Posts Tagged ‘alignment’

Paul Roche recordings & preservation challenges with acetate reel-to-reel magnetic tape

Monday, November 25th, 2013

We were recently sent a very interesting collection of recordings of the late poet, novelist and acclaimed translator Paul Roche. During his colourful and creative life Roche published two novels, O Pale Gallellean and Vessel of Dishonour, and several poetry collections, and brushed shoulders with some of the 20th century’s most captivating avant-garde artistic and literary figures. His faculty colleague when he worked at Smith College, MA in the late 1950s was none other than Sylvia Plath, who pithily described Roche’s ‘professional dewy blue-eyed look and his commercially gilded and curled blond hair on his erect, dainty bored aristocratic head’.

His intense 30 year friendship with painter Duncan Grant was immortalised in the book With Duncan Grant in Southern Turkey, which documented a holiday the friends took together shortly before Grant’s death. The relationship with Grant has often eclipsed Roche’s own achievements, and he is often mistakenly identified as a member of the Bloomsbury group. Roche also achieved success beyond the literary and scholarly world when his translation of Oedipus the King became the screenplay for the 1968 film starring Christopher Plummer and Orson Welles.

The recordings we were sent were made between 1960-1967 when Roche worked at universities in America. Roche experienced greater professional success in America, and his translations of Ancient Greek are still used in US schools and universities. His son Martin, who sent us the tapes, is planning to use the digitised recordings on a commemorative website that will introduce contemporary audiences to his father’s creative legacy.

The Great Bear Studio has been pleasantly awash today with the sound of Roche reading poetry and his dramatic renditions of Sophocles’ ‘Oedipus the King’, ‘Oedipus at Colonus’ and ‘Antigone’. The readings communicate his emphatic pleasure performing language via the spoken word, and an unique talent to immerse listeners in images, rhythm and phrases.

Listen to Paul Roche reading his translation of ‘Antigone’.

Our own pleasure listening to the recordings has however been disrupted because of frequent snaps in the tape. The tapes are covered in splices, which suggests they had been edited previously. Over time the adhesive glue has dried out, breaking the tape as it moves through the transport. The collection of tapes as a whole are fairly brittle because the base film, which forms the structural integrity of the tape, is made of acetate.

Canadian-based digitisation expert Richard Hess explains that

‘Acetate was the first widely used base film, with Scotch 111 being in production from 1948 through 1972/73, a total of 24-25 years. Acetate tape is generally robust and has the advantage of breaking cleanly rather than stretching substantially prior to breaking when overstressed. Acetate tapes residing in collections are over 30-years-old, with the oldest being over 60-years-old.’

The big downside to acetate is that when it degrades it loses its flexibility and becomes a bit like an extended tape measure. This means it is harder to pass the tape consistently through the tape transport. This is colloquially known in the digitisation world as ‘country-laning’, when the tape changes shape in all dimensions and becomes wiggly, like a country lane. To extend the metaphor, a well functioning tape should be flat, like, one supposes, a motorway.

IMAG0332 1024x707 Paul Roche recordings & preservation challenges with acetate reel to reel magnetic tapeWhen a tape is ‘country-laning’ it means tracks of recorded material are moving slightly so they shift in and out of phase, dis-aligning the angle between the tape head(s) and tape, or azimuth. This has a detrimental effect on the quality of the playback because the machine reading the recorded material on the tape is at odds with surface area from which the information is being read.

If you are reading this and wondering if the base film in your tape is made of acetate, or is made of another substance such as paper or polyester, you can perform a simple test. If you hold the tape against the light and it appears translucent then the tape is acetate. There may also be a slightly odd, vinegar smell coming from the tape. If so, this is bad news for you because the tape is probably suffering from ‘Vinegar Syndrome’. Richard Hess explains that

‘Vinegar syndrome occurs as acetate decomposes and forms acetic acid. This is a well-known degradation mode for acetate film. High temperature and humidity levels, the presence of iron oxide, and the lack of ventilation all accelerate the process. Once it has started it can only be slowed down, not reversed.’

Acetate tape is also particularly vulnerable to excessive heat exposure, which makes it shrink in size. This is why you should never bake acetate tape! When acetate tape is exposed to heat it reaches what is known as the liquid-glass transition phase, the temperature where the material composition starts to change shape from a hard and relatively brittle state into a molten or rubber-like state. Although glass transition is reversible, it certainly is destructive. In other words, you can change the tape back from molten to a hard substance again but the tape would be unplayable.

While acetate backed tape has certain advantages over polyester tape in the migration process, namely it is easier to cleanly splice together tape that has broken as it has moved through the transport, unfortunately acetate tape is more fragile, and can get extremely stiff which makes it difficult to play back the tape at all. Even if you can pass the tape through the machine it may snap regularly, and will therefore require a lot of treatment in the transfer process. So if you have a valuable tape collection stored predominantly on acetate tape, we strongly recommend getting it migrated to digital format as soon as possible due to the fragility of the format. And if that whiff of vinegar is present, you need to move even more quickly!

Digitising Audio Tape – Process, Time & Cost

Monday, June 10th, 2013

Last week we wrote about the person time involved in transferring magnetic tape to digital files, and we want to tell you more about the processes involved in digitisation work.

While in theory the work of migrating media from one format to another can be simple, even the humble domestic cassette can take a substantial amount of time to transfer effectively.

Doing transfers quickly would potentially keep the costs of our work down, but there are substantial risks involved in mass migrations of tape-based material.

Problems with digital transfers can occur at two points: the quality of the playback machine and the quality of the tape.

First, lets focus on the playback machine.

Each time a cassette is transferred we have to ensure that the cassette deck is calibrated to the technical specification appropriate to that machine. Calibration is a testing procedure where a standard test tape is used to set the levels for tape to be digitised. The calibration process allows us to check tapes are played back at the correct speed and audio levels, that wow and flutter levels are set and the azimuth is aligned.

Azimuth refers to the angle between the tape head(s) and tape. Differences in Azimuth alignment arise from the azimuth of the original recording. You cannot know this information from just looking at a tape and you will get a sub-optimal transfer unless you adjust your machine’s azimuth to match the original recording.

sony apr 5003 headblock azimuth Digitising Audio Tape   Process, Time & Cost

Regularly checking the Wow and Flutter on the tape machine is also very important for doing quality transfers. Wow and flutter refer to fluctuations in speed on the playback mechanism, flutter being a higher rate version of wow. If you have listened to a tape you will probably be familiar with the sound of warped and woozy tape – this is the presence of wow. All tape machines have wow and flutter, but as components in the mechanisms stretch there is the potential for wow and flutter to increase. It is therefore essential to know what level the wow and flutter are set on your tape deck –less than 0.08% Weighted Peak on our Nakamichi 680 machines – to ensure optimal transfer quality.

Not all cassette machines were made equal either, and the quality of playback is absolutely dependent on the type of machine you have. There is a massive difference between the cheap domestic cassette machines made by Amstrad, to the cassette decks we use at Great Bear. Nakamichi machines were designed to squeeze the most out of the cassette, and their performance is way above the standard ‘two head’ cheap domestic machines.

Even with a Nakamichi deck, however, they have to be regularly checked because they are fragile electromagnetic machines that will drift out of specification over time. When machines drift they slip out of alignment, therefore effecting their operating capacity. This can occur through subtle knocks, everyday wear and tear and general ageing of mechanical and electrical components. For example, with extended use the grease in the components dries up and goes hard, and therefore affects the movement of the mechanisms.

DSC01337 1024x680 Digitising Audio Tape   Process, Time & Cost

Problems can also arise with the tapes themselves.

Most issues arise from tapes not being played back in well calibrated machines.

With audio cassettes the potential for azimuth error is increased because the speed the tape moves pasts the head is very slow. The tape therefore needs to be assessed to see if it is in a playable condition. It is played back in mono because it is easier to hear if there are problems with the azimuth, and then the azimuth is manually adjusted on the machine.

Migrating tape is unquestionably a ‘real time’ process. You need to listen and monitor what’s on the tape and the digitised version to ensure that problems with the transfer are detected as it is happening. It is a very hands on activity, that cannot be done without time, care and attention.

azimuth adjustment when you transfer and convert cassettes to cd

Friday, October 21st, 2011

Cassette tapes run at a very slow speed of 1 7/8′s inches per second (ips) with a very small track width of 1.59mm

Cassette decks when they left the factory or a service centre should have been aligned to a standard reference for the position of the record and play heads. Unfortunately they often weren’t all the same and over time the alignment can get drift, get knocked out or manual ‘fiddled with’ by an owner.

What this means is that unless you’re playing back your tape on the machine it was originally recorded on you may be getting the maximum quality as the angle of the head to the recording or azimuth will not be optimal.

Without calibration tones recorded at the start of the tape which is very unlikely on most domestic cassette tape recordings you must set the playback azimuth manually. A few high end tape decks, namely those made by Nakamichi, either had a easily accessed Azimuth adjust or could even automatically adjust this throughout the tape. The Nakamichi Dragon was one such tape deck and could be the best, if working well, for high quality playback.

If you want to transfer or convert a cassette to CD and adjust the azimuth yourself this is the an easy way to do it:

  1. Look at the tape path (everything the tape will move across) and if it looks brown and dirty get some isopropyl alcohol and give it a good clean with a cotton bud.
  2. If you haven’t demagnetised your deck for a while now would be a good time to do it..
  3. Power up your cassette deck, which hopefully works correctly and doesn’t have too much speed instability!
  4. Pop your tape in the cassette well and start to play.
  5. Turn your amplifier’s volume up and if you can put it in Mono.
  6. Now, look under the tape machine’s playback or combined record and playback heads you should see a small screw or nut possibly with anti tamper paint on it.
  7. Using an appropriate tool, turn this nut or screw a little left or right while listening to the audio.
  8. You should hear the recording, especially if it has a lot of high frequency content such as cymbals etc get bright and dull sounding or more technically get more in or out of phase.
  9. Your aim is to get the most in phase or bright sounding playback.
  10. Sounds better now?? Great, start to record using you favourite computer audio software. We like SoX for the control but there’s a huge range out there.

 

Information Terminals M-300, cassette tape transport alignment gauge

Saturday, November 21st, 2009

The regular service of analogue machines which will involve the mechanical alignment then electrical alignment / calibration is really important if you’re attempting to get optimum transfers and reduce any risk of damaging the potentially fragile tape.

While some of our machines are serviced by others we like to regularly check them and have gradually bought our regular servicing in house. Of course this needs specialised tools, test tapes and gauges, often totally unavailable new now.

On a lucky eBay day I happened to win one of these beauties, an Information Terminals M-300 gauge. This enables you to accurately set the tape guide height and also the head stroke. It is a universal gauge and can be used across many decks.

information terminals m300 boxed copy 791x1024 Information Terminals M 300, cassette tape transport alignment gauge

Nakamichi tape deck owners have had a hard time doing this part of their servicing as the original Nakamichi gauges are very very rare now as is this.

A member of the naktalk mailing list though recently borrowed our gauge and has had it measured and will soon have a small batch CNC machined and made available. These remanufactured gauges will have a few small modifications to improve the design.

Thanks to Willy at www.willyhermansnervices.com many more tape deck transports will be able to be aligned correctly.


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