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.

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.

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.

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.

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/

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.

Notice how the complete strips of oxide exist on their own, independent of the clear “leader” to which they previously were attached.

I immediately called the client and informed him that this portion of the tape would not be salvageable. He requested I attempt to salvage as much as possible as it contained many family voices from Europe.

I opened the cassette and it looked intact, except the tape was flaking. The flaking had only just started as he was playing, so we went and pulled off the smaller takeup hub (at the bottom in this picture) and found solid tape.

We know nothing of the storage history of this tape, other than it was sent from Europe about 2004-2005 (this is written in March 2006). The dark spot on the side 2 label has me wondering what befell this tape. Nothing looked overheated or charred inside. The specks on the paper and on the window of the side 2 shell half are pieces of flaking oxide.

We proceeded to unspool the supply side, in some instances, the backing and oxide would come off as two interleaved strands, totally unattached to each other. Of course there is no practical way to re-adhear the oxide to the backing. We kept pulling and pulling and finally found solid oxide. We spliced the two halves together.

Note the pile of tape and oxide strands behind the two spools, and the intermittant nature of the firmly attached binder right to the right of the splice. Also note the small chips of oxide all over the place.

Finally, we re-loaded the tape into a new shell as the old one was too contaiminated with shards of oxide and it was easier than cleaning the old one.

We were able to play this and interspersed with music the client didn’t want, there was a total of ten minutes of family voices that we were able to recover and then clean up in the computer. The tape had not been well recorded, either. One section required a 30 dB boost to normalize the level. Algorithmix Noise Free Pro did an admirable job of reducing the noise. Note in the above photo, the white splicing tape to the left side of the window.

Note, in the above photo, the colour of the pancakes on the hubs appears to shift. The oxide coating is probably dual layer (see notes below) and the brown side attaches to the base film while the black side faces the head. The colour shift in the photo is related to this and the angle of the camera. When handling the pancakes we didn’t see any noticeable damage as one correspondent suggested from heat.

I wonder how many other tapes will behave like this in the years to come. This was the worst I have seen to date. Others have reported similar conditions with some French Kodak tape from the 1960s, and some acetate tapes from the 1950s or 1960s.

Ben Torre emailed me some comments that help put this into perspective:

BASF FeCr and CrO2 tapes were among the best of the day, and the SK/SM housings were marvelous in the days when cassette machines had crappy mechanisms that never allowed for proper tape pack. (other than Nakamichi, of course) [You can see the SM feed arms in the second photo of the opened original cassette.] I’m guessing the one shown is early-mid 1980s vintage based on the label. These were good enough for Mobile Fidelity to use when they were selling 1:1 dupes done on JVC decks. (they used the CrO2 tapes.) They were not cheap. I have one they did of Pink Floyd’s Dark Side Of The Moon, and it sounds impressive for a cassette.

The FeCr tapes were dual-layer, so I wouldn’t be surprised if the two layers of oxide had different rates of expansion and contraction. Put them through enough heat-cool cycles, and you might see this. Only way to tell for sure is to do an accelerated aging test.

[As to the cause,] my money is on heat-cool cycles over a 20 year period. Shoe-box in the attic, or more likely a tape left near a heat source over the years. Not hot enough to melt anything, but hot enough to provide lots of dry heat for a long time. Might even have been from intense sun exposure in a window. Look at that tell-tale discoloration on the top of the label.

Don’t bet on [this being a one-off].

One other I can recall in the mid-70s. Memorex had a ferric cassette tape… I forget the designation… that after repeated plays started exhibiting dropouts. Sure enough, one look at the tape showed that the oxide was breaking off in chips from the mylar base….

I’ve also received several other emails on this post that confirm the dual-layer nature of this type of tape and also reminding me that it is a “Type 3″ tape. Type 3 tapes didn’t stay long in the marketplace and were considered quite fragile at the time.

Comments:

Mikkel Breiler Posted Apr 5, 2006 8:55 PM

This cassette I bet it not newer than 1982. I believe that the FerroChrom name was derived from AGFA patents which BASF utilized after their take over of AGFA in very early 80s to make the best tape available at the time – debate we can if Chrome will stand out as the overall winner, as Chrome tape held up better due to it being a one layer tape and the fact that consumers reluctance to adopt the new TYPE III formula (probably becuase it was competing with TYPE IV) we never saw too much development at the time to get a better tape from the manufacturers who wanted to push the media. But I will vote for Chrome.
The SM mechanism was popular because it worked, most decks back in the day had awful take-up capabilities and the Security Mechanism seemed like a straight forward solution to the problem.
So when AGFA was incorporated into BASF they took a tape type that they hadn’t developed themselves and added their – if I recall only type of mechanism that worked towards an even spooling – SM invention. And I believe were it not for all the diseases the TYPE III tape-infant had to endure the type might have survived longer – but personally either TYPE IV or TYPE III would have eventually won most ground.
I have some one or two AGFA FerroChrom cassettes and I believe two BASF FerroChrom cassettes. And also a Sony 7′’ reel of FrCr-7-550-BL tape, and I have them only for reference because I happen to have decks which allow for selecting such. Neither tapes in my collection display the problem seen here.
And I am surprised that the BASF tape had problems like the one pictured above. But as the patents were developed otuside of their lab this poor tape from BASF may be the results of poor management at lower levels where AGFA engineers and other knowledgable people did not receive enough credit for their pioneering efforts and were not allowed to continue to make even better versions of the TYPE III tape. Or hindered in doing so.

Now for the observed discolouring. I have seen this one several BASF cassettes of the early 80s, with the SM invention. And I must conclude that it is simply poor glue for the labels. This is not something only found with BASF tapes of bygone times, but something several brands have ocasionally exhibited. Though in my collection TDK, Maxell and Sony have never had the issue. I have more pre-recorded cassettes with this problem (and the glue drying out so the labels is loose/missing) than I have BASF or AGFA tapes with poor glue. But it may happen.
Storage is the key, and apparantly the brave little tape you got never stood a chance.

It does strike me as odd when BASF – knowing that the brand covers a lot of factories that produce this or that chemical and – would have enough ties with other companies to come up with better glue for labels than what we see was apparently the case. maybe this is just another anomaly we can chalk up to ‘management success’.

But not every company can draw a winner when several years on, one engineers idea that looked very effective, cost saving, and or which the marketing department found would be useful as a buzzword, became a wrong decision. Hindsight is always 20-20.

So the FerroChrom tape had been out for a few years in its heyday, but when this baby hit the street either BASF was asleep at the factory or just did not bother too much with a slow seller which showed no improvement in the market, and poor storage just got the better of it.

Sincerely
Mikkel Breiler

Tony Amato Posted Mar 23, 2006 7:04 PM

These FeCr dual layer tapes were one of three brand formulations available between 1980 and 1986. Sony, Scotch and BASF were the 3 major players for Type III formulations. Dual layer configuration ~ top coat (layer) of chromimum dioxide over a base coast (layer) of ferric oxide. Great combination when you think of it ~ yet prone to drop outs when to subjected to climatic changes that can occur in an automobile or just general improper storage. Many considered it a low cost alternative to the then expensive Metal Type IV formulations that were emerging.

I still have a cache of Sony FeCr tapes recorded in the early 80’s ~ recordings of the Mobile Fidelity Beatles Collection vinyl. They have mostly survived due to careful storage, but some are now suffering from signal loss and a couple have begun to shed in similar fashion as the one depicted above.

Anyone having critically archived voice or music on tapes of this age, let alone tapes of this formulation, should seriously consider digital transfer before Oxidation and Age catch up and steal the recordings…

Tony

More from Tony on Apr 17, 2006 11:51 AM

With regard to the top of label, centered discoloration ~ It strikes me most obviously as natural oil/soil remnants from handling by a greasy/dirty set of fingers (more than likely build up over time) and then, subsequent aging, oxidation and environmental attack to an already weakened label surface. I’ve seen many a tape label look this way by way of friends who have massive tape collections and not a single sense of how to handle such a delicate product…

B77 Experience Posted Jun 4, 2006 10:29 AM

I recently bought a lot of still sealed BASF CSII from about the same time (a slightly newer model, but still a SM edition, with the large window).

The tape is perfect (typical BASF Chrome, no dropouts, good high frequencies, not too tolerant to hot levels), but the untouched labels exhibit dark spots all over (although they are distributed in a uniform area).
Strange enough, Side 2 is worse than Side 1 on all of the 4 tapes I bought. More glue, perhaps?
So, either a problem with glue or ink.

There are several ways this can happen:

• The erase head can be dirty—this usually leads to high frequencies being erased and lower frequencies still audible
• The erase head can be misaligned—this often provides a partial erasure, but careful use of track selection can find a section of track with less crosstalk.
• A similar problem occurred on quarter-track reels with misaligned record heads where recordings from the opposite direction would invade the tracks for the forward directions. Again, a specially adjustable narrow head usually solves this.
• A completely non-functioning erase system—this is what we suspect happened with the current project. There were no track dissimilarities nor any other way we could find, including looking at the tape with the 8-track cassette recorder to separate the underlying, unwanted recording from the wanted one.
• A totally unrelated mechanism that may sound the same is if the microphone or tape recorder picks up a broadcast or other radiated signal and records that along with the desired signal.

We opted not to proceed with any noise gating as it would not improve the overall audio quality for listening and may actually impede transcrption.

While not a success, we were able to confirm to the client that there was no way that could preserve the fidelity of the desired sound and remove the undesired sound. The desired interview was completely intelligible and could be transcribed. It was just distracting to listen to.