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What keeps audio archivists up at night?

Wednesday, November 24, 2010 - 05:15 PM

WNYC

Senior Archivist Marcos Sueiro Bal recently attended the annual conference of IASA, the International Association of Sound and Audiovisual Archives, in Philadelphia. He reports on some of the highlight presentations (besides being enveloped by the sounds of the world’s largest pipe organ).

Brecht Declercq | VRT | BELGIUM Large Scale DAT-To-File Ingest and Annotation of Radio Programmes: The Path Chosen at Flemish Public Broadcaster VRT

Digital Audio Tape (commonly referred to as DAT or R-DAT) has many known problems. One of its manufacturers warned back in 1994: "Ampex's position about archiving valuable source programming to R-DAT is simple. We do not recommend it.” Like many other broadcast stations, VRT has lots of DATs: in their case, an estimated 70,000 hours of DAT material, 10,000 of which have been transferred to digital computer wav files along with their metadata.

One way to transfer DAT audio is to use DDS drives and a specialized software such as DATXtract. VRT decided to do it in real-time, with intensive annotation, while listening for errors. Archivists later listen to the wav files and check again for technical glitches, while they add additional subject headings, etc.

Thankfully, Brecht reports only two DATs with complete failure so far (out of 10,000), and that many of the more common glitches had occurred during non-critical sections (e.g. during commercial music playback). Such a low number of failures may be due to the tapes having been originally recorded on high-quality professional decks, and to the tapes having enjoyed ideal storage conditions.

He did not show specific sound degradation results (later I encouraged him to publish results), and found no correlation between brand and deterioration in the VRT Archives. Interestingly, he mentioned how at one point in the chronology of the tapes errors seemed to increase. When he asked a VRT engineer, the engineer mentioned how the technical staff had been cut that year, so tape decks were maintained less frequently; so the errors were presumably recording errors, not errors due to degradation.

He also mentioned that there may be a correlation indicating that pre-1990 tapes are faring worse, but presented no specific evidence. 

He mentioned a RAI study that shows how more metadata increases usage significantly (I have asked him and EBU for the citation).

Careful keeping of metadata (particularly quanitfying error reading) will be important for current and future priority studies.

 

Shane Beers & Bria Parker | University of Michigan | UNITED STATES Hathitrust and the Challenge of Digital Audio Hathitrust is an interesting repository hosted by the University of Michigan, but open to all institutions. For books (which comprise the vast majority of the 264-terabyte collection), it seems to use the ingest standards (“AIPs”) used by Google Books. They recently decided to do a test pilot for audio and found a lack of unified standards. For technical metadata, they are following the upcoming AES schema and Dublin Core, and for preservation metadata they use PREMIS within METS wrappers (METS creation is automated). Their AIP follows Indiana University’s Sound Directions suggestions for best practices. Format validation is done through JHOVE.

 

Stefano S. Cavaglieri & Gabriele Franzoso | Fonoteca Nazionale Svizzera | SWITZERLAND Raising the Quality Bar in Re-Recording Mr Cavaglieri reported measured differences in playback quality (speed accuracy, crosstalk, phase correlation, and frequency response) between a common Technics 1200 turntable fitted with a Shure V-15 Mk IV versus a more expensive model, the SME Model 10 with an Ortofon Bronze cartridge. The results were not surprising, and easily perceived. A similar setup was used to compare standard factory Studer a807s vs those with modifications commonly mentioned on the internet (mostly related to output op-amps). Again, differences were detected; but, interestingly, numbers seemed to show that the factory options performed best.

Four A/D converters were also analyzed: The Apogee Rosetta; an entry-level converter (no longer manufactured) by NOA (probably replaced by this one); the RME Fireface; and the Weiss ADC. Mr. Cavaglieri had little time to show relevant results. Audio analysis was performed using RightMark software.

Feigning despair, Mr. Cavaglieri ended up with a quote from architect Mario Botta about  preservation, in which he claims that the only form of preservation is to let the building fall (!).

 

 Nadja Wallaszkovits & Dr. Peter Liepert | Phonogrammarchiv | AUSTRIA Digitisation of Highly Degraded Acetate Tapes – A Treatment Report

The Phonogrammarchiv in Vienna is no stranger to deteriorating acetate tapes, and some recent projects in that field yielded some unexpected results –for example, the fact that brittle acetate tapes seemed to play back better in a relatively high-temperature and -humidity environment. However, the archive was not quite ready for the shocking state of decay exhibited by a set of recently received tapes from an (undisclosed) country with tropical climate. One tape had shrunk to such a degree that it looked like a disc inside the reel.

Chemical analysis revealed that these tapes were Agfa triacetate, probably manufactured in the late 1940s, but recorded in the 1970s.

Ongoing research at the Phonogrammarchiv suggests that decaying acetate tapes may actually suffer from two parallel processes:

  1. The well-known acetate breakdown known as vinegar syndrome, which is accelerated by heat and moisture;
  2. An evaporation of plasticizers, which reduces the tape’s flexibility and causes it to eventually become brittle.

Interestingly, these highly degraded tapes seemed to no longer suffer from vinegar syndrome, simply because the second process was so advanced that most of the acetate was gone; the tapes were what Ms. Wallaszkovits called “fully cured”.

If the decaying process is truly two-pronged, this could have potential repercussions for the storage of all cellulose acetate materials, including most lacquer discs, since, according to Ms. Wallaszkovits, water can act as a plasticizer and compensate for the plasticizer loss: She pointed out that acetate discs that are in too dry an environment may start cracking earlier.

The Phonogrammarchiv is developing a method to physically restore severely damaged acetate tapes. Although the formula is under development and thus still not public, it will be available once the testing period has successfully been carried out. The results are extremely encouraging, judging by the photographs and audio files presented by Ms. Wallaszkovits, although she pointed out that part of the reason for the high quality of the audio is that it was recorded relatively recently, on 1970s equipment.

In unrelated informal talks afterwards, Ms. Wallaszkovits mentioned that the Phonogrammarchiv is capturing bias information from tapes by digitizing at 192 kHz and splitting the signal. This information can be used to apply later digital restoration processes such as those of Plangent Processes, where easily-detectable fluctuations in bias speed are used to restore the audio signal. The Phonogrammarchiv reportedly is developing (or has developed) a similar process.

Ms. Wallaszkovits also mentioned that they adjust azimuth by tapping a frequency-selective voltmeter to the bias current output. When that voltmeter shows a maximum reading, you have the optimal azimuth. (She also mentioned that in their tests, playback equalization is best applied in the analog domain.)

 

New Attraction: PBCore 2.0 Proposed by: Chair: Karen Cariani, WGBH Educational Foundation Speakers: 1. Chris Beer, WGBH Interactive’s Open Vault 2. Courtney Michael, WGBH Educational Foundation  3. Jack Brighton, University of Illinois  4. Kara Van Malssen, PBS American Archive Project. 5. Katrina Dixon, Northeast Historical Film .

The Corporation for Public Broadcasting’s metadata schema, PBCore, is being revised. PBCore 2.0 should be released January 2011, with significant changes and improvements; they are currently working on their SIP (Submission Information packet) for the American Archive project, and are still open for suggestions. More web resources like http://www.americanarchiveinventory.org, which includes PBCore import/export, will be available in the near future; others include a site for helping with cataloging, http://www.pbcoreresources.org and a PBCore validator, http://pbcorevalidator.org/. Another good resource is http://www.opensourcearchiving.org, a blog on “open source solutions for audiovisual archives”.

 

Tech MD: Is there a Doctor in the House? Chair: Dave Rice, AudioVisual Preservation Solutions Speakers: 1. Kate Murray, FADGI 2. Hannah Frost, Stanford University 3. David Rice, AudioVisual Preservation Solutions.

Technical metadata will be essential for long-term preservation of digital files. FADGI (Federal Agencies Digitization Guidelines Inititative) has suggested a set of BWF guidelines to be used in the so-called BEXT Chunk of archival Broadcast Wave Files (BWF), while Stanford University is working on a successor to JHOVE (JSTOR/Harvard Object Validation Environment), JHOVE2. This is a project from the Library of Congress’ NDIIPP, carried out by the California Digital Library, Portico, and Stanford University, and it uses DROID (Digital Record Object Identification) and the British National Archives’ PRONOM directories extensively. JHOVE2 could be a very useful tool indeed. Another one could be Dave Rice’s metadata aggregator tool, “lovingly called” FATMAP, which can “crawl” a digital collection and mine technical data to present in meaningful ways. As a test, the program crawled the video holdings of the Internet Archive, and the results presented fascinating analysis of the last 20 years of submissions to that web site, plotting the rise and fall of popularities of file formats, languages used, places of submission, and even aspect ratios.

 

Mike Casey | Indiana University | UNITED STATES Strategic Evaluation of Media Collections: The Indiana University Bloomington Media Preservation Survey

The issues faced by Indiana University are faced by audiovisual archives around the world, and are aptly summarized in their media preservation survey. IU is now getting ready to act on the discouraging results. For example, it would take them 120 years to complete reformatting at their current rate. Indiana University is therefore considering “massive, rapid, and considered” reformatting of their media collections. They are hiring a campus-wide Media Preservation Specialist, and have already hired a Film Archivist. IU is now focusing on prioritization guidelines (even evaluating Columbia University’s AVDb), while utilizing parallel ingestion, and creating a repository infrastructure with the help of AVPS.

 

Mr Charles A. Richardson | Richardsons Magentic Tape Restoration LLC | UNITED STATES Rethinking Triage and Preservation of Analog Media Collections

Not without controversy, Mr. Richardson believes that the carbon backcoating of some tapes (not the binder as is commonly thought) is to blame for sticky-shed syndrome (this appears to be at least statistically reasonable). In his view, the common method for dealing with sticky shed (incubating (a.k.a. baking) the tape) contradicts the archival principle of “do no harm”, since tapes do not appear to tolerate repeated bakings well. Sticky shed is after all mostly a friction problem, so much of Mr. Richardson’s talk focused on tribology, the science related to friction. A potentially useful ,if perhaps not very accurate, method to measure friction on tapes involves using a portable Nagra recorder to read the current draw in its meter. Presumably, the more current the recorder is utilizing, the more friction the tape is presenting.

Jim Wheeler of Wheeler Tape Forensics, the original developer of the Ampex patent for incubating tapes with sticky shed syndrome (which, incidentally, technically voided Ampex’s  warranty for the tape because of the high temperature involved) and Jim Lindner of Media Matters mentioned the fact that Mr. Richardson needs to present his studies in a peer-review journal, and give details on his patented system which supposedly “scrapes” the carbon black from the oxide side, and which may also not conform to the “do no harm” principle.

 

Learn more about the conference here.

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Comments [6]

Fuji LTO-6 Tapes from UK

An impressive share, I just given this more share for publicity and want that you continue your articles also on LTO Tapes

http://www.digitaldevicesonline.com/data-media/lto-tapes/p10ddlua00a.php

Aug. 12 2013 01:42 PM
Neil Schubert from USA

Update:
Another tape oven that has worked well so far has been a food dehydrator. I use the type that has no fan in it, just a 100 watt heater coil. These units are perfect for baking tapes, especially those with crayon and sticky syndrome. It doesn't get hot enough to melt the plastic reels, and provides enough heat to get the job done. Run it for 6 hours or more.

You should try to un-tension the tape if possible before using a tape oven. Sometimes this can be dangerous if the tape has crayon syndrome.

So far, this works fine for 1980's wounded birds and wax-off tape (crayon syndrome). It might be more functional than the lightbulb method.

Shipping:

One of the biggest problems I have run into recently involves somebody shipping a reel in a narrow box. It is my suggestion that if you are going to ship a reel to reel tape, that you place it in a film canister, in case it gets packed with UPS truck full of speakers. At least leave at least a foot of packing around each side of the tape. This will allow a buffer zone for magnets. The film canister will provide a shield against high power magnets, like those from an MRI machine. Most tapes make it undamaged, but there is a risk that needs to be evaluated.

Jun. 11 2011 05:57 PM
Neil Schubert from USA

Correction/clarification:

On the previous comment I stated that you should use DBX on the HiFi channels of the VCR. Standard VHS machines are built with DBX or compatible type noise reduction on the machine already. Do not use a DBX noise reduction system on HiFi stereo which already uses it. (almost all machines)

Reliability wise, for long term archival, I would choose Phongraph Record, 1/4 inch open reel, and F1 format. For searching and instant playback, the Hard Disk Drive beats the card catalog. Metadata is the key. However, hard disk is fragile and subject to corruption. Ordinary cassette tape without dolby has also shown to be pretty reliable.

By Sony's original format, I was referring to F1 format, compatible with units like the PCM1600, PCM-1 (1977) F1, PCM501, 601, 701 units. The convertors are obsolete or in need of modification, but the digital transport is 16 bit 44.1. This works with almost any NTSC video format except for lossy digital video. Thus, you can convert DAT to 8MM videotape, VHS, Betacam, Betamax, or any format. Because of HD TV, there's a glut of NTSC decks.

Sticky Shed:

Although the general rule is to do no harm, playing back a sticky shed tape, especially with the wax/crayon syndrome can actually do more damage than good. Heating the tape using the lightbulb method can sometimes "heal" the scratches and surface distortion with attempted playback.

DAT tapes prior to 1990:

There are some instances of sticky shed video and DAT tapes, mainly from 1988.

However, the problems you are having with old DAT tapes made prior to 1990 has to do with one of two issues:

1. DAT recorders from 1982 to 1989 used a slightly different Azmuth then those from 1990 to present. To play back these tapes, it is necessary to adjust the height of one of the tape guides on the playback machine to obtain the lowest error rate. To align a dat, use a tape recorded with a 22050 tone at full scale in phase with the sample rate (computer generated) and then adjust for lowest jitter. (24000 for 48 khz sample rates)

Second, many DAT tapes in the 80's were only recorded in 48 khz. Not all computer drives support 48 khz playback.

Mar. 31 2011 10:45 AM
Neil Schubert from USA

Another note.

One thing I'd like to suggest is that with material that has a significant level of sound quality, that it might be a good idea to make a copy using another modern more reliable tape, like ATR magnetics or Maxell. I've had pretty good luck with modern Ampex and Quantegy 641, though it requires a lower bias setting.

A pro VHS VCR makes a great backup device as well. Put 44.1 on the video, analog in DBX on the HiFi channels, and two channel cassette quality linear stereo on the tape as a backup. (verify that the deck has a stereo linear head)

Radio programming that was recorded off air generally stays in the realm of 44.1 recording. But classical, jazz and even pop recordings are more likely to be listened to, and it is really a good idea to make another reel if the original is degrading.

The hard disk drive and LTO tape are not invincible. What's an ESDI drive??? How do I read audio files from an ESDI drive in 2011? How about IDE in the year 2043?

The most reliable way to store a sound recording for a long period of time is a 33 1/3 RPM vinyl or hard plastic record. 100+ years.

Mar. 22 2011 01:58 PM
Neil Schubert from USA

Sticky and "Crayon" tape.

The process I use to restore sticky or crayon syndrome Ampex tape involves using a hot light bulb or vacuum tube to re-cure the tape as it is being played. The bulb heats the back side of the tape as it is being played. The center vent on an Otari MX5050 makes a great spot to install a tube, and one must use a variable control for the filament. A higher temp is used for backcoated tape. Unlike a tape oven, the tape is heated very evenly. One must babysit the recorder to make sure it doesn't get stuck. You must warm the tape in a tape oven FIRST before you allow it to unspool. Once it's warmed up, you can lightbulb it. The heated back blackcoat will usually fall off of the back of the tape like charcoal, but much will remain to perform its normal function. Once heated, the surface of the tape becomes hard again enough to play back a few times. I've had good success with it even years after, though it sometimes needs to be repeated. If you get the heat right, you can make your copy all as a one step process, playing and curing all at the same time. 3 3/4 or 7 1/2 is sometimes necessary to allow the tape to heat properly, and so half sample rates, etc may need to be used.

I am putting this up publicly for "for the good of all archivists and engineers". The reason we used a tape was because it was supposed to last a long time. Bad tape affects the entire music and radio industry, and puts US all out of work.

I've not had too many problems with Acetate. Usually, it gets brittle when it was either over or under tensioned and stored in a bad environment. My solution for badly cracking Acetate tape has been to bond it to plastic leader tape. If it is stuck together on a reel, it needs to be heated and or treated to separate it.

My worse nightmare has been early 80's brown non-backcoated Ampex that has separated. I once threaded a reel up, pressed play and luckily caught it before it got to the program.

The plastic portion of the tape went around the tape guide, but the oxide went straight. Never seen tape shed so perfectly.

As a general rule, I now warm to 110 degrees before unspooling, then go through the process of lightbulbing it. It must be unspooled in playback on a low tension machine, like a Fostex E-22 or a Teac Tascam 35-2, the second being what I prefer.

The best analog tape is 1960's and 1950's era Scotch, like 109 or 111. In digital, Sony's original video format blows away DAT.

Mar. 22 2011 10:08 AM
Neil Schubert from USA

Some Help for Everyone

So far, my conclusion is that the backcoating is not necessarily the cause of sticky shed, but a contributing factor. The backcoat on sticky shed Ampex is not carbon, but underheated (improperly cured) rubber or synthetic rubber. It is basically a mixture (not a compound) of the same stuff they used to make those tarry belts you pull off of reel to reel recorders and phonograph drives, and some tape machine pinch rollers. Backcoat is your friend, though sometimes it may seem like your worse enemy.

Which do you want to deal with?

A. An over-tensioned tape with no backcoating in which the oxide of the tape sticks to the next layer in the reel.

B. A tape with backcoating that sticks to the playing surface and causes dropouts, deposits, and squeaking / sticking?

With the backcoat, all you need to do to separate the tape is to warm it up. The heat usually rebonds the oxide to the plastic portion of the tape, and the sticky rubber surface unglues itself from the oxide portion. If the oxide doesn't have "crayon" syndrome, you need to take the time to clean the tape and get the backcoat off of the playing surface. Mr. Richardson has a great idea in making a mechanism to remove the backcoat from the oxide. However, one must be cautious when touching the play surface of the tape so as to not pick up oxide and add noise to the tape as well as potentially wearing off "crayon" syndrome tapes.

Without the backcoat, the problem is that an over-tensioned tape can potentially have oxide that sticks to both sides. I've even had Maxell do this! Warming the tape up on the reel can many times resolve the issue. You can't expect that everybody does a full loose rewind through the tape prior to shelving it. We'd like to think so, but that's just not reality!

So far, the sticky shed syndrome only applies to tape manufactured or contracted by Ampex. Some of the best recorders were made by Ampex. And some of the worst tape!!!

Backcoated Scotch 207 (and its different thicknesses like 211), Maxell, and FujiFilm tapes do not seem to have sticky backcoat. The binder sometimes causes flaking on 207, but this is usually due to stretching or scraping on a recorder with friction points. 3M's backcoat is not made of rubber. They did have problems with the "classic" series in 1984 and 85.

Mar. 22 2011 10:06 AM

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