mould

Videokunstarkivet’s Mouldy U-matic Video Tapes

Lives and VideotapesLast year we featured the pioneering Norwegian Videokunstarkivet (Video Art Archive) on the Greatbear tape blog.

In one of our most popular posts, we discussed how Videokunstarkivet has created a state of the video art archive using open source software to preserve, manage and disseminate Norway’s video art histories for contemporary audiences and beyond.

In Lives and Videotapes, the beautiful collection of artist’s oral histories collected as part of the Videokunstarkivet project, the history of Norwegian video art is framed as ‘inconsistent’.

This is because, Mike Sperlinger eloquently writes, ‘in such a history, you have navigate by the gaps and contradictions and make these silences themselves eloquent. Videotapes themselves are like lives in that regard, the product of gaps and dropout—the shedding not only of their material substance, but of the cultural categories which originally sustained them’ (8).

The question of shedding, and how best to preserve the integrity of audiovisual archive object is of course a vexed one that we have discussed at length on this blog.

It is certainly an issue for the last collection of tapes that we received from Videokunstarkivet—a number of very mouldy U-matic tapes.

umatic-dry-mould-inside-cassette-shellAccording to the Preservation Self-Assessment Program website, ‘due to media and hardware obsolescence’ U-matic ‘should be considered at high preservation risk.’

At Greatbear we have stockpiled quite a few different U-matic machines which reacted differently to the Videokunstarkivet tapes.

As you can see from the photo, they were in a pretty bad way.

 Note the white, dusty-flaky quality of the mould in the images. This is what tape mould looks like after it has been rendered inactive, or ‘driven into dormancy.’ If mould is active it will be wet, smudging if it is touched. In this state it poses the greatest risk of infection, and items need to be immediately isolated from other items in the collection.

Once the mould has become dormant it is fairly easy to get the mould off the tape using brushes, vacuums with HEPA filters and cleaning solutions. We also used a machine specifically for the cleaning process, which was cleaned thoroughly afterwards to kill off any lingering mould.

The video tape being played back on vo9800 U-matic

This extract  demonstrates how the VO9800 replayed the whole tape yet the quality wasn’t perfect. The tell-tale signs of mould infestation are present in the transferred signal.

Visual imperfections, which begin as tracking lines and escalate into a fuzzy black out of the image, is evidence of how mould has extended across the surface of the tape, preventing a clear reading of the recorded information.

Despite this range of problems, the V09800 replayed the whole tape in one go with no head clogs.

SONY BVU 950

The video tape being played back on SONY BVU 950

In its day, the BVU950 was a much higher specced U-matic machine than the VO9800. As the video extract demonstrates, it replayed some of the tape without the artefacts produced by the V09800 transfer, probably due to the deeper head tip penetration.

Yet this deeper head penetration also meant extreme tape head clogs on the sections that were affected badly by mould—even after extensive cleaning.

This, in turn, took a significant amount of time to remove the shedded material from the machine before the transfer could continue.

Mould problems

The play back of the tapes certainly underscores how deeply damaging damp conditions are for magnetic tape collections, particularly when they lead to endemic mould growth.

Yet the quality of the playback we managed to achieve also underlines how a signal can be retrieved, even from the most mould-mangled analogue tapes. The same cannot be said of digital video and audio, which of course is subject to catastrophic signal loss under similar conditions.

As Mike Sperlinger writes above, the shedding and drop outs are important artefacts in themselves. They mark the life-history of magnetic tapes, objects which so-often exist at the apex of neglect and recovery.

The question we may ask is: which transfer is better and more authentic? Yet this question is maddeningly difficult to answer in an analogue world defined by the continuous variation of the played back signal. And this variation is certainly amplified within the context of archival transfers when damage to tape has become accelerated, if not beyond repair.

At Greatbear we are in the good position of having a number of machines which enables us to test and experiment different approaches.

One thing is clear: for challenging collections, such as these items from the Videokunstarkivet, there is no one-size-fits-all answer to achieve the optimal transfer.

Posted by debra in Audio / Video Archives, Video Tape, 0 comments

Mouldy DATs

We have previously written on this blog about the problems that can occur when transferring Digital Audio Tapes (DATs).

According to preliminary findings from the British Library’s important survey of the UK’s sound collections, there are 3353 DAT tapes in the UK’s archives.

While this is by no means a final figure (and does not include the holdings of record companies and DATheads), it does suggest there is a significant amount of audio recorded on this obsolete format which, under certain conditions, is subject to catastrophic signal loss.

The conditions we are referring to is that old foe of magnetic tape: mould.

In contrast with existing research about threats to DAT, which emphasise how the format is threatened by ‘known playback problems that are typically related to mechanical alignment’, the biggest challenges we consistently face with DATs is connected to mould.

It is certainly acknowledged that ‘environmental conditions, especially heat, dust, and humidity, may also affect cassettes.’

Nevertheless, the specific ways mould growth compromise the very possibility of successfully playing back a DAT tape have not yet been fully explored. This in turn shapes the kinds of preservation advice offered about the format.

What follows is an attempt to outline the problem of mould growth on DATs which, even in minimal form, can pretty much guarantee the loss of several seconds of recording.

DAT Tape SizeTape width issues

The first problem with DATs is that they are 4mm wide, and very thin in comparison to other forms of magnetic tape.

The size of the tape is compounded by the helical method used in the format, which records the signal as a diagonal stripe across the tape. Because tracks are written onto the tape at an angle, if the tape splits it is not a neat split that can be easily spliced together.

The only way to deal with splits is to wind the tape back on to the tape transport or use leader tape to stick the tape back together at the breaking point.

Either way, you are guaranteed to lose a section of the tape because the helical scan has imprinted the recorded signal at a sharp, diagonal angle. If a DAT tape splits, in other words, it cuts through the diagonal signal, and because it is digital rather than analogue audio, this results in irreversible signal loss.

And why does the tape split? Because of the mould!

If you play back a DAT displaying signs of dormant mould-growth it is pretty much guaranteed to split in a horrible way. The tape therefore needs to be disassembled and wound by hand. This means you can spend a lot of time restoring DATs to a playable condition.

Rewinding by hand is however not 100% fool-proof, and this really highlights the challenges of working with mouldy DAT tape.

Often mould on DATs is visible on the edge of the tape pack because the tape has been so tightly wound it doesn’t spread to the full tape surface.

In most cases with magnetic tape, mould on the edge is good news because it means it has not spread and infected the whole of the tape. Not so with DAT.

Even with tiny bits of mould on the edge of the tape there is enough to stick it to the next bit of tape as it is rewound.

When greater tension is applied in an attempt to release the mould, due to stickiness, the tape rips.

A possible and plausible explanation for DAT tape ripping is that due to the width and thinness of the tape the mould is structurally stronger than the tape itself, making it easier for the mould growth to stick together.

When tape is thicker, for example with a 1/4 ” open reel tape, it is easier to brush off the dormant mould which is why we don’t see the ripping problem with all kinds of tape.

Our experience confirms that brushing off dormant mould is not always possible with DATs which, despite best efforts, can literally peel apart because of sticky mould.

What, then, is to be done to ensure that the 3353 (and counting) DAT tapes in existence remain in a playable condition?

One tangible form of action is to check that your DATs are stored at the appropriate temperature (40–54°F [4.5–12°C]) so that no mould growth develops on the tape pack.

The other thing to do is simple: get your DAT recordings reformatted as soon as possible.

While we want to highlight the often overlooked issue of mould growth on DATs, the problems with machine obsolescence, a lack of tape head hours and mechanical alignment problems remain very real threats to successful transfer of this format.

Our aim at the Greatbear is to continue our research in the area of DAT mould growth and publish it as we learn more.

As ever, we’d love to hear about your experiences of transferring mouldy DATs, so please leave a comment below if you have a story to share.

 

Posted by debra in Audio Tape, 0 comments

Transferring Digital Audio Tapes (DATs) to digital audio files

This post focuses on the problems that can arise with the transfer of Digital Audio Tapes (DATs).

An immature recording method (digital) on a mature recording format (magnetic tape), the audio digital recording revolution was never going to get it right first time (although DATs were not of course the first digital recordings made on tape).

Indeed, at a meeting of audio archivists held in 1995, there was a consensus even then that DAT was not, and would never be, a reliable archival medium. One participant stated: ‘we have tapes from 1949 that sound wonderful,’ and ‘we have tapes from 1989 that are shot to hell.’ And that was nearly twenty years ago! What chances do the tapes have now?

A little DAT history

Before we explore that, let’s have a little DAT history.

SONY introduced Digital Audio Tapes (DATs) in 1987. At roughly half the size of an analogue cassette tape, DAT has the ability to record at higher, equal or lower sampling rates than a CD (48, 44.1 or 32 kHz sampling rate respectively) at 16 bit quantization.

Although popular in Japan, DATs were never widely adopted by the majority of consumer market because they were more expensive than their analogue counterparts. They were however embraced in professional recording contexts, and in particular for recording live sound.

It was recording industry paranoia, particularly in the US, that really sealed the fate of the format. With its threatening promise of perfect replication, DAT tapes were subject to an unsuccessful lobbying campaign by the Recording Industry Association of America (RIAA). RIAA saw DATs as the ultimate attack on copyright law and pressed to introduce the Digital Audio Recorder Copycode Act of 1987.

This law recommended that each DAT machine had a ‘copycode’ chip installed that could detect whether prerecorded copyrighted music was being replicated. The method employed a notch filter that would subtly distort the quality of the copied recording, thus sabotaging acts of piracy tacitly enabled by the DAT medium. The law was however not passed, and compromises were made, although the US Audio Home Recording Act of 1992 imposed taxes on DAT machines and blank media.

How did they do ‘dat?

Like video tape recorders, DAT tapes use a rotating head and helical scan method to record data. The helical scan can, however, pose real problems for the preservation transfers of DAT tapes because it makes it difficult to splice the tape together if it becomes sticky and snaps during the tape wind. With analogue audiotape, which records information longitudinally, it is far more possible to splice the tape together and continue the transfer without risking irrevocable information loss.

Another problem posed by the helical scan method is that such tapes are more vulnerable to tape pack and backing deformation, as the CLIR guide explain:

‘Tracks are recorded diagonally on a helical scan tape at small scan angles. When the dimensions of the backing change disproportionately, the track angle will change for a helical scan recording. The scan angle for the record/playback head is fixed. If the angle that the recorded tracks make to the edge of the tape do not correspond with the scan angle of the head, mistracking and information loss can occur.’

When error correction can’t correct anymore

dat-mute-playback-condition-sony-7040Most people will be familiar with the sound of digital audio dropouts even if they don’t know the science behind them. You will know them most probably as those horrible clicking noises produced when the error correction technology on CDs stops working. The clicks indicate that the ‘threshold of intelligibility’ for digital data has been breached and, as theorist Jonathan Sterne reminds us, ‘once their decay becomes palpable, the file is rendered entirely unreadable.’

Our SONY PCM 7030 professional DAT machine, pictured opposite, has a ‘playback condition’ light that flashes if an error is present. On sections of the tape where quality is really bad the ‘mute’ light can flash to indicate that the error correction technology can’t fix the problem. In such cases drop outs are very audible. Most DAT machines did not have such a facility however, and you only knew there was a problem when you heard the glitchy-clickety-crackle during playback when, of course, it was too late do anything about it.

The bad news for people with large, yet to be migrated DAT archives is that the format is ‘particularly susceptible to dropout. Digital audio dropout is caused by a non-uniform magnetic surface, or a malfunctioning tape deck. However, because the magnetically recorded information is in binary code, it results in a momentary loss of data and can produce a loud transient click or worse, muted audio, if the error correction scheme in the playback equipment cannot correct the error,’ the wonderfully informative A/V Artifact Atlas explains.

Given the high density nature of digital recordings on narrow magnetic tape, even the smallest speck of dust can cause digital audio dropouts. Such errors can be very difficult to eliminate. Cleaning playback heads and re-transferring is an option, but if the dropout was recorded at the source or the surface of tape is damaged, then the only way to treat irregularities is through applying audio restoration technologies, which may present a problem if you are concerned with maintaining the authenticity of the original recording.

Listen to this example of what a faulty DAT sounds like

Play back problems and mouldy DATs

Mould growth on the surface of DAT tape

Mould growth on the surface of DAT tape

A big problem with DAT transfers is actually being able to play back the tapes, or what is known in the business as ‘DAT compatibility.’ In an ideal world, to get the most perfect transfer you would play back a tape on the same machine that it was originally recorded on. The chances of doing this are of course pretty slim. While you can play your average audio cassette tape on pretty much any tape machine, the same cannot be said for DAT tapes. Often recordings were made on misaligned machines. The only solution for playback is, Richard Hess suggests, to mis-adjust a working machine to match the alignment of the recording on the tape.

As with any archival collection, if it is not stored in appropriate conditions then mould growth can develop. As mentioned above, DAT tapes are roughly half the size of the common audiocassette and the tape is thin and narrow. This makes them difficult to clean because they are mechanically fragile. Adapting a machine specifically for the purposes of cleaning, as we have done with our Studer machine, would be the most ideal solution. There is, however, not a massive amount of research and information about restoring mouldy DATs available online even though we are seeing more and more DAT tapes exhibiting this problem.

As with much of the work we do, the recommendation is to migrate your collections to digital files as soon as possible. But often it is a matter of priorities and budgets. From a technical point of view, DATs are a particularly vulnerable format. Machine obsolescence means that compared to their analogue counterparts, professional DAT machines will be increasingly hard to service in the long term. As detailed above, glitchy dropouts are almost inevitable given the sensitivity and all or nothing quality of digital data recorded on magnetic tape.

It seems fair to say that despite being meant to supersede analogue formats, DATs are far more likely to drop out of recorded sound history in a clinical and abrupt manner.

They therefore should be a high priority when decisions are made about which formats in your collection should be migrated to digital files immediately, over and above those that can wait just a little bit longer.

Posted by debra in Audio Tape, 0 comments