While this medium is not widely used for audio or video, there is, I suspect, still a large amount of ancillary data kept in this format. I will look through my collection and see if there is anything else I need to capture to my servers before my drives die.  I would not entrust anything important to this format.

We stopped using these about three or four years ago, with the last holdout being school work brought home. Now, even that is done on USB keys.

I received an urgent phone call yesterday from a man who had digitized several reels of 2″ 24-track analog recordings that he wished to re-mix.

The tapes were originally recorded in about 1978-1979 and he said that he needed them to have Dolby C noise-reduction processing applied to the files.

I did a bit of research, as that did not sound correct from an historic point of view.

Here is an approximate chronology of the major noise-reduction systems and their dates of introduction:

DOLBY
A – 1967 (pro)
B – 1971 (consumer)
C – 1983 (consumer/prosumer)
SR-1986 (pro)
S – 1990 (consumer/prosumer)

dbx
I (pro) & II (consumer) – 1971

Telefunken (later ANT)
C4 – 1977

He later wrote me back saying the engineer was pretty sure it was Dolby A.

When I applied Dolby A, Dolby B, Dolby C, dbx I, and Telcom C4, only the dbx I sounded close to correct.

Fortunately, dbx I is less critical than the Dolby noise reduction systems for accurate level setting, since there are no test tones digitized along with the audio.

This work requires playing the digital files out through the D-A converter and then re-recording them via the A-D converter.

I recently unearthed 26 brand new 10 1/2-inch reels of 456 from 8 different batches. I checked one reel from each batch by playing them back and forth at 15ips (I only played the bad reels in one direction – that was enough!). The following batches were bad:

90297, 91049, 91055, 91079 and 91149

The following were fine:

94132, 94133, 94298 and 96190

The reels that were bad did not squeal during playback, but left debris on the heads and guides that was just barely sticky, so these are obviously in the beginning stages of deterioration.

All of these were Ampex (pre-Quantegy) tapes purchased in the early 1990s. Batch 96190 have lighter grey boxes as opposed to the textured, darker grey background found on the earlier batches, and the reel labels appear to be silk screened, rather than having sticker labels. None of these reels have the old rainbow-style logo.

I would guess that the good batches will probably remain OK – they’ve had a good 17 years to go bad and would probably have done so by now if there was a problem.

For whatever it’s worth…

Gary Galo
Audio Engineer
SUNY Potsdam
…speaking for himself

At some point, this tape was played on a 1/4-track machine that injected hum onto the left channel. Here’s what the magnetic viewer showed:

At the very top we can see a remnant of the left channel material, then the 120-Hz bars (62.5 mil spacing), then the remainder of the left channel material. In the middle is the guard band and at the bottom, the right channel.

Using a specially manufactured (by JRF Magnetics) assembly that contains a 4-channel 8-track head with a continuously variable height adjustment, we were able to lower the track one head to the middle of the good portion of the left channel. With that height positioning, track five’s head was well into the right channel, so we got a good transfer without the hum.

We believe this hum was written by the record head due to a malfunction in the recorder rather than an intentional erasure. If there had been an erasure, more of the left channel would have been erased and there would be a guard band between hum bars and the left channel audio as almost all erase heads were wider than the audio heads.

This type of damage is all too common using old consumer tape machines for playing tapes. I had an old junker machine in the 1960s that did this once to a tape. Unfortunately, it was also a quarter-track recording, so it was gone.

The magnetic record is fragile.

The Lunar Orbiter tape digitization folks have just posted a commentary that bears reading by all archivists who are holding tapes. You may link to it here. The main site is www.moonviews.com

NASA, in their press conference yesterday held at The Newseum, admitted that the original 14-track 1-inch instrumentation (IRIG) tapes that contained the slow-scan video direct from the moon were most likely recycled and reused for later missions. Apparently, over 350,000 reels of instrumentation tape were recycled by NASA over time. No one apparently thought to preserve the 45-odd reels of the original moon walk.

The loss of the original IRIG tapes of the moonwalk is truly sad because this data could be re-converted to standard television formats using far superior methods than were available in 1969. There may be 2-inch helical Ampex VR-660 video tapes still extant of the slow-scan data,  but those have not surfaced. It appears that all surviving copies of the moonwalk videos are ones that had gone through optical standards converters. An optical standards converter is one that has a monitor displaying the image in real time in the transmitted standard and a television camera taking a picture of that monitor using the desired standard. Even the Australian Broadcasting Corp. tapes would have gone through this type of device, although they would be in PAL rather than the U.S.’s NTSC versions.

Lowry Digital is doing a great job of restoring what they have, but the Polaroid screen shot that survives of the slow-scan monitor is alluring of what could have been preserved. More information is available on the Parkes website and from NASA.

Vigilant migration of data as new storage techniques become available is the only way to assure long-term preservation. Even if the IRIG tapes are found, we are almost at the point where the tapes would be un-decipherable. I think one of my machines could play them (I say think as I’ve never tested it to full 500 kHz bandwidth), but I don’t have the specialized video decoder. NASA apparently preserved some equipment should the tapes ever show up.

This also raises another spectre. We MUST be selective as to what we keep in our archives because if we keep everything we won’t be able to afford it–or find it. This is one of the key jobs that archivists do. However, blindly following retention practices, as was done by NASA for the IRIG Apollo 11 tapes, needs to be tempered by historians as well. Certain small subsets of data (moonwalk slow scan video) are much more important than others (astronauts’ blood pressure and other biometrics throughout the entire flight).

All organizations who keep archives need to address this. In a generation (or less) if we save everything, it will become an overwhelming burden and the high points will be lost if they are not properly indexed.

As with much equipment–and especially with lower-cost equipment–the performance specifications and the actual operational data is not published. There are reports of the H2 clipping on the line inputs in some of the reviews and it appears that a lack of understanding how the inputs were configured exacerbated that situation.

There is nothing wrong with the line inputs on the H2. BUT there are some caveats:

1. DO NOT use the input level control on the line inputs to go below 100 or the preamps will clip before the signal reaches 0 dBFS.
   ALTERNATE WORDING (thanks Greg H.):
   Set Zoom H2 RECORD LEVEL to 100 or greater to avoid clipping at the Line In preamp stage.
2. Use an external attenuator with the gain set at 100 to avoid overdriving the line inputs.
3. The noise floor is not spectacular, but is not too bad. With the inputs terminated in 150 ohms, the peak noise was -70 dBFS, but that improved to about -85 dBFS or better, measuring it as an A-weighted rms figure, which is how most noise is measured. While this certainly isn’t what one would expect out of the Sound Devices, it is far better than the 50-60 dB(A) that one can achieve with an analog cassette tape without Dolby.
4. The maximum input level to the line input should be no more than -5 dBV or -3 dBu.
5. Try to avoid clipping as there appears to be a delayed recovery in some instances.

With this information, you can optimize a pad between the source and the H2 line input so that the recorder is never overloaded. Try to keep the levels as high as practical as there is a relatively limited dynamic range. On the other hand, I have found that the recorder noise is not objectionable even when I’ve boosted the levels 20 dB for a quiet choir piece from our church. The room ambience totally swamps the recorder noise–at least as far as I hear.

The H2’s internal mics are reasonably good for many purposes. While I still prefer the SD722 for many things, I think the H2 is one of the better oral history conversation capturing devices I’ve seen. It uses SDHC cards which may require a new card reader. Don’t use the built-in USB connection unless you’re recording MP3 files as you’ll be there all day. The internal card-reader mode is limited by the USB 1.1 interconnection. This interconnection is adequate, however, for using the H2 as a 16-bit live audio interface/microphone connected to your computer (at either 44.1 or 48 ks/s). The unit will record up to 96,000 samples per second, 24 bits,  but many of those bits will be noise.

Please let me know if this has helped or if you have any questions or comments.This work was done with version 1.50 of the H2 firmware.

These tapes were badly warped due, most likely, to the vinegar-syndrome induced differential shrinkage. Other factors may have been poor winding during long-term storage (I had received them after several attempts to play them on another machine).

Not only was the tape cupping about its centre axis (with the basefilm shrinking so the edges were pulling back from the tape plane (away from the heads), it also had extremely wavy edges. In addition, the tapes would not lie flat on the reel due to the dimensional changes that were strongly embedded in the tapes.
We were able to play this tape on our stereo (NAB) A80, but discovered it was a 1/4 track tape (the original source had said it was half-track mono). We elected to stay with the A80 because:

• The A80 has the stabilizer roller which tends to “break the back” of cupping
• We had already adjusted the machine to have substantially higher tension to help flatten the tape–this was clearly a case of wanting the knobs to go to 11 or 12, but we had to settle for 10 on the play tensions.
• We do not have a four-track head for this machine AND the machines for which we have compatible heads do not have as easily adjustable tensions or the ability to safely set the tensions as high as we did on the A80
• The original recording was off-air AM radio after a trip of 1,000 miles through landline telco audio networks from 1964

So while the reproduction was only fair, we maintained good tape-to-head contact despite the inability to play this tape on other machines. If the content had been better fidelity and the client had been willing to pay for mounting a four-track head on the A80, we might have achieved some improved noise performance, but the original recording was quite low level (even correcting for the 1/4 track mismatch). Depending on segment, VU meter zero for the quarter track recording was somewhere around 15 nWb/m! We could hear recorded hiss,  however, over the tape noise even in this configuration!

We were able to improve listenability by using a filter that matched the playback bandwidth to the recorded bandwidth (it appeared to be about 200-3500 Hz, we filtered for 200-4000 Hz) and it sounded about as good as we would have expected hearing over a transistor radio in 1964. Further processing with Algorithmix Noise Free Pro reduced background noise (including random crowd noise, but not loud cheers–it was a football game) and made the announcers pop out more, so if someone is intent on listening to the details of what the announcers said, this would be easier to listen to, but less authentic to the sound of the original broadcast.

These tapes were transferred somewhere near their effective end-of-life. It would have been better if these tapes had been transferred 10-20 years ago. Based on other experience with Kodak tapes, I am not surprised with this. Interestingly, the Durol basefilm in its present state of decay was not translucent as most magnetic tapes are, so translucency of basefilm is not a 100% accurate test for acetate basefilm.

Use your browser back button to return to this page.
Here are the ones with the picture of the chamber orchestra
http://www.richardhess.net/restoration_notes/111.jpg (red 7″)
http://www.richardhess.net/restoration_notes/120.jpg (orangy-brown 7″)
http://www.richardhess.net/restoration_notes/200.jpg (blue 7″)
http://www.richardhess.net/restoration_notes/311.jpg (grey-green 5″)

The moiré pattern you may see is the screening of the printing beating with your monitor.

These are earlier boxes for two if the above
http://www.richardhess.net/restoration_notes/111(A)_early.jpg
http://www.richardhess.net/restoration_notes/120(A)_early.jpg

And then it all became standardized in the 1970-era box
http://www.richardhess.net/restoration_notes/200_1970.jpg

When I get a chance, I’ll scan the box between the musicians one and the 1970s one.

We hope to update this as we come across more types. January 2009 was, sadly, fruitful in finding at least some batch(es) of two tapes from 1990 (Agfa PEM 526) and 2003 (Emtec SM911) are degrading. The Emtec SM911 was thought to be more-or-less immune from this disease. As of this writing, it has been confirmed that batch number B0134007 was involved.

Agfa PEM-526 exhibited this odd behaviour. The tape was recorded in 1990.

There is also a discussion about PEM-469 showing similar behaviour here.

For a current list of degrading analog tapes, click here.

The British Libary has now published his Handbook (click here).

Teaching people how to identify tapes that are suffering from sticky shed syndrome is often difficult.

I would like to propose that a careful inspection of how the tape comes off the pack may be a good way. Please provide comments as to how it’s working for you.

The tape should come off the tape pack at a precise tangent to the tape. If the tape starts to adhere and not pull off straight, that is a sure sign that the tape needs baking.

Of course, don’t bake acetate tapes even if they show this indicator, but on the last batch of questionable SSS tapes, I’ve been looking at this and it’s a fair indicator, and it seems to show at the outer edge of the pack.

More than one “test” or “factor” is needed to be sure, but this one is looking good.

Another almost sure sign of SSS is brown oxide and black back-coat.

While this is a theoretical problem, few if any good mono recorders are available for reproducing these tapes anyway, so most of us in the domain transfer field use good quality stereo machines for all cassette transfer work.

This is an interesting anomaly that should not effect operations. If you had a full-width mono head, there would be at most about a 4 dB improvement in signal-to-noise ratio vs. using one track of a stereo head (which usually results in better sound). Since the premium cassette decks, such as the Nakamichi Dragons that I use, provide very low wow and flutter, flat frequency response, a means to adjust azimuth of the play head, and gentle tape handling, all of these benefits outweigh the 4 dB or less reduction in signal-to-noise performance. If the tape hiss is a real problem (as opposed to noise recorded in from the recorder’s electronics), some of it can be effectively removed using a noise-reduction plug-in. Generally a 4 dB noise reduction in a good plug-in is transparent.

We do recommend archiving both tracks in a professional archival scenario.

It appears that I am not alone in thinking this is a good product as it has resurfaced as the U-Print CDP78, now in black, and available from many online distributors. The cartridges appear to be interchangeable with the Primera. I can now suggest that this is a good alternative for safe, long-lasting, and reasonably attractive text labeling of CDs and DVDs. It appears that the Teac P11 is also similar. The last time I checked, the Casio required manual rotation of the disk, rather than the Primera’s automatic rotation.

Please provide me with any feedback pro or con—preferably as comments to this post.

The general theory behind a checksum (or “Message Digest” = “MD”) is that it provides a unique 128-bit number for each and every file, based on its content. If one bit changes, the MD5 checksum (sometimes called “hash”) changes. The checksum is repeatable, does not permit discovery of two different files that produce the same checksum, and is non-reversible (i.e. you can’t create the content from the checksum).

Common practice in audio archiving is to use 128-bit checksums, although 160-bit checksums are available. The other common practice is to take the entire filename, including extension, and add a second “MD5″ extension to that. The *.*.md5 file contains the MD5 checksum plus generally the filename.

An alternate configuration is to create one file named checksums.md5 for the entire folder to save downloading effort.

While there are many options for creating MD5 checksums, for Windows, FastSum is a convenient and low-cost package.

At any point in the future, to verify your files, you create a new MD5 checksum and compare it to the ones that were created when the file was created. If they match, you know your file has not changed. The likelihood of both the original file and the checksum file changing so that they still appear valid is essentially nil.

Some applications, like D-Space, check the integrity of all the files in the system on a regular basis using MD5 checksums.

If you receive WAV files from me, more than likely, you will also receive MD5 checksums in the same package, be that on a DVD, hard drive, or via the Internet.

It only takes a minute to create these and it truly does offer peace of mind.

I have just completed about 25 seven-inch reels of circa 1960-1965 acetate tapes (Scotch 111A, Audiotape, Soundcraft, Ampex 511, etc.) and about 20% of the tapes showed evidence of spoking after being played on the A80. These were rewound (approx 120 in/s under capstan control) on the Racal Store 4DS and then played at 15 in/s back onto their original spool.

With the heads removed, there are no fixed guides that contact the tape, just the two rolling tension guides and the capstan.

For photos of the Racal Store 4DS, please look here where I discuss its use (with head/guide assembly) for playing squealing tapes.

Please also read this post for a “do not try this at home” note.

I had the pleasure of speaking with Nadja at length about her work and I was very impressed by her approach and knowledge — as well as her practicality in getting the job done.

This document is a must-read for anyone planning a digitization project. While it is not as detailed or comprehensive as the Sound Directions publication, it cuts to the heart of what we’re trying to do in digitization. Starting with as good a playback as possible is the key to obtaining a good digital representation of the original. It also provides excellent photographs of various failure modes — and some are truly spectacular.

I must provide a disclaimer here that this website graciously links back here as well.

Oh, and the discussion started about images, but it pertains equally to audio and video. Ike was certainly clear on his thoughts about data tape. As I see it (without following it too closely), the marketplace is consolidating around LTO and appears to be shrinking, so maybe he’s right. I’ve stayed away from data tape in favour of an all-disk solution (for approximately 3 TB of storage at the moment).

When looking at storage for audio, consider a track-hour (i.e. a mono program) at 96,000 samples per second, 24 bits, is about 1 GB, uncompressed. 1 TB is about 1,000 track-hours of material at the normal high-resolution sample rate and bit depth…and that currently fits on one physical drive.

We continue to receive poorly wound tapes and are able to play them successfully. So why the quandary now? The reason is that I read portions of another Bharat Bhushan book, Mechanics and Reliability of Flexible Magnetic Media, 2nd Edition, New York, Springer, 2000. Referring to several research papers he makes a compelling case that tapes should be rewound annually if subject to storage environment fluctuations and every 3.5 years if kept in a climate controlled storage area.

If we think about the two types of stresses on each layer in the pack, this becomes more clear. There are “hoop stress” which is the circumferential stress in that individual layer and the “radial stress” which is the stress in the direction of the centre hub.

Low interlayer pressures, which predispose the tape stack to ILS [Interlayer Slip], are created as follows: the winding of successive layers of tape onto a reel increases the radial compressive stresses in the wraps of tape at and near the hub. The continued inward radial deflection of the hub converts the circumferential tensile strain in the tape, originally caused by winding, to a compressive strain….The tape, hub, and winding parameters sufficient to obtain this condition can be determined using [the complex] analysis presented in Chapter 5. A highly compressible hub, high outer-wrap winding tension, low inner-wrap winding tension, the length of tape stored on a reel, and the entrapment of air during high-speed winding are strong contributors to low interlayer pressure

The interlayer pressure from winding is further reduced by temperature and humidity cycling and/or storage….The interlayer pressure can be reduced when the wound tape is subjected to a temperature of humidity change, and is dependent on the relative value of the coefficients of thermal and hygroscopic expansion of the hub and the tape. This effect is aggravated not only by the magnitude of this differential mismatch, but also by the mismatch in the tape’s radial and circumferential coefficients of thermal and hygroscopic expansion.

Bhushan also indicates that spoking can be triggered by impact forces to the tape reel. (Dropping it?)

One of the very interesting things which is discussed is that a tapered winding tension may produce a more archival tape pack than a constant tension winding tension. This raises many questions concerning current archival practices.

I suspect that more discussion of this will occur. Please leave your comments.