The formats that I am still accepting are:
—Digital Files on CD, DVD, hard drive, USB drives, etc.
—CD
—MiniDisc (normal stereo, not porta-studio multitrack)
—PCM-F1 on VHS or Betamax
—Sony DASH (3202 or 3402) 2-channel reel

I will, however, attempt to play digital tapes in other formats that I used to accept as stand-alone projects if there are one or two in a larger collection that I am digitizing and the machine still works. These formats include:
—DAT
—Digital Compact Cassette (DCC)
—20-bit ADAT (8 track)
—DA-38/DA-88 DTRS tapes (8 track)

DATs have become especially problematic of late, and I have decided not to risk my remaining machines attempting to play them. I recently discovered, when attempting to play a client DAT, that two of my four machines, which I had considered backups, were non-functional after having been in storage for about a half-dozen years without use. I also have a personal collection of DATs that I need to transfer.

One thing that appears to be happening is that DAT tape may be in need of baking. I have had success with one tape, but more research needs to be done.

As with all formats, my ability to transfer them is limited by available working machines. While I did not make a big announcement about dropping 8-track analog cassettes, it was uneconomical to maintain the machine for that format as well, and I sold it.

I have listed other resources that might be of assistance on this link for dedicated digital audio formats and this link for digital audio formats that used an adapter with a VCR.

I provided some information for the listing of tape equalizations, and I find the compiled table (here) most useful.

Thanks to Kevin Bradley and the IASA team for their work in making this available. If you want a PDF copy, join IASA and it’s available.

As I stated here in 2006, there is a 4 dB ambiguity at 16 kHz.

Many things conspire to make this 4 dB ambiguity essentially meaningless in a generally low-fi medium. The only reason I’m mentioning this now is that I’ve been bombarded with email from more than one participant in this discussion and apparently there may be some editorial judgment attached to what is posted.

Jay McKnight has graciously permitted my posting of his comments to me:

The problem, I think, is that people now-a-days are used to measuring digital equipment with digital measuring equipment, and think that precision measurements are always possible. As you well know, THIS JUST AIN’T SO WITH AN ANALOG MAGNETIC TAPE RECORDER! We try hard, and often come close, but there are just a lot of complicating factors, and most engineers are not aware of them.

For instance, there has NEVER been a measurement standard for tape flux vs frequency (“frequency response”) in ANY format. I have published on it (link here), but when we approached the IEC committee way back when, they said “we don’t write measurement standards like that”, which I think really meant “don’t confuse me with facts, my mind is already made up”.

There is also a problem revealed in the excessive spacing loss document, here . We suspect that this is the cause of the discrepancy in the wavelength-response  of the Philips cassette calibration tapes, but they would never admit that. Note that the German Open Reel calibration tapes even at the higher speeds 15 in/s (380 mm/s) also show this problem.

Note also that the AES Standard for measuring the medium-wavelength fluxivity ( AES Standard AES7-2000 (r2005): AES standard for the preservation and restoration of audio recording — Method of measuring recorded fluxivity of magnetic sound records at medium wavelengths (Revision of AES7-1982)) does not exist as an IEC standard, and we think that the amplitude of the medium-wavelength fluxivity on the German Open Reel calibration tapes at the higher speeds are about 10 % in error (link here).

When we approached BASF with these problems on their Calibration Tapes circa 1978, they said something to the effect “Your measurements are probably right, but we’ve been doing it this way for years, and we’re not going to change it now.”

So between the technical problems and the political problems with the IEC Committee (which, to a great extent WAS Philips and BASF), plus the fact that this is OBSOLETE technology, I think that trying to solve the problem with a 4 dB error at a 3 um wavelength on a cassette tape is futile. Take it for what it is. If it sounds bad, fix it as best you can.

To this, I might add that a colleague (and former member of the Ampex Standard Tape Lab) who would prefer not to be mentioned by name (and I can understand why after this week’s barrage of emails) has noted in at least some high-end cassettes back in the 1980s and 1990s that, if put away in storage for a year, they would lose substantial amounts of high-end. Some might have lost close to 10 dB at 10 kHz.

This high-frequency loss due to aging has never been studied, but it is one potential explanation for the very poor Dolby tracking with older tapes.

The same colleague also noted that in his measurement of cassette calibration tapes all of them were hot at the high end. The ones prior to the Prague Compromise were hotter than the ones after, but all were hotter than what the standard states.

A hot calibration tape will cause the repro EQ to be turned down. Adjusting record EQ to match playback EQ will mean that the tapes recorded on a machine calibrated with a hot calibration tape will be hot. Tapes recorded on machines that meet the standard will play back sounding dull on machines calibrated with the hot calibration tapes.

Please note, according to  IASA TC04 IEC Type I tape reached its final equalization curve in 1974, and that was 3180/120 µs, and the change was in the low end from 1590 to 3180 µs. IEC Type II and IV tape reached their final equalization in 1970, and that was 3180/70 µs.

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

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.

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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.

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.

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 was getting rather frustrated and since it was a four-track tape and one of the techniques that is supposed to reduce squeal is to play the tape faster, I dragged out my Racal Store 4DS instrumentation recorder which has a 75,000 Hz bandwidth at 15 in/s and played it at 15 in/s and digitized it at 88,200 samples per second. After slowing it down 4x and ending up with a 10 kHz bandwidth (which I subsequently truncated to 5 kHz since there was no useful information above that, but lots of noise–same as the non-squealing portion of the real-time transfers on a Studer A810).

Why did it work? — That is the big question. I suspect lower tape tensions than even the reduced-tension settings on the A810 and different head geometry were major factors, plus overall shorter unsupported tape spans, and few stationary objects contacting the heads, but there was still an erase and record head which had been removed from the A810. I think that the 4x speedup helped greatly.  I also turned up the outside air (how I cool the studio in the winter–I like my fresh air this way–in the summer, of course, it’s connected to the central air conditioner) which kept the tape and recorder cool. I also think that the Racal Store 4DS doesn’t heat the tape and head assembly as much as most pro audio recorders do.

I received great support and wonderful ideas on both the Ampex and Studer mailing lists. Special thanks are due Jay McKnight who has been a supporter of speeding up the tape to eliminate squeal (which is really stick-slip and causes frequency modulation of the audio). I had avoided the 4x speedup on the A810 because of the signal electronics bandwidth limitations. While in this case, 20 kHz would work fine, I wanted to digitize with 40 kHz bandwidth to make sure I wasn’t losing any highs.

There may be room for misunderstanding as to the precise topology of the Racal Store 4DS tape path. Here is a brief explanation. The tape comes off the top of the supply reel and around the top-mounted tension sensor which is a roller. The tape then is unsupported from that roller until it enters the head area. The large diameter device at the top of the head area is merely a tape guide. It is both a “face” and “edge” guide both in and out and does not rotate. Next the tape passes the erase and record heads on the left side. The heads are on the outside facing the centre. Then the tape turns 180 degrees around the capstan motor’s soft capstan. The capstan also drives the mechanical footage counter. As the tape heads up, it passes the reproduce head and then encounters the tape guide on the other side. It then goes over the tension roller at the top and onto the takeup reel. The reel servos are interesting as they are fast and can drive the tape in either direction. This is useful since there is no pinch roller. The photo below shows a closeup of the head area.

As an aside: you can infer from the above picture that the complement of tape machines in my studio changes. The Studer A810s in the background are being set up to record full-track mono archival reels of some cassettes.

Before running out and purchasing one of these machines, please read this post:
http://richardhess.com/notes/2008/01/09/using-the-proper-toolsand-dont-try-this-at-home/

For several years, we have been discussing the differences between Sticky Shed Syndrome (SSS) and Loss of Lubricant (LoL). It appears from my latest research (presented at the 2006 Audio Engineering Society’s 121st Convention in San Francisco in October) that LoL does not really factor into the equation for most tapes and that an overarching failure mode is Soft Binder Syndrome, or SBS. Sticky Shed Syndrome appears to be a subset of SBS.

The classic recommendation for tapes suffering from SSS is to bake them and, for now, the continued recommendation is to bake tapes for which baking works. These include:
Agfa (pre-1990): PEM 468, PEM 469
Ampex/Quantegy (1970s-1980s): 406, 407, 456, 457
Note: Recent reports indicate that these problems may exist in tapes made in the 1990s
and later, even under the Quantegy name.
Audiotape/Capitol (early 1980s): Q15
Note: This tape may or may not respond to baking. Some tests will be conducted soon.
Scotch/3M: 226, 227, 806, 807, 808, 809
Scotch 250 has also exhibited some tendency towards SSS

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

Baking (or incubation) times are getting longer, and 12 hours is not uncommon for 1/4-inch wide tapes. Some tapes need to be re-baked after partial unwinding due to centre-of-reel increased inter-layer pressures. There is some discussion of pressures and tensions here.
If these are squealing and leaving significant deposits, they should be baked (at your own risk). The now-expired Ampex patent for baking tapes can be found here. Almost all SSS tapes are back-coated tapes and the interaction between the magnetic coating and the back coating may be part of the problem.

Tapes which squeal (and generally leave less of a deposit and are generally not back coated) appear to be suffering from SBS. SBS appears to be a change in the glass transition temperature of the magnetic coating. The glass transition temperature (Tg) is the point where the plastic turns from smooth to rubbery. If the Tg falls below the temperature of the head (slightly above room temperature due to friction and player heat dissipation) then the tape is likely to squeal. Small deposits of magnetic coating on the head or other fixed surfaces will exacerbate the squealing. Of course, the drop in Tg is not an isolated phenomenon, but rather a symptom of serious binder degradation.
Lowering the temperature of the playback environment will permit successful playback of some tapes suffering from SBS. We currently have a dedicated refrigerator with both a reel and cassette machine inside. Others have reported success in using an outside balcony during cool/dry weather.

Baking a tape that generally exhibits SBS (and not SSS) may exacerbate the condition and it is not recommended to bake suspected SBS tapes.

Tapes which appear to be suffering from SBS include:
Scotch/3M: 175 and Melody 169 (a seconds brand of Scotch)
Sony: PR-150
Pyral: (type numbers unknown for this French tape)

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

We have seen cassette tapes also suffering from SBS. These were generally made from pancakes and the tape type is unknown.
As an alternate, you might try Marie O’Connell’s tried and true method shown here. In this case, it appears that the isopropyl alcohol is acting both as a lubricant and as a coolant, and may be also acting as a solvent to remove or inhibit deposits from the tape onto the fixed surfaces.

We know that the sealed can will accelerate the vinegar syndrome degradation. The big question is are these tapes an anomaly or the mine canary for some (or all) acetate tapes?

The composite photo below shows some of the conditions that we found. Note especially the rolled outer strands showing extreme shrinkage from vinegar syndrome.

Click for a larger image.

We were able to transfer these tapes,   but the sound quality suffered due to the unsteadiness of the tape transport. The quality of the sound was due mostly to the fact that this was recorded at 30 in/s (probably 77 cm/s) with a full-track head. Nothing beats areal density for robustness.

I recently came across a 3-inch reel of acetate tape, not in its original box, that showed the following pattern in the box. This tape was recorded in Fall of 1964 and the photo was taken on October 2006, 42 years later. The tape played well, considering it was originally recorded at 1.88 (1-7/8) in/s.

All of the outgassed material that was absorbed by the cardboard was no longer free to degrade the tape.

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

Fellow restorer Doug Pomeroy sent me a photocopy of Herman Burstein’s “Tape Guide” article from the May 1977 issue of “Audio” magazine. Robert Coe of Manchester, CT, wrote in saying “…some of these [Scotch 175] tapes have developed a high frequency chatter or squeal which is mechanical and can be stopped by rubbing the tape with a light coating of talcum powder. The squeal only occurs on the Scotch 175 tape even when used with several different brands of tape machine.” Burstein replied, “Yes, I’ve heard other complaints about squeal, sometimes involving Scotch tape which is not surprising in view of 3M’s large share of the market, but yours is the first complaint about 175 tape.” He went on to say that another 3M tape exhibited this but it was limited to the batch and 3M replaced it.

We do not recommend the talcum powder approach as it overall has proven to be a bad idea since it gums up the machines and increases spacing loss more than other solutions.

Doug is currently having a joyous bout with 175 but Art Shifrin apparently has a proprietary mechanical fix to the tape deck that allows playing 3M 175.

We are researching more about 175 and hope to have updates. The use of decamethylcyclopentasiloxane (D5 or cyclomethicone) has had mixed results with 175 and Sony PR-150, another known squealer.

There are many possible causes for this adhesion (or pinning, as it is sometimes called). For this tape, we believe moisture intrusion and poor storage conditions contributed to the problem. It is often a problem with plastic leader tape.

Slow unwinding has reportedly helped, as has cold, dry storage for an extended period.

This tape   (Melody 169) also squealed, but we finally got an acceptable transfer. Fortunately, this was recorded on only one track, and it wasn’t the one with all the holes in this picture.