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The Great Tape Bake Off

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Sticky tapes

One of the many challenges we face when digitising audiovisual material from magnetic tape is “sticky-shed syndrome”. Certain types or formulations of tape suffer from this problem that, as the name implies, causes them to literally stick to the components of the playback machine creating a phenomenon known as “stiction”. The friction of the sticky tape against the metal parts causes screeching/squealing noises and slowed/ uneven speed of tape playback. Sometimes the machine will slow down and grind to a halt. If you haven’t encountered this phenomenon before you could be forgiven for thinking it’s a fault on the player. Playback of sticky tapes can result in damage to the tape and in some cases, the playback equipment. The magnetic oxide material sheds from the tape resulting in a distorted signal and dropouts which compromise the quality of the digital transfer. Extreme sticky-shed can cause catastrophic damage to a tape and result in partial or complete loss of the often unique audiovisual material contained on that tape.

A magnetic tape which has been so affected by shedding that the oxide which holds the magnetic information (brown), has completely come away from the polyester base (clear) rendering the information unrecoverable. Picture by Anothermelbournite, Wikipedia

Ingredients

Magnetic tape consists of a plastic base layer (substrate), a layer of magnetic oxide or metal particle material (the brown stuff that contains the audiovisual signal) with lubricants and a binder which glues the oxide/metal particles to the base. Some tapes contain an additional back-coat on the base designed to lubricate the motion of the tape through the player and reduce friction.

Structure of magnetic tape, picture from https://publish.uwo.ca/~dspanner/LIS9670/lect11.htm

The problem of sticky-shed results from a breakdown in the binder resulting in hydrolysis i.e. absorption of water. The urethane molecules in the polyurethane binder react with the water, making them migrate to the surface of the tape where they cause the stickiness.

The issue is difficult to identify by visual inspection but suspect tapes should be tested before attempting playback by slowly turning the reel and observing whether the tape unspools naturally or sticks/lingers on the pack. Sometimes the tape surface can exhibit a soft/gummy quality. The problem of sticky tapes has become more apparent over the last 30 years as tape stock ages and patterns of binder breakdown have been identified. Certain brands manufactured entire batches of tape with a faulty binder formulation which almost invariably suffer from sticky-shed. This makes it easier to identify a tape that will have problematic playback before placing it in/on the machine.

Recipe

Thankfully, for most cases of sticky-shed there is a solution – “Baking” the tapes i.e. heating them gently for a period of a few hours. For this purpose, I use a food dehydrator as it is suitable for lower heating temperatures and maintaining them more consistently than a conventional oven. My ultimate goal is to obtain an incubator which operates at the most consistent temperatures over long periods but for now, the dehydrator does the job well. Any apparatus used should not contain strong magnetic fields which can damage the tape’s content. A digital thermometer allows easy and accurate temperature monitoring.

Food dehydrator used for “baking” tapes with sticky-shed syndrome

Baking at 54.4°C (130°F) is the sweet spot to temporarily reverse sticky-shed syndrome. The duration required varies for each format but should be at least 2-3 hours with tapes flipped once or twice then allowed to cool for at least the same length of time. Once baked, there is a short window of a few days to digitise before hydrolysis makes the tape sticky again. It’s wise to carry out the process during drier weather conditions as humidity in the air will speed up hydrolysis. A tape can however, be re-baked several times and this is often a requirement for some of the more stubborn formats anyway. As there isn’t 100% consistency of tape behaviour, it can be a case of trial and error – bake for the minimum time, manually test unspooling of tape and carefully attempt playback. If not successful, bake again and so on until the tape plays back correctly.

The main tapes to look out for are:

• Reel to reel audio tapes – Ampex/Quantegy (mid 1970s into the early 1990s) and Scotch/3M. Bake for 3-6 hours.

Ampex 1/4″ audio tape reel

• U-matic video tapes (1975-1985) by Ampex, AGFA and Sony – those affected often have a wax crayon type smell. The tape reels should be removed from the cassette shell for baking. Bake for 8-16 hours.

Sony U-matic video cassette

• EIAJ ½” open reel video tape – particularly Sony branded V60H, V62 and V30H Helical Scan. If the tape is back coated, it will require baking. These tapes often require long bake times, I have found that manually winding and cleaning with a lint-free cloth after baking can improve playback results. Bake for 8-16 hours, sometimes multiple bakes are required.

Sony 1/2″ video tape reels

• Quad 2” open reel video tape. We don’t currently have any of these in our archives but due to their large size they require extended baking times – up to 24 hours.

Other formats can occasionally suffer from sticky-shed too e.g. Betacam (oxide formulation), VHS, Hi8, even MiniDV.

If you are in doubt as to whether a given tape has sticky-shed syndrome it is much safer to bake it than play it.

Audio compact cassettes are an exception in that the faulty binder was not used in cassette formulations. However, some cassettes can suffer from stickiness due to fatty acids migrating to the surface of the tape. I have baked some notoriously sticky mid-1980s EMI cassettes for 2-4 hours with excellent results.

Slow cassette:

Baked cassette:

The Raw and the Cooked

Just to confuse things, some tapes can also suffer from a different type of Soft Binder Syndrome which can cause squealing on playback. These are often non back-coated tapes and leave less of a deposit on the playback path. It is not recommended to bake these as it can exacerbate the problem. Some success has been achieved by playing back this kind of tape in a cold environment, even placing a playback machine inside a refrigerator. Other tapes display a problem where the back-coat of the tape is turning to powder leaving a non-sticky accumulation of powder on the playback heads. These also shouldn’t be baked but cleaning will be necessary. Finally, never bake an acetate tape. These can be identified when held up to a bright light and visible light can be seen coming through the tape pack.

Despite these exceptions, the most common type of tape degradation you are ever likely to come across is sticky-shed syndrome.

It’s always worth that extra effort to ensure our AV material is preserved in its optimum form.
Happy Baking!

Nigel Bryant
Audiovisual Digitisation Officer

 

Critical Analysis of Oral History Practice Interviews

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Following Jan Wozniak’s  blog post in September 2024, students on this research unit have contributed a series of blogs on their experiences of learning about and creating oral histories.

 

Critical Analysis of Interview by Jan Wozniak with Lucy Hunt, Director of Engagement at Bristol Old Vic

By Unit students Naama, Nell and Lola

This blog recognises that most of these critical observations arose from the specific circumstances of classroom-based practice interviews and are unlikely to occur in typical oral history interviews.

The interview took place in our usual seminar room, a relatively large space that accommodates around 30 people. Under different circumstances, a smaller, more intimate setting would have been preferable for recording. Upon reviewing the recording, I noticed significant background noise, particularly the sound of passing police cars. Ideally, interviews should be conducted in a smaller, acoustically soft room without an audience, to minimise external sounds and distractions. The presence of laughter in the recording, for instance, may have influenced the interviewee’s responses or reactions. Furthermore, the recording was done on a basic camcorder without specialised audio equipment, which impacted the audio quality significantly. In retrospect, using microphones and high-quality recording devices would have enhanced clarity and reduced ambient noise interference.

Jan made a conscious effort to maintain strong eye contact with Lucy, which helped her feel engaged and listened to. He avoided crossing his arms – while a natural and comfortable position for many, it can sometimes convey a sense of closed-off body language. As an interviewer, it is important to remain mindful of one’s body language and how it might be perceived by the interviewee, as their perception can influence the openness of their reponses.

As the interview progressed, Jan noticed that Lucy appeared confident and secure in her responses, which allowed him to introduce more challenging questions. For example, when Lucy explained that the Young Company was divided by age groups, Jan questioned this and asked why the young people were separated into year groups as at school, when the goal is to distinguish this environment from traditional schooling. Lucy responded comfortably, demonstrating that she felt respected and that Jan’s questions were a product of active listening and critical engagement.

Finally, I observed that Jan began taking notes during the interview. This was likely a practical strategy to aid in post-interview debriefing, yet, as we are reflecting critically, it raised a potential issue. Note-taking during an interview could potentially affect the intervewee’s comfort, as they may become self-conscious about what is being noted versus what is not, leading them to question the perceived significance of their statements. This highlights the importance of considering how the interviewer’s actions may subtly influence the interviewee’s mindset and responses. As noted earlier, while the interviewer is actively perceiving and analysing the interviewee, the reverse is also true: the interviewee is reading and responding to the interviewer’s cues.

Personal Reflection of Student Interview with Lisa Gregan, Director of the Bristol Old Vic Young Company

After Jan completed the interview with Lucy, he opened up the next interview with Lisa Gregan to the rest of the class. I nervously raised my hand, thinking someone else would too. They didn’t of course, so 10 minutes later there I was with Lisa, conducting an interview. Scary stuff!

It helped that Jan had gone first; I was able to take inspiration from his style and questions, as I had none prepared. I tried to maintain open body language, show active listening through eye contact and verbal recognition, and asked follow-up questions where it seemed right.

I realised as I sat there panicking about what to ask next, that it didn’t actually matter. The point was never to be the most interesting interviewer, rather to help and facilitate the most interesting interviewee! This change in my understanding allowed me to relax and truly, deeply listen to Lisa, which resulted in far better questions and a more comfortable environment for Lisa.

World Digital Preservation Day: Reflecting on a Year of Digital Archiving

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Lori Stirland-Legret, Digital Archive Assistant, reflects on the last year of digital activities in Special Collections and Theatre Collection for this year’s World Digital Preservation Day.

Today is the first Thursday of November, meaning it’s World Digital Preservation Day 2024! This is a day to celebrate all things relating to digital preservation, and this year’s theme is ‘Preserving Our Digital Content: Celebrating Communities’. It has also been almost exactly a year since I started working as Digital Archive Assistant for Special Collections and Theatre Collection, so it seemed like a good time to reflect on the work I’ve been doing, as well as the importance of digitally preserving our collections.

One of the main tasks that I’ve undertaken is creating a Digital Asset Register to keep information about all of our digital collections in one place. It contains high level information such as how much storage space each collection takes up, and the types of digital files they contain. With a Digital Asset Register, we can get a better idea of which collections to prioritise to make accessible for users.

Making a Digital Asset Register sounds easy until you consider that Special Collections has over 40 terabytes and Theatre Collection has over 50 terabytes of digital content. To put it into perspective, the average laptop usually has a capacity of around 500 gigabytes of storage – meaning it would take almost 200 normal laptops to hold all of our digital materials! Luckily, we have access to a large amount of network storage as well as Preservica, our digital asset management system.

I’ve also been able to do a lot of work on creating online exhibitions for Special Collections and Theatre Collection. Most recently, in October the Cultural Collections Black History Month online exhibition went live. Working on these has given me a lot of perspective on the amount of work from everyone that goes into making collections accessible: from selecting suitable materials, digitising copies, and doing all the technical coding. However, it feels very satisfying to finally create a finished product which anyone can access from their mobile phone in the palm of their hand! It’s currently still online, so be sure to check it out if you haven’t already.

Cultural Collections’ Black History Month online exhibition. Image shows playwright Winsome Pinnock (left) with director Hettie McDonald. Theatre Collection (ref WPT/1/1/2/2/9/1)

Looking forward, over the next year one of our main goals is to get more content into Preservica and accessible to users, ensuring our digital collections are as protected and accessible as possible. In the same way that you can put a book at the back of a pile and then forget about it, digital files can be hidden away in folders on old computers only to be lost. Physical archives are vulnerable to a number of real-life disasters, and whilst digital archives have their own vulnerabilities, taking a multifaceted approach gives our records the best chance of surviving for as long as possible.

Performing the Constitution: 19th Century Productions of Shakespeare’s King John, by Ruth Houghton (Newcastle Law School)

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Researcher Ruth Houghton visited the Theatre Collection in 2023 to examine the Herbert Beerbohm Tree Business Archive. This blog highlights her reading room discoveries around Tree’s 1899-1900 production of King John, which have led to her 2024 article, published in the journal Law and Humanities (full details below).

 

King John is probably best known for sealing Magna Carta in 1215. Yet, this significant event in the constitutional history of Great Britain does not feature in Shakespeare’s play The Life and Death of King John; a fact that has preoccupied both literary and historical scholars. In contrast, 19th century productions of the play were littered with references to the Charter. From discussions in the programmes of the events at Runnymede to insertions into the very text of the play about the rights and liberties protected by Magna Carta, theatre producers across the century were reimagining the role of the Charter within the play.

No-one does this more spectacularly than Herbert Beerbohm Tree. In his 1899 production of King John at Her Majesty’s Theatre in London (which incidentally would go on to be the first filmed recording of a Shakespeare production), Beerbohm Tree staged a magnificent tableau – or living picture – depicting ‘The Granting of Magna Charta’.

HBT/40/1 Souvenir programme for King John at Her Majesty’s Theatre, 20 September 1899.

The tableau is often assumed to be silent, a ‘dumb-show’, which scholars have argued facilitated an a-political representation of Magna Carta as it allowed Beerbohm Tree to display the historical moment of the sealing of the Charter without praise or blame. (source: J. M. Lander and J. J. M. Tobin (eds) The Arden Shakespeare: King John (3rd edn, Bloomsbury 2018), p.102.)

However, documents in the Herbert Beerbohm Tree Business Archive give insight into the specific sounds and movements that accompanied the scene.

In the Stage [rehearsal] Notes of the tableau from the 13th September 1899, it states:

‘Super is holding document, puts it on table in front of JOHN, points to it for JOHN’S signature. After John has put his hand to the seal – inspiring music – then shout from everyone onstage.’

HBT/40/44 Stage Notes for King John at Her Majesty’s Theatre 1899-1900.

However, the Property Plot (undated but presumably created separately on a different day), details minor alterations that give an alternative approach to the scene:

‘Document is on table – Mr Tree [as King John] enters, goes towards table, man takes up document, gives it to Mr Tree, who reads it, looks round at Nobles, puts down the document, looks around again, then puts finger on paper – Music changes to ‘joyous rainbow’ strain – Mr Tree gives paper back to man – Loud cheers.’

HBT/40/13 Property Plot for King John at Her Majesty’s Theatre, 1899-1900.

The archive here uncovers a more complicated representation of the constitutional significance of the Charter. On 13th September, the pointing for a signature could be constructed as a visual representation of John being asked to submit, reluctantly, to the demand of the barons. In contrast, the longer stage direction of HBT/40/13 has the additional ‘gives paper back’, which is evocative of the idea that John gives the charter (almost magnanimously) to the people. Indeed, the ‘cheers’ in this rehearsal happen when the people are in possession of the Charter.

These two versions of the tableau found in the archives present distinct constitutional readings. Whilst one exaggerates the symbolism of the Charter as an act of holding a sovereign to account, the other places emphasis on the idea that the people now possess rights and liberties. These notes therefore offer a fascinating insight into how representations of Magna Carta in 19th century productions of King John can shed light on the perception and development of the Charter’s constitutional status during this period.

The Herbert Beerbohm Tree Business Archive is housed in the University of Bristol Theatre Collection.

This research has been published in Houghton, R. (2024). ‘Performing a constitution: a history of Magna Carta in Shakespeare’s King John’. Law and Humanities, 1–30. https://doi.org/10.1080/17521483.2024.2370673.

 

The challenges (and rewards!) of preserving video from MiniDV tapes

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DV or digital video tape is a format that was launched in 1995 and remained popular until the late 2000s. There are a few varieties of this type of tape but I want to discuss the consumer format known as MiniDV.

Video cassette and Mini DVD cassette
1 – VHS cassette and Mini DV cassette

DV technology brought a considerable jump in quality from previous camcorder formats such as VHS and Hi8 with more compact and relatively affordable equipment. This made MiniDV a popular choice for arts organisations to document their work so we have a lot of these tapes in our more contemporary theatre and live art collections.

During 2023/24 I worked on the preservation of the audiovisual material in the Rideout collection which includes around 150 MiniDV tapes. Rideout, subtitled Creative Arts for Rehabilitation was established in 1999 by Saul Hewish and Chris Johnston to develop innovative, arts-based approaches to working with prisoners and staff within UK prisons.

The condition of the tapes indicated that they had been stored fairly well with no signs of physical damage or mould which can often be a problem when tapes are stored in conditions with varying temperature and relative humidity.

The process of preserving the audiovisual material on DV tapes involves copying the digital information encoded on the tape to a digital file on a computer. This differs from the process for analogue tape such as VHS which requires a digitisation process i.e. analogue to digital conversion. Copying the data from tape gives the optimal audiovisual quality and also has the benefit of retaining metadata such as the time/date of the recording, camera settings used, and error information. The tape must be played back in a suitable DV playback machine aka “deck” or camcorder in real time and the digital information on the tape can be copied directly to a computer using a Firewire cable connection or IEEE 1394 to give its correct technical name.

electrical cable
2 – Firewire (IEEE 1394) cable

The first challenge is that Firewire technology is obsolete. It used to be a fairly standard interface, especially in Macintosh computers but now you need to install a Firewire card to your computer or use some kind of converter cable. We use the first option.

The second challenge is that playback decks or camcorders for DV tapes are no longer manufactured so second-hand units must be purchased. The price for professional decks is rising as the demand for preserving DV based material increases. We currently have four pro decks which all need occasional servicing to keep them running properly. Engineers familiar with this type of equipment are also getting harder to find.

piece of equipment for digital videocasette recording
3 – Sony DSR-1500P DVCAM deck

So we have our deck, firewire cable and computer – this is the basic equipment needed to copy DV tapes. I also use a video monitor, amplifier and speakers to monitor the off-tape signal directly during playback.

Another challenge I discovered with this particular collection of tapes was that a fair proportion of them had been recorded in long play (LP) mode. None of my four professional DV decks are long play compatible so it is not possible to make a good quality digital copy of those tapes with them. There are a couple of professional decks that will play long play tapes but they are extremely hard to find and are accordingly very expensive. The solution was straight forward – most Mini DV camcorders will play Long Play tapes back well and are still an affordable option (£100 or less on eBay).

One of our main challenges with the tapes themselves is that they are prone to errors caused by signal dropout of video and audio from dirty or damaged tape. DV uses a technique called error concealment to try to disguise this dropout – this can include replacing the affected area with the same corresponding pixels of the previous frame or next frame (most common). Sometimes this strategy works so well that it is not noticeable in the resulting file, especially with static frame shots that contain a high degree of visual similarity from one frame to the next. However, when there is lots of movement, error concealment can cause the image to appear glitchy or blocky.

image with errors blocking
4 – Error concealment causing blocking effect on person’s face

Audio errors can result in jarring clicks or loss of signal. Sometimes fast forwarding or rewinding a tape can remove errors, on other occasions manual cleaning of the video heads may be required. Even where the errors cannot be eliminated by these methods, tapes often don’t behave consistently when played back – they can display errors over certain sections and on subsequent plays fail to display the same errors or show errors in different sections of the tape. This behaviour can actually be used to our advantage in creating the best preservation copy possible which I will explain shortly.

In order to copy the information from the tapes to create our digital preservation files we need suitable software. Most Non-Linear Editing (NLE) software packages including Adobe’s popular Premiere Pro no longer support tape-based workflows. There are some older freeware options but these are no longer technically supported and can be unstable or unavailable for certain operating systems. Thankfully, the international community of video archivists and engineers has come to the rescue (literally) with a versatile free open-source solution called DVRescue. Open-Source means that end users and developers have the freedom to study, improve and redistribute the software.

screenshot of outdoor event with timecode and date
5 – Detail of DVRescue capture interface

DVrescue supports many of the commonly used professional DV playback decks and its capture interface displays timecodes, time & date of recording as well as a real-time graph of errors detected during the capture. Once your tape capture is completed the software has an analysis tool that pinpoints the position and nature of each error so that you can examine the effect on the video/audio in your file. Finally, there is the option to package the captured raw DV stream into a suitable file container – we use Matroska which is an open standard media container commonly used in video archives.

There are additional features in DVRescue that can be accessed via the command line, most useful of these for me is the merge function. This allows you to take two or more separate passes of the capture and combine them. The process takes advantage of the inconsistency of error display on subsequent plays, mentioned earlier, to return one file containing the best frames from each pass. By capturing short sections of video over known error regions and merging these with your master capture you can create the optimal preservation file.

command text
6 – DVRescue merge command

So far so good, we have a set-up that can optimise our DV captures and produce greatly improved results from previous workflows. However…remember those Long Play recordings I mentioned earlier? The ones we have to play back with a camcorder? Well the camcorder is not supported by DVRescue so we have to use an alternative capture software. I use a discontinued software called Scenalyzer for Windows, this doesn’t have any of the sophisticated error reporting or analysis tools present in DVRescue but it does allow us to capture the tape in AVI format and retain the recording’s metadata. The files can then be analysed using a standalone piece of open-source software called DVAnalyzer.  Errors can be identified and located and further corrective tape passes can be made. The resulting files must be converted to a raw DV stream before they can be merged with DVRescue to produce a best quality master copy. This conversion is done using an open-source command line tool – FFMpeg. We can then merge the files as before and re-package the master to a Matroska container.

So we have our workflow for producing preservation copies of these digital tapes. This is all great as long as your tapes are behaving but amongst any collection of DV tapes you will inevitably find problems.

  • Tapes that are dirty. Playback may be improved by cleaning – I do this by using one of my decks that I can open up to access the tape path, I then hold a special cleaning swab lightly against the tape and fast forward and rewind it. This isn’t always successful but has definitely improved the performance of some tapes.
  • Tapes causing “head clogs” – within seconds of playback the picture and sound will drop out due to particles shedding from the tape. The deck will not play back any tape until the heads have been manually cleaned. Cleaning and sometimes “baking” i.e. heating the tape to 54°C for a few hours) can improve performance. Where the head clogs are severe, tapes will have to be captured in sections with manual cleaning of the heads in between – a laborious and time-consuming process.
  • Damaged cassettes – the cassette shell may be damaged and prevent it from playing back or even being accepted by a deck. For these, the tape reels can be removed and transferred into a replacement cassette shell to achieve playback. Due to the size of the tapes this can be a fiddly process.

All that remains after our digital preservation copies have been produced is to create access or viewing copies for each file. These are smaller, more manageable files suitable for easy playback or sharing. I create these using a Non-Linear Editing (NLE) Software e.g. Premiere Pro or Shotcut which allows me to make adjustments for optimal viewing before creating the access copy file. All the digital files are then securely copied to and stored on the university’s Research Data Storage Facility.

I’m happy to report that I’ve managed to produce digital preservation copies of every DV tape in the Rideout collection. Some are perfect with no errors whatsoever, the majority have a few minor errors which may or may not be noticeable and just one has substantial errors throughout, although most of the contents of the tape can still be viewed and listened to. A fair bit of painstaking work was carried out to preserve the collection but I believe the additional effort required to get the optimal results is well worth it. Overcoming the challenge of obsolescent technology to preserve and do justice to these unique cultural works and their creators brings its own rewards.

Nigel Bryant – Audiovisual Digitisation Officer, University of Bristol Theatre Collection