wow / flutter

Audio Cassette Parallel Ingests

The scale of digitisation jobs we do at Greatbear often varies. We are asked by our customers to reformat single items to large quantities of tape and everything else inbetween.

Reformatting magnetic tape-based media always takes time and care.

Transfers have to be done in real time; if you want a good quality recording there is no way to reformat tape-based media quickly.

Some jobs are so big, however, that you need to find ways of speeding up the process. This is known as a parallel ingest – when you transfer a batch of tapes at the same time.

Realistically, parallel ingest is not possible with all formats.

An obvious issue is machine scarcity. To playback tapes at the same time you need multiple playback machines that are in fairly good condition. This becomes difficult with rarer formats like early digital video tape, such as D1 or D2, where you are extremely lucky if you have two machines working at any given time.

Audio Cassettes

Audio cassette tapes are one of few formats where archival standard parallel ingest is possible if tapes are in good condition and the equipment is working well.

Stack of professional tape machines, including Marantz PMD 502 and Tascam 322

Great Bear Parallel Ingest Stack

We were recently approached by Jim Shields of the Zion, Sovereign Grace Baptists Church in Glasgow to do a large scale transfer of 5000 audio cassettes and over 100 open reels.

Jim explains that these ‘tapes represent the ministry of Pastor Jack Glass, who was the founder of Zion, Sovereign Grace Baptists Church, located at Calder St.Polmadie, Glasgow. The church was founded in 1965. All early recordings are on reel but the audio tapes represent his ministry dating from the beginning of 1977 through to the end of 2003. The Pastor passed away on the 24th Feb 2004 [you can read obituaries here and here]. It is estimated there are in the region of 5,000 ministry tapes varying in length from 60 mins to 120 mins, with many of the sermons being across 2 tapes as the Pastor’s messages tended to be in the region of 90 minutes plus.’

Sermons were recorded using ‘semi domestic to professional cassette decks. From late Sept 1990 a TEAC X-2000 reel recorder was used [to make master copies] on 10 inch reels then transposed onto various length cassettes [when ordered by people]’ chief recordist Mike Hawkins explains.

Although audio cassettes were a common consumer format it is still possible to get high quality digital transfers from them, even when transferred en masse. Recordings of speech, particularly of male voices which have a lower frequency range, are easier to manage.

Hugh Robjohns, writing in 1997 for the audio technology magazine Sound on Sound, explains that lower frequency recordings are mechanically more compatible with the chemical composition of magnetic tape: ‘high-frequency signals tend to be retained by the top surface of the magnetic layer, whilst lower-frequency components tend to be recorded throughout its full depth. This has a bearing on the requirements of the recording heads and the longevity of recordings.'[1]

Preparation

In order to manage a large scale job we had to increase our operational capacity.

We acquired several professional quality cassette machines with auto reverse functions, such as the Marantz PMD 502 and the Tascam 322.

Although these were the high end audio cassette recorders of their time, we found that important components, such as the tape transport which is ‘critical to the performance of the entire tape recorder'[2], were in poor shape across all the models. Pitch and timing errors, or wow (low speed variations) and flutter (high speed variations), were frequently evident during test playbacks.

Because of irregular machine specifications, a lot of time was spent going through all the tape decks ensuring they were working in a standardised manner.

In some cases it was necessary to rebuild the tape transport using spares or even buying a new tape transport. Both of these restoration methods will become increasingly difficult in years to come as parts become more and more scarce.

Assessing the options

There are certainly good reasons to do parallel ingests if you have a large collection of tapes. Nevertheless it is important to go into large scale transfers with your eyes open.

There is no quick fix and there are only so many hours in the working day to do the transfers, even if you do have eight tapes playing back simultaneously.

To assess the viability of a large scale parallel ingest you may want to consider the following issues: condition of tapes, how they were originally recorded and the material stored on them.

It may well be that parts of your collection can be reformatted via parallel ingest, but other elements need to be selected for more specialist attention.

As ever we can help with discussing the options so do contact us if you want some specific advice.

Notes

[1] The gendered implications of this statement are briefly worth reflecting on here. Robjohns suggests that voices which command the higher frequencies, i.e., female or feminine voices, are apparently incompatible with the chemical composition of magnetic tape. If higher frequencies are retained by the top layer of magnetic tape only, but do not penetrate its full depth, does this make high frequencies more vulnerable in a preservation context because they never were never substantially captured in the first place? What does this say about how technical conditions, whose design has often been authored by people with low frequency voices (i.e., men), privilege the transmission of particular frequencies over others, at least in terms of ‘depth’?

[2] Hugh Robjohns ‘Analogue Tape Recorders: Exploration’ Sound on Sound, May 1997. Available: http://www.soundonsound.com/sos/1997_articles/may97/analysinganalogue.html.

*** Many thanks to Jim Shields, Martyn Glass and Mike Hawkins for sharing their tape stories***

Posted by debra in audio tape, 0 comments

Digitising Audio Tape – Process, Time & Cost

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.

Let’s 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

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.

Wow-and-flutter-monitor

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.

Posted by debra in audio tape, 2 comments

Replace Tascam BR 20 Capstan Belt

We have two of these excellent machines in addition to our Sony APR 5003s and Studer A80s. The Tascam BR-20 was Tascam’s last and top of the range 1/4 inch reel to reel tape machine and available in two track stereo and stereo with centre timecode option.

The capstan drive in the BR20 is belt driven by a wide belt. Both belts in our machines looked OK but we’ve replaced all roller bearings, belts and pinch rollers in both of our machines anyway as a matter of course. These parts are still available from Teac UK via Acoustic Services on 01-844-347600.

Below is a simple explanation of how to change the capstan belt.

Tascam / Teac BR 20 rear panel removed

  1. Unplug machine from mains power and move to a strong stable base.
  2. Remove cross head screws from the rear panel and lift plate off. Depending on the type of plug in your country you may not be able to remove it completely.
  3. You’ll now be able to see the capstan motor and it’s control board attached to it.
  4. Remove the 4 cross head screws and gently lift the analogue audio output board away from the machine as in the picture above.
  5. We now need to remove the whole capstan motor assembly with the control board still attached. Remove the 4 cross head screws right at the front of the assembly, NOT the six nearest to you when looking at this image. 
  6. Carefully unclip the 4 cable connectors from the motor control board. The other connector cannot be removed from the board and must be removed where it connects to the other board.Tascam BR 20 capstan motor board with cables removed
  7. The whole assembly can now be lifted out from the machine. Be careful to not snag any cables and remember to unclip the black cable ties.
  8. You’ll now be able to unclip the control board from the assembly by carefully compressing the black clips with some needle nose pliers.
    Tascam BR 20 capstan motor board unclipped from assembly
  9. Now remove the six cross head screws holding the capstan motor assembly together. This is the only way to remove and refit the capstan belt. There’s not enough room to do it any other way!
  10. Now you can remove the old belt and capstan shaft. It’s a good idea to clean the capstan with IPA where the old belt has run and reapply a little grease to the bearing end of the capstan.
  11. Fit your new belt and reassembly is the reverse of dissasembly! Be careful though to not drop the screws into regions you can’t get them out of – luckily there aren’t that many on this machine but a long magnetic screwdriver is very useful.. just don’t get it anywhere near the headblock and heads!
    New Teac capstan belt for Tascam BR20 reel to reel tape machine
Posted by greatbear in audio tape, audio technology, machines, equipment, 2 comments