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Stress and Strain
Tape under threat
Managing metadata

Tape Unravelled

by David Fox

Is there still a future for tape? Manufacturers go head to head. Plus a guide to who makes what.

Despite the rise of disk recording, tapes are still the bedrock of TV production. Used and abused by everybody, often in extreme conditions, stored for years, and still expected to deliver a picture. The ideal tape is small, yet has a huge capacity, is engineered to survive almost anything, yet doesn't cost much. Surprisingly, most modern tape formats manage this (even if they occasionally have to draw on the powers of digital error correcting VTRs to save their embarrassment).

Anyone following the Guild Of Television Cameramen's online forum recently, will have read about the difficulties some Digital Betacam users are having trying to find out why their camera heads are wearing out prematurely - is it because the tape is too abrasive, or is the head at fault.

In this particular case, investigations continue, but in the past, Maxell's Ceramic Armour technology has been accused of increasing head wear. Then, independent studies proved that "premature head failure was down to incorrect or uneven projection of the head tips on newly introduced small head drum cameras, which caused a head touching problem after around 400 hours of use," says Andy Houghton, engineering & technical support manager, Maxell Professional Media Products Group.

Besides, "abrasion is not necessarily down to the 'hardness factor' of the material, but down to the 'co-efficient of friction'," he says. To achieve hardness and durability, but reduce friction, Maxell uses "a very stable Ceramic Armour metal particle which is harder but more protective than other types," coated in special lubricants and highly polished, which, he claims enable one broadcaster he knows achieve more than 3,000 hours on DVCPRO cameras.

DVCPRO is metal particle (MP) where the individual iron particles are coated with an anti-oxidant to protect from oxidation. DV/DVCAM is metal evaporated (ME) were the iron is evaporated on to the base film and not bonded to the tape like MP. "This process can leave an abrasive surface to the tape, requiring not only a protective layer against oxidation but also a lubricant layer to help in head-to-tape contact. Damage to these layers can cause loss of quality and lower head life," claims Rob Tarrant, product marketing manager, Panasonic Broadcast Europe. He believes MP is also a longer-lasting formula, making it more suitable for archiving, and points out that DVCPRO has the additional advantage here of being one-seventh the volume and one-sixth the weight of equivalent half-inch tapes.

However, Panasonic's latest Master Grade DV tapes use an improved ME formulation, using a new evaporation technology called S-AME (Super Advanced Metal Evaporation) that improves the videotape's magnetic density by 400% over previous Panasonic DV tapes. Its main advantages are: higher output power; low head wear and reduced head clogs thanks to a dry-type lubricant; and improved performance in severe conditions.

Fuji doesn't make ME tapes, because it believes it is not as durable as MP. It is also more difficult to manufacture. Instead, it uses technology which simultaneously coats two layers: a non-magnetic bottom layer of ultra-fine Titanium Fine particles and a magnetic top layer of high energy metal particles that is of a sub-micron order of thickness. "The result is dramatically reduced self-demagnetisation loss for outstanding high frequency output, which in turn makes it possible to achieve higher recording densities than are possible with conventional coating techniques," says Richard Pun, senior sales manager, Motion Picture & Professional Video Division, Fuji. He claims its high density capabilities and electromagnetic properties are equivalent to ME, but "much more robust and stable."

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"Tapes with a high generation of powder debris need to be abrasive to keep the heads clean. This gives a high head wear and increased maintenance costs. The Sony policy is to develop tape with a low generation of powder debris which does not require high abrasivity to keep the head condition in order," says Shin Ishikawa, marketing manager, Professional Media, Sony Recording Media and Energy of Europe.

"All videotapes are purposely formulated to have some abrasion, without which tremendous head clogs will occur and cause dropouts and high errors," says Pun.

"The abrasivity of the tape surface is carefully formulated to have just enough abrasion to enable the tape to have a self cleaning effect on the pole-tips of the heads without it being too coarse to wear out the heads too rapidly. The governing factor for abrasivity is the amount of lubricant added to the mixture for the tape coating. Too much will make the tape surface too smooth and cause plenty of head clogs and also make the tape sluggish under low temperature operation so our engineers have to work out exactly how much to use," he adds.

"When tougher formulations of tape started to appear back in the 1980s there was a conscientious move to develop new head formulations to match them, including a move away from Sendust to Polycrystalline gap-less tips (by gap-less I mean filled with glass and/or some other hard wearing substance). This was to take advantage of the increased electrical performance of the tape, and to make the heads last longer as they were becoming (in the new segmented format multi-headed drums) more difficult to replace. Let's not forget that if you got 500 hours out of a quadruplex head on a two-inch machine you were doing very well (but you could replace them quite easily)," says Colin Green, JVC product manager for D9 and Professional DV. Today, "you are doing badly if you only get 1,500 hours out of a mains machine."

He claims JVC has made more of the head to tape relationship than most manufacturers. D9 had a rotating centre drum (with fixed upper and lower drum mechanisms) from the start. "This means a much lowered tape tension and stiction (what happens when the tape wraps around the head drum) characteristics so tape wear on the head is minimised, tape damage is minimised and better linearity (track straightness) is maintained so assuring long head and tape life. Currently we are quoting about an average 5000 hours head life for a D9 unit with the current record in the States held by a Fox News unit which has broken the 15,500 hour barrier." During EBU/SMPTE Task Force tests, a D9 unit had the head change time verified at under 45 minutes. It also tested the tape, which achieved over 500 passes in a continuous record/replay sequence with virtually no increase in error rate.

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Stress And Strain

Houghton says many head wear problems are due to the format being used. "The amount of tape tension can vary between various formats, the humidity and temperature can also greatly effect VTR head wear and also the application, for example, does the VTR run mainly virgin tape or used tape with more than a couple of passes?"

He points out that tape has to withstand enormous stresses in operation. Component digital VTRs can have more than 20 heads rubbing the tape at any one time at high velocity. Also, "the formats are getting smaller, thinner and yet are still expected to perform the same as larger formats did."

"One of the most crucial factors is head-to-tape matching. When a manufacturer of a format lays out the specification it is not done lightly. Poor performance can result from not adhering to those specs as tightly as possible. Having a tape formulation which has better Coercivity figures than its nearest rival is a poor substitute for a tape formulation binding which destroys the heads in rapid time," says Green.

"Most formulations now include things like dust-proof shell casings which prevent ingress of dust and dirt onto the tape exposed at the front of the cassette when outside of the machine, plus interior mechanisms designed to even out spool packing and tape movement over tight corners," to improve robustness, he adds.

"Basically the wider, thicker and stiffer the tape, the more durable it is. A wider track pitch, combined with the magnetic material and the bonding used, makes a more reliable recording. These factors made tapes vary large and cumbersome to handle," (such as a D1 or D5 2-hour cassette), says Tarrant. Thanks to technology advances in the base film and magnetic material, the latest tape formats are smaller and thinner. But, "the same factors are still important. Take thickness; DVCPRO is 8.5 microns whereas DV/DVCAM is 7 microns. This may not sound a lot but it makes DVCPRO 1.8 times the strength of DV/DVCAM tape."

Green maintains that it isn't just a high packing density that is important, but also the uniformity and durability of those particles. And if there is drop-out or tape damage, digital VTRs should include Reed-Solomon error protection coding to recover lost or damaged data. "This is why digital formats are on the up. Output performance stays good right up to a point way beyond when an analogue format would have given up the ghost. However, the biggest rise in error rate is caused by large numbers of small random errors (rather than bigger burst errors caused by tape damage). We've included additional circuitry, like Viterbi detection, in our Professional DV range which effectively halves that error rate, giving even better assurance of output pictures on replay," says Green.

JVC's Mini-DV tapes have a DLC (Diamond-Like-Carbon) protective layer and special surface treatment to give better performance for its Professional DV camera range. Sony uses new MP++ metal particle technology boasting "increased recording density, low error rate and good archival stability," for its DVCAM and AIT formats, "which increase performance and reliability in spite of narrow tape width," says Ishikawa.

However, for news at least, little of this matters if the pictures are newsworthy. Green cites the light aircraft which landed in Red Square and the only footage was on VHS-C, so the news organisation he worked for bought it and sold the story on the European distribution circuit for £30,000 a time.

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Tape Under Threat

With the rise of disk systems, such as Ikegami's EditCam II, JVC's new DV-compatible HDD camcorder and Sony, Philips, Panasonic and others developing DVD-based systems (even if a high quality system is a few years away), will tape still be the best choice?

"Tape isn't finished yet," insists Houghton. It is "much cheaper, stores very high capacities, is time proven to archive well under good conditions and a very flexible [highly portable] format." Although hard disks are getting faster and storing higher capacities, he says they are not as reliable, not removable for cleaning, and wear out easily.

Maxell does make optical disks, but these have disadvantages in capacity, data transfer speed and, he jokes, fall victim to European operators who smoke too much. However, they are light, easily transferable from one machine to another, archive longer than magnetic tape, are cleanable ("including that cigarette smoke"), and giving higher capacity thanks to finer track pitch and new laser technology. "There is the possibility in the future to read and write multiple layers of data onto the disk at high speeds, making optical disks faster in transfer rates and extremely high capacity, he says. Maxell's researchers claim that soon "we will be achieving Terabytes of storage from 5.25-inch disks at very fast data transfer rates."

"Magnetic tape [still] has the superiority both in capacity and cost. However disk recording systems have the superiority in the accessibility," adds Ishikawa.

"The beauty of MiniDV is many fold, but one of these best appreciated when you want to buy something to record on at Lagos Airport and they are right out of 2.5-inch high density hard drives," says Green. JVC see its HDD system as "complementing the tape system, not in direct competition to it. Disk has a number of advantages such as retro-loop recording, random access, and no digitisation necessary, but there are downsides." He cites Ted Taylor [ex-ITN, now Panasonic] speaking some years ago about a disk based camcorder he was testing for news and asking "'would you give a box of ten tapes or ten disk packs (at £2000 a go) to a news cameraman before he disappeared out on a job?' Maybe this will change when blue -laser technology is commonly available and re-writable DVD discs can record Intra-frame 4:2:2 pictures at reasonably low compression rates," he says.

Tarrant believes it will be several years before disk systems make any headway in ENG and general production. "If a higher quality is needed like DVCPRO-50, DigiBeta or even HD, then these systems in a camcorder style will not be around for a considerable time. The cost/performance of tape is a hard act to follow," he says.

"With the use of servers for transmission, new DVD disc camera systems emerging and the development of multi-layer disc formats (such as the Fluorescent Multi-layer Disk capable of 140 Gigabytes storage on 120mm CD sized disk), the future requirement for tape will be much reduced," says Pun.

He acknowledges that tape will still be used for archive, "as it is still the cheapest and proven medium for long term storage whereas disk formats have not been around long enough for the long term storability to be proven yet."

Tapes stored in proper, dust free, controlled conditions (with rewinding once a year) should not deteriorate for many years. "The main difficulty is to be able to have equipment to replay the programme as tape formats change fairly rapidly," says Pun.

"Most of the newer digital formats have a relatively high coercivity [of at least 1500 oersteds] and as such are not affected by external magnetic fields," he says. As a field greater than twice the coercivity is required at the tape surface to completely erase the recording, a magnet even a small distance from the tape will have very little impact. "Unlike films the recorded image does not deteriorate and the colour should not fade or alter provided that the tapes are stored under [suitable] conditions. If equipment is available to replay the recorded format, the storability could be almost indefinite," he says.

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Managing Metadata

Data tapes can cope with the new demands of storing metadata, but what about standard video tapes?

Ishikawa believes that such devices as Sony's new TeleFile, which uses a cassette label with a built-in memory chip which can be read by a small scanner, or DVCAM's MIC (Memory in Cassette) which uses a chip in the body of the cassette, are the best ways of integrating tapes into asset management systems and of storing all sorts of metadata, from good shot markers, to GPS location information.

The TeleFile system can easily be updated with keyword and edit information, so that when the tape is sitting on a shelf, someone can quickly locate which tape has a particular shot by sweeping the shelf with a hand scanner.

Tapes already have the ability to store metadata "in the form of auxiliary data space in the video and audio sectors and also in the sub-code area of the digital tape recording," says Green. "We just need the standardisation process to complete before we add in suitable interfaces to access it - if you want interoperability that is (we could produce one tomorrow but it would be proprietary). That way the metadata stays with the material on the tape. Current capacity for D9 is about 921kbps (more than enough to write a small novel about each frame of video)."

© 2000 - 2010

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Tape Manufacturer's - A guide to who makes what (everything from U-matic to DV and D9)
Ikegami's Editcam - a camera that records on a hard drive - not on tape.
Sony's technical info on Metal evaporated tape

David Fox