Archiving Multichannel

Recently we’ve seen a number of proposals from various parts of our industry for methods of archiving sound materials. This is even more important for multichannel than for stereo work, because stereo music releases can be said in a sense to be backed up nearly everywhere: all those thousands of CDs! But for those works where the original is either a multitrack or multichannel representation on the format, it may well be economically important to the future of surround sound to get the analog original tapes or films transferred to a digital medium before deterioration sets in. We’ve discussed that before: oxide shedding and sticky tape syndrome affect tape, and vinegar syndrome affects acetate-based film masters, as well as potential coating problems.

There are a number of factors to consider in coming up with a common standard for archiving. There are multiple constituencies to consider: what may be right for a recorded archives librarian at the Library of Congress may not be right for a Hollywood studio. The librarian has to be concerned with quality of archiving, it goes without saying, but cost of equipment, supplies, and transfer labor is a very strong ingredient in decision making for these uses. The Hollywood studio has some of the same cost concerns, because their libraries can contain millions of reels of film, but the balance of factors may be a little different. Of course, one hopes we can achieve economies of scale through use of common formats across many disciplines, but the requirements list is pretty long, and the balancing act among the requirements might make complete commonality impossible.

Another issue to address is obvious: the obsolescence of formats. An organization that stays ahead of the game tends to adopt new formats, only to see them potentially made obsolete early. An analog example of this is the National Film Board of Canada, which early on built a stereo Nagra out of two mono Nagra III’s! Talk about ahead of the game. With two sets of staggered mono heads to make and play stereo recordings, the resulting tapes were not interchangeable with stereo ones when stereo machines became available. I visited there some 15 years ago and saw a machine room that was a history lesson in recorded formats: Fairchild sync, Rangertone, etc., and all were still working! One each for every format known to man….

The same idea applies to digital formats, too, and with the pace of development even greater than in the analog era, the obsolescence factor is even stronger. The Web site contains information about eleven contemporary digital backup tape formats, and within just one of these formats (AIT) there are already four proposed variations, so we’re talking a family tree here, with many branches. Who will be able to play most of these in 15 years? Here are some thoughts that might want to be factored into decision making in the future of archival formats:

1. I, for one, simply do not believe that the ultimate device for storing digital data for archival purposes is going to be tape based. Today the following statement is true from the point of view of computer experts: “The traditional security backup technology — tape — remains the best choice, and for two very good reasons: capacity and cost. The more inconvenient a security backup regime is to implement, the less likely users are to bother. With the size of the average hard disk now several gigabytes, tape is generally the only media that allows a complete hard disk to be backed-up without needing to swap media during the process. Furthermore, removable storage media is comparatively expensive, with overall costs up to ten times that of tape.” However, this still leaves the storage on linear tape, which has the following problems:
a. Tape has potential problems due to mechanical tape damage. Magnetic reading requires contact due to the extreme spacing loss that otherwise occurs, so it is subject to tape guides, heads, capstans, and other objects in the path.
b. Tape has potential coating problems. While the tape oxides for backup purposes are fairly different from audio ones — containing less or no binder for example, exactly for the reasons that we are moving to digital in the first place, there are still potential problems. One system claims a 30-year life expectancy. Is that good enough? It should be if the library is periodically reviewed and updated, but wouldn’t you think of archival medium as having a longer life than that?
c. Tape is accessed linearly, when we know that just about every system in the world today is going nonlinear, for better access. Who wants to search through miles of tape to find something near the end?

2. Factoring in the above, I believe that the ultimate storage mechanism is going to be optical. That’s because there is less to go wrong in reading an optical medium: you need no contact, there is less handling of the medium, and nonlinear access is possible.

Today’s generation of CD-Rs doesn’t qualify. The life is not long enough; early failures are well known. But an optical medium based on a substrate of known stability, with a known technology of recording optically on it, will do the job. Where’s that? Silver on glass images of the Civil War are still with us from Matthew Brady. The soft coatings of his time did have problems. There can be unforeseen chemical reactions going on across time. But nonetheless one of the most stable of things known to man is the deposition of silver images on a glass substrate. Extensive testing with accelerated life and environmental testing would have to be used to prove a new medium’s efficacy, but the requirements are all well within reach, and without the application of exotic and unproven technology.

3. The second ingredient after the physical recording layer is the “wrapper” for the actual audio. In today’s newly minted terms, what we would call the program audio has been renamed “essence.” Don’t ask me why. Accompanying the essence are wrappers, including metadata. Metadata, properly used, accounts for all the dozens of items that we have to tell the end users about our multichannel recording: the session notes go here, the timecode, the track layout, etc. Metadata is effectively stored with the audio to prevent its being lost and to label everything present once you have the medium in your hands. This solves the problem, brought up elsewhere, of how to label things, what kind of labeling scheme to use, etc.

4. Finally, there remains the question, how do I read this format in the future? Communicating with a distant future, especially a future operating system, is a little like dealing with aliens! After all, Arthur C. Clarke said that any sufficiently advanced civilization will have technology indistinguishable by us from magic. The other side of this coin is, “How is an advanced operating system of the future going to understand what we were up to, when supposedly what we are doing is so primitive?”

The idea should be to leave lots of hooks around, ways into the system and understanding it: what constitutes essence and how it is recorded, what metadata, and what error correction. This problem was faced by the scientists who put Pioneer 10 on its long route into space in 1972. They came up with a universal way to describe the conditions of the spacecraft you have in your hands, and that’s just what we need from our systems today: to leave around enough information to be able to decode them under any conditions in the future.

5. The power of error codes should not be overlooked. Use of the Reed-Solomon code made the compact disc a usable medium from the laboratory curiosity that preceded it. While no one wants to spend a lot of bits on error protection, this is an application that can’t be too well protected. With the growing capacity of all media, exactly how much overhead error correction adds will not be too much of an issue in the future, so let’s design even more powerful ones than we’ve got, so we always can get back to the original data. Of course, this has to be factored into a scheme that involves geographic dispersal of materials, proper storage conditions, cataloging, and probably other factors to consider that we’ve built a literally bombproof system of keeping sound materials for future generations.

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