time base corrector

Digitisation: methodologies, processing and archival practices

 Time-based correction machinesWe work with a range of customers at Great Bear, digitising anything from personal collections to the content of institutional archives. Because of this, what customers need from a digitisation service can be very different.

A key issue relates to the question of how much we process the digital file, both as part of the transfer and in post-production. In other words, to what extent do we make alterations to the form of the recording when it becomes a digitised artifact. While this may seem like an innocuous problem, the question of whether or not to apply processing, and therefore radically transform the original recording, is a fraught, and for some people, ethical, consideration.

There are times when applying processing technologies is desirable and appropriate. With the transfer of video tape, for example, we always use time-based correctors or frame synchronisers to reduce or eliminate errors during play back. Some better quality video tape machines, such as the U-matic BVU-950P, already have time-based correctors built in which makes external processing unnecessary. As the AV Artifact Atlas explains however, time-based correction errors are very common with video tape:

‘When a different VTR is used to playback the same signal, there can be slight mechanical and electronic differences that prevent the tape from being read in the same way it was written. Perhaps the motors driving the tape in a playback VTR move slightly slower than they did in the camera that recorded the tape, or maybe the head of the playback VTR rotates a fraction quicker than the video head in the machine that recorded the tape. These tiny changes in timing can dramatically affect stability in a video image.’

We also utilise built in processes that are part of machine’s circuitry, such as drop out compensation and noise reduction. We use these, however, not in order to make the tape ‘look better.’ We do it rather as a standard calibration set up, which is necessary for the successful playback of the tape in a manner appropriate to its original operating environment.

After all, video tape machines were designed to be interchangeable. It is likely such stabilising processing would have been regularly used to play back tapes in machines that were different to those they were recorded on. Time-based correction and frame synchronisation are therefore integral to the machine/ playback circuitry, and using such processing tools is central to how we successfully migrate tape-based collections to digital files.

Digital processing tools Time Based Correction - Close Up

Our visual environment has changed dramatically since the days when domestic video tape was first introduced, let alone since the hay day of VHS. The only certainty is that it will continue to change. Once it was acceptable for images to be a bit grainy and low resolution, now only the crisp clarity of a 4K Ultra HD image will do. There is perhaps the assumption that ‘clearer is better’, that being able to watch moving images in minute detail is a marker of progress.  Yet should this principle be applied to the kinds of digitisation work we do at Great Bear? There are processors that can transform the questionable analogue image into a bright, high definition, colour enriched digital copy. The teranex processor, for example, ‘includes extremely high quality de-interlacing, up conversion, down conversion, SD and HD cross/standards conversion, automatic cadence detection and removal even with edited content, noise reduction, adjustable scaling and aspect ratio conversion.’ ‘Upgrading’ analogue images in this way does come with certain ethical risks.

Talking about ethics in conjunction with video or audio tape might seem a bit melodramatic, but it is at the point of intervention/ non-intervention where the needs of our customers diverge the most. This is not to say that people who do want to process their tapes are unethical – far from it! We understand that for some customers it may be preferable for such processing to occur, or to apply other editing techniques such as noise reduction or amplification, so that audio can be heard with greater clarity.

Instead we want to emphasise that our priority is getting the best out of the tape and our playback machines, rather than relying on the latest processing technology that is also at risk from obsolescence. After all, a heavily processed file will always require further processing at an unknown point in future so that it can maintain visually relevant to whatever format is commercially dominant at the time. Such transformations of the digital file, which are necessarily destructive and permanent, contribute to the further circulation of what Hito Steyerl calls ‘poor images‘, ‘a rag or a rip; an AVI or a JPEG…The poor image has been uploaded, downloaded, shared, reformatted, and reedited. It transforms quality into accessibility, exhibition value into cult value, films into clips, contemplation into distraction.’

Maintaining the integrity, and as far as possible authenticity of the original recordings, is a core part of our methodology. In this way our approach corresponds with Jisc’s mantra of ‘reproduction not optimisation’ where they write:

‘Improving, altering or modifying media for optimisation may seem logical when presenting works to a public or maintaining perceived consistency. It should be remembered that following an often natural inclination to enhance what we perceive to be a poor level of quality is a subjective process prescribed by personal preference, technological trends and cultural influences. In many cases the intentions of a creator are likely to be unknown and this can cause difficulties in interpreting levels of quality. In these instances common sense alongside trepidation should prevail. On the one end of the spectrum unintelligible recordings may be of little use to anyone, whereas at the opposite end recordings from previous eras were not produced with modern standards of clarity in mind.’

It is important to bear in mind, however, that even if a file is subject to destructive editing there may come a time when the metadata created about the artefact can help to illuminate its context and provenance, and therefore help it maintain its authenticity. The debates regarding digital authenticity and archiving will of course shift as time passes and practices evolve.

In the meantime, we will continue to do what we are most skilled at: restoring, repairing and migrating magnetic tape to digital files in a manner that maintains both the integrity of the original operating environment and the recorded signal.

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

Video time base corrector self destructing mains socket

Filtered mains socket self destructs in CEL TBC

We have several time base correctors and frame synchronisers at our disposal. One recent addition is a new old stock (NOS) CEL Tetra. This is an early 1990’s motion adaptive Standards Converter for PAL, SECAM, NTSC 3.58 and NTSC 4.43 systems. A very flexible unit with composite, Y/C (S-Video), umatic DUB High Band/Low Band and component inputs and outputs.

Out unit still has it’s shipping caps over the BNC sockets and looks unused but after 5 minutes of power a cloud of white smoke billowed out of the cooling fan accompanied by a pungent smell. The Shaffner EMI mains filter had a nasty, sticky brown residue leaky out and all around the back of it. This is the second TBC that I’ve had this happen to. I’d assumed these units get left on for long periods when used in broadcast applications which would hasten their demise. According to their website, the mean time between failures (MTBF) of their recent products is around 2,000,000 hours! Our CEL TBC doesn’t look like it’s done more than 30 minutes so maybe there’s been some dodgy electrolytic fluid in these units just like the motherboard capacitor problems between 2000 and 2003.

Posted by greatbear in Video Tape, 1 comment