[originally posted July, 2017]
A Common Video Preservation Scenario: A researcher requests a copy of a show held in your special collections. It’s a university production from the 1970s, a unique recording on ¾” tape. This tape is an “at-risk” item, because the inherent vulnerabilities of magnetic based media. What do you do? Do you send it out to a vendor, or do you digitize the tape in-house? Where possible, it’s best to digitize at-risk items in-house. It’s faster, it’s more economical over the long-term, and you can maintain your own quality-control standards.
AV preservationists have spent un-countable hours of our lives discussing the best capture format for analog video preservation. But actually… how you send the signal from the deck to the computer’s capture card is the most important aspect of digitizing analog video. You can capture 10-bit 4:2:2 anything, but the quality of what you’re capturing is linked to the signal you’re sending. So with this fact in mind, this post will describe the necessary equipment and guide you through the basic setup required for digitizing your at-risk analog video in-house.
One of the biggest issues that defines magnetic media as “at-risk” is obsolescence. It’s quite difficult to find and maintain the device needed for analog video playback. Prepare to spend some time digging around online or contacting potential dealers to find a functioning playback device. A good place to start looking for old, obsolete AV equipment is the on-campus video production house. They might have old gear hanging around! Or a local television station may have gear to donate to your archives. Be creative. You need well-maintained, industry-grade equipment with as much related documentation as possible. Those dog-eared operational and service manuals are invaluable for maintaining the functionality of old gear.
Using correct cables and cabling may be the single most important aspect to setting up a video preservation rack. Know your source signal (composite, component, or Y/C ) and send it out using only the highest-grade shielded cable. Remember: Shielding reduces electrical noise and…its impact on signals and…lowers electromagnetic radiation. Shielding prevents cross-talk between cables… Shielding not only protects cable but… machinery and people as well. [1] http://www.wireandcabletips.com/importance-shielding-cabling/
PRO-TIPS: Cables, Cabling, and Termination
• ALWAYS use broadcast-quality RG59 BNC 75ohm cables for video
• ALWAYS prefer XLR (balanced audio) cables to RCA (unbalanced audio) cables
• ALWAYS terminate open loops with 75ohm terminators at end of signal loops*
*But be careful! Improper termination can affect the video signal. A double termination can cut the video signal in half, while a lack of termination will overload the video signal. This might be where you need professional help.
CONGRATULATIONS!! You have managed to acquire a professional-grade BVU U-matic deck that supports machine control input. Now you are able to control the deck from a computer via a RS-422 cable, not missing any information at the beginning of the tape. This is good. This is why the RS-422 cable is included on the equipment list.
Now what about the capture card and computer? I like the AJA KONA LHi capture card and AJA KONA KLHi-Box. Together, these will allow for seamless capture of composite, component, and Y/C (for analog signals) and SDI or HDMI (for digital signals). The KONA LHi works well with Premiere CS6, but it also has its own software that captures SD analog video as 10-bit 4:2:2 uncompressed v210. The Kona LHi is also able to capture closed captioning and timecode information. All of these are required metadata for video preservation. The preservation master could have up to five streams of data per file: a video stream, two audio streams, timecode, and closed captioning CEA-608. With newer computers, you’ll have to place the AJA Kona Li capture card in a thunderbolt expansion case and send the digital video signal from the expansion case to computer‘s thunderbolt in.
Now. It’s very important to place a Time Base Corrector between the deck and the capture card. You also need waveform and vector scope connected post-TBC, so you can monitor and adjust the video signal, using the scopes as your measurement tools. For example, if color bars are in front of the program, you can adjust the luma, chroma, black (set up), and hue (NTSC only) levels to get the best possible signal from the tape. Also, I recommend having all equipment ‘genlocked’ to the same reference to ensure picture stability. For SD composite video, it’s called blackburst – a composite signal of black with no picture data. With all pieces of equipment timed and in-sync, or locked to master sync, you increase the stability of your capture.
My preference for signal monitoring is viewing the signal directly off the deck, as well as post capture card. This helps pinpoint where any problems might occur in the signal. For example, if there is visible signal error on the monitor connected at the end of the chain (post capture), but the video looks good coming straight out of the deck, you can focus your troubleshooting on the cables, settings, and equipment either at or after the TBC point. It’s also important to have a cathode ray tube (CRT) monitor in order to view the video signal as it was originally intended. AND it’s best to have a CRT with blue-only, underscan, and H-V delay features. ‘Blue only’ allows you to calibrate your reference monitor with color bars and monitor your VTR noise. ‘Underscan’ allows you to see every scan line in the video signal, and ‘H-V delay’ allows you to check vertical and horizontal sync. These features will help you get the best signal out of your deck and troubleshoot any signal errors.
This brings me to the last piece of gear to install in your AV Rack: a test pattern generator. A test generator helps you check proper signal flow by sending a test pattern, like color bars, through the signal path. You can also use the color bar test pattern to set display levels – like brightness – and contrast to ensure your monitor is properly calibrated.
YOUR EQUIPMENT LIST
• Professional rack*
• Professional-grade decks for each format (U-maticSP, BetaSp, VHS, SVHS, Digibeta, etc.)
• RG59 BNC 75 Ohm cables
• 75 Ohm BNC terminations
• XLR cables
• RS-422 cable
• Time Base Corrector/Proc Amp
• Test generator
• Sync generator
• ADC Patch bay
• AJA Kona capture card
• AJA Breakout box and cable
• Sonnet Echo Express SE I Thunderbolt 3 to full-height/half-length PCIe card
• Waveform and vector scope monitors
• CRT monitor**
• Computer***
• Calibrated computer monitors
* sturdy, does not wobble, and allows decks to be pulled out easily and safely
** preferably one that has underscan, blue-only, and H/V delay
*** preferably with a high-speed processor, minimum 16GB memory and 1TB storage
Well, I hope this was helpful for anyone wanting to build an AV preservation rack for their special collections. In the next issue of AV Club, I’ll be discussing best practice for embedding technical metadata into files for future digital preservation conservators. Cheers!
Library and Archives Preservation 