on the front plate that allow them to be mounted permanently in a professional rack. Some do not.
The ability to copy tapes between the American television standard (NTSC) and standards in other countries (either PAL or SECAM).
Some full-frame or infinite window TBCs have a built-in synchronizer to lock up two or more VCRs for A/B-roll editing.
A feature in TBCs that allows translation between Y/C video and composite video. More advanced TBCs include component transcoding.
Used with S-VHS and Hi8 VCRs and similar to component processing, Y/C separates the luminance or gray scale portion (Y) of the signal from the chroma or color (C) portion, and uses a special 4-pin cable to keep them separate. Y/C video is also known as "S-video".