Corey Bailey

           Audio Engineering

USEFUL INFORMATION

BAKING ANALOG AND DIGITAL AUDIO TAPE (OR NOT) Disclaimer: Neither I or my company has profited in any way from the people or organizations mentioned in this article. This would include the links at the end of this article. The opinions expressed herein are mine alone and do not reflect upon the people or organizations mentioned in this article. Preface:  First of all, I want to be very clear: In this article, I am only talking about polyester base audio tape. This would exclude all acetate base audio tape. Acetate base audio tape will not benefit from the processes described in this article. In fact, you can do harm or permanent damage to acetate base audio tape by heating it in any manor. A considerable amount has already been published on this subject and one can find a wealth of information available on the internet simply by plugging the title of this article into your favorite search engine. There are several research papers that require membership in specific organizations in order to gain access. This, obviously, can become quite expensive. However, there is a wealth of information that is public information. There are links at the end of this article to some in-depth reading on the subject for those who wish to delve into the science. I would like to thank all of those who reviewed this document before it was posted. Some background: A surprising number of well respected people, whom have authored articles, are making the assumption that audio tape can be successfully baked without any consequences. I tend to disagree and will only bake audio tape (Analog or Digital) as a last resort because changes in the oxide take place that are both measurable and often permanent. To be fair, there are certain brands and types of analog audio tape that will only respond to baking and there are a few that simply won’t respond to any of the processes listed in this article. I will first test a polyester (PET) based tape for playability. If I have found any evidence of Sticky Shed Syndrome during the initial testing phase, I will then decide (Based on years of experience) if lubrication or baking is best. I have found that my method of lubrication, coupled with the type of lubricant that I use, is about 90% effective. That said, there are those instances where the only solution to making a tape suffering from “Sticky Shed Syndrome” playable, is to bake it. Sticky Shed Syndrome is actually the result of a chemical process known to scientists as “Binder Hydrolysis”. The process of baking analog audio tape was first proposed by AMPEX Corp. in the late 1980’s. The process was patented by AMPEX (Patent #5,236,790). The recording industry (Film, Records, etc.) was quick to adopt the process described in the AMPEX patent because everyone involved had experienced the problem of degrading audio tape. To my knowledge, AMPEX has never pursued anyone for patent infringement.   Binder Hydrolysis: About 80% of all polyester base analog tape manufactured from the 1970’s through the turn of the 21 st  century will suffer from some form of binder hydrolysis. The problem worsens as time marches on. The type and severity of binder hydrolysis is as varied as the different types of tapes themselves. The most common indication of the problem is an unusual amount of oxide buildup on all of the stationary parts of a tape transport. Tapes suffering from binder hydrolysis will often “squeal” while playing. Another indication is the tendency of the oxide layer to stick to the stationary parts of the tape transport while the tape is at rest but threaded up, ready to play. Some tape transports will be unable to go into play mode if the stiction problem is bad enough. Severe cases will have the layers of tape adhering to each other causing the oxide from one layer to stick to the backside of an adjacent layer. Successive baking may have detrimental effects. Those of us who have baked a tape more than once, and then transferred it, have heard a type of audible degradation that we cannot adequately define. There has been very little research on the downside of baking analog and digital audio tape. Most of the early research on tape degradation was done on data tapes, mainly because that is where the funding came from. One result of the earliest research was to store the tape at very low temperatures and low humidity.  Apparently, Hydrolysis reactions (Sticky Shed Syndrome) can actually be reversed, if the Relative Humidity is below 24 percent and the temperature is below 65° Fahrenheit. In 1995, at the fourth Joint technical Symposium (JTS), a research paper was submitted by Kevin Bradley of the National Library of Australia. The research paper was titled: “Anomalies in the Treatment of Hydrolyzed Tapes.” What caught my attention about this paper was that the research was carried out on 1/4” analog audio tapes using test equipment designed to analyze the same. What was discovered is that when baking audio tape above 50°C (122° Fahrenheit), there was a measurable increase in the dropout rate and a slight frequency loss (1/2dB above 10kHz). The high frequency loss increased slightly as the temperature was increased. Both trade-offs can be acceptable when baking is the only way to recover the audio signal. In 2015, Goran Finnberg of The Mastering Room AB, posted to the Association of Recorded Sound Collections (ARSC) Listserv that he had measured increases in the AM (Amplitude Modulation) distortion starting with the first baking cycle and increasing with each subsequent baking of the same tape. Goran, to my knowledge, has yet to publish a peer reviewed paper on his findings so, for now, his research will have to be considered anecdotal. However, his findings tend to bear out what myself and many other audio engineers have experienced when transferring an audio tape that has been baked. The vast majority of procedures and processes involved with the recovery of the information contained in degrading media is from the personal experiences of those mired deep in the problem and is therefore anecdotal. Although a few of us have pulled back the curtain to take a deeper look at the problem, very little scientific research has been done as to the possible effects of those anecdotal processes, either short or long term. Some of which have become industry standard! While I’m sure that the engineers at AMPEX Corp. observed the scientific process when doing their research on baking, there is no mention in the patent of possible chemical alteration or side effects. In fact, mention is made in the patent that the baking process may indeed stabilize the tape being baked. A situation that has since proven to be just the opposite.  An alternative to baking is offered by Charles Richardson. He is perhaps the only person to have conducted actual laboratory research on Sticky Shed since the 1980's. According to his journal papers, his work which was performed by independent forensic chemists, discovered several previously unrealized factors, including: (1.) That the carbon black back coating is the primary cause of hydrolysis in modern tapes, though oxide binders can also suffer hydrolysis due to poor formulations. (2.) How and why back-coating hydrolysis affects the oxide layers. (3.) He defined the damaging chemical effects of exposure to elevated heat levels based on well established knowledge of chemical behavior. Mr. Richardson subsequently developed a no-heat process to remove the backing material from both the back of the tape and the residue from the oxide as well. I personally know of two people who have had their Sticky Shed tapes treated with this process and the problem has apparently disappeared. One person had this process done by Mr. Richardson more than five years ago and his tapes are still stable. Charles Richardson claims that tapes he restored in 2006 not only remain stable, but are sonically superior to any other treatment. So, Mr. Richardson may indeed be onto something. Currently, he is not offering his process of removing the back coating as a sale or service. However, Mr. Richardson is busy getting the word out to various professional organizations so, we’ll see. There is a link to his website at the end of this article. That said, I have encountered Sticky Shed Syndrome (SSS) on non-backcoated tapes as well, although the situation is rare as non-backcoated audio tape tends to be vary stable. Some European manufactures also back-coated their audio tape products but instead of using a carbon based coating, they used a plastic material consisting of very fine plastic particles. I have encountered SSS on some of these tapes as well. One set, in fact, couldn’t be saved, no matter what we tried. Fortunately, the owner had another source for the audio. Assessing a polyester base reel of tape for Binder Hydrolysis: The first thing I do with 7" reels (and smaller) is to insert a pencil into spindle hole and un-thread several layers by hand. This will tell you if the layers have the tendency to stick together. If you are dealing with a 10-1/2" (NAB Hub) reel, you will most likely have to mount the reel on the tape deck. Hopefully, the reel brakes on the tape deck will be disengaged, allowing for easy un-spooling of the tape. Carefully un-spool several layers by hand, and observe how the tape comes off the reel. The problem, if it exists, may not show itself on the first few wraps. The tape should un-spool effortlessly without the layers wanting to stick together. If you are concerned about the tape being on the floor, use a clean empty bucket or wastebasket to catch the tape as you un-spool it.  If you do have to mount the reel on your tape deck, you can use the other reel to take up the slack. When I check NAB reels on a tape deck, I will thread the tape directly from one reel to the other, avoiding the rest of the transport entirely.  Use both hands to rotate the reels. Once you have convinced yourself that layer-to-layer adhesion is not a problem for the first few wraps, backwind the tape to the supply reel and attach about 4 feet of leader to the head end of the tape. The type of leader (Paper or Plastic) is a matter of individual preference. Leader has several benefits: It allows for thread- up and run-up to speed on a professional transport before the beginning of the tape to be transferred passes across the play head. Consumer decks tend to have shorter tape paths and many were quite good at recording modulation to the very end of the tape. Leader also keeps the end of the tape protected at the outer edge of the reel and protects the tape from the unevenness of slotted hubs at the center of the reel. Eventually, leader will be applied to both ends of the tape. Having leader at both ends of the tape allows for the transfer of the entire tape, end-to-end. Know that sometimes layer-to-layer adhesion won’t rear it’s ugly head until you are at the last few wraps near the end of the supply reel. This problem most often occurs on reels with smaller center hubs (5” Reels, 7” Reels, etc.) So, this is why you need to pay attention to how the tape comes off of the supply reel until the very end. If, you suspect that layer-to-layer adhesion is present, STOP and consult a professional. Solving the layer-to-layer adhesion can be tricky and remediation is best done by someone who knows how to deal with the problem. Often, baking (done properly) is the answer. If any of the oxide has come off and stuck to the back of the adjacent layer, it's “game over” for that section of audio tape. Once leader is attached to the outer edge of the tape, with the tape threaded up, play into the tape for about 30 seconds. Stop the tape deck and disable the transport (As though you are going to edit the tape). Pull the tape away from the transport and observe all of the stationary parts of the transport (heads, guides, idler arms, etc.). There should be NO evidence of oxide build-up on any of the stationary components. Then, with the tape deck is in STOP mode and the tape threaded up, rotate the reels back and forth by hand. There should be no resistance. No tendency for the tape to stick to any of the stationary parts of the tape path. Pull the tape away from the transport and clean everything. I use denatured alcohol. Inspect the Q-Tips or cloth that you used for any oxide residue. Presuming that you have a very clean tape path, play the tape for about 30 seconds again. While the tape plays, observe how it comes off the supply reel. There should be no tendency for the tape to stick to an adjacent layer. Listen to the tape while it is playing past the heads (put your ear up close to the head stack). There should be no squealing or any suspicious sounds of any kind. Stop after 30 seconds or so, pull the tape away from the transport and inspect all of the stationary surfaces (heads, guides, idler arms, etc.) for any sign of oxide deposit. Clean the entire tape path again and yes, inspect the Q-Tips or cloth that you used for any oxide. With the tape threaded up, ready to play, rotate the reels back and forth by hand in between each “play test” to check for any signs of stiction. By now, you have played about a minute or more of the tape and should not have observed anything out of the ordinary. It is at this point that I will back-wind* the tape to the beginning and lubricate the entire length of the tape. When I have finished with the lubricating process, I will attach a leader to the end of the tape and I am ready to begin the transfer after a rigorous cleaning and inspection of the entire tape path. I will often transfer side B first to avoid the unnecessary rewinding of the tape even though, on my particular tape deck, the tape only comes in contact with ball bearing surfaces for any operation other than playing the tape. *The tape deck that I use for this process (An Otari MTR-15) has been modified so that the tape itself only comes in contact with rotating bearing surfaces in any mode other than play. Even the tape lifters have been sleeved so that the sleeves act as rotating bearings. I will only use the Fast-Forward/Rewind functions to position the tape prior to transfer. Fast-Forward and Rewind functions are accomplished using "shuttle" mode with the tape threaded around a reversing idler, away from any stationary parts of the transport. Know that some tape decks, such as the Studer 80 series, are designed with only rotating bearing surfaces that come in contact with the tape for all operating modes. There are some things that you can do that will help things: 1) Cover the Erase and Record heads on your tape deck with Teflon tape (Fig. 1). This is relatively easy and there is a link to Teflon tape at the end of this article. ONLY use wooden or plastic tools for attaching and removing the tape. Metal tools run the risk of damaging the heads.                           Fig. 1     Showing Teflon tape covering the     Erase and Record heads. 2) Sleeve the lifters so that the sleeves act as bearings. This is not so easy to do and has operational consequences so you may want to skip this procedure. If you do add sleeves to the lifters, know that full speed rewind or fast-forwarding is OUT. With sleeves over the lifters, only slow movement of the tape with the lifters engaged is recommended. Mainly use the Fast-Forward and Rewind buttons for positioning the tape prior to transfer. Otherwise, use alternate modes for shuttling the tape. Without sleeves over the lifters, know that every time the lifters are engaged, you are scraping the valuable oxide with a stationary object! And now, for the baking process: So, consider the baking of analog and digital audio tape as a last resort because the end result may be somewhat compromised. If you are at all unsure about what to do, consult an experienced professional. If you do have to resort to baking, the advice from the experts (myself included) is to properly bake a tape and then transfer it to the digital domain as soon as possible. Mainly because the stabilization effect offered by baking is only temporary, lasting a week or two at best. AMPEX Corp. recommended baking at a temperature of 54°C. (129-130°F.) I prefer to use a lower temperature of 48°C. (118°F.). This usually requires a longer baking time so I will usually let 4 or 5 reels of 1/4” tape go 24 hours before checking them. For fewer reels, I will check the tape after about 12 hours. For a single reel, 8 hours is the check point. I use a dehydrator and a digital thermometer that will reach the tape itself for checking actual temperature. National Public Radio (NPR) has over 155,000 analog tapes and a special laboratory oven, where they bake 1/4” reel-to-reel tapes at a temperature of approximately 51°C or 125°F for about 8 hours. The industry standard for the feature film companies is to bake their 1/4” reels at between 120-130°F. for 8 to 12 hours. (Longer when necessary) For wider tapes, the baking time is simply adjusted to allow for the width and number of tapes being baked at once. While I have personally witnessed the use of temperatures higher than 54°C. or 130°F., I certainly don’t recommend it. At higher temperatures, you are running the risk of permanent damage. Think: “Lower and slower.” The cooling process. Once your tapes have completed the baking process, they have to be cooled to room temperature. Plan ahead for the removal and acclimation process. Use cotton gardening gloves (at least) for handling the hot reels. Have a safe space ready to receive those hot reels that is in or the same temperature and humidity as your transfer facility. Since I use a dehydrator for baking and generally acclimate the tapes overnight, I will often transport the dehydrator into the studio and let the tapes cool and acclimate inside the dehydrator. Room Temperature may be an ambiguous reference but the bottom line is that the tapes, once baked, need to be at the same temperature and humidity as your transfer facility, whatever that environment is. The time it takes to acclimate to your work environment will vary. Some facilities are climate controlled, some are not. For those that are not, seasonal variations will play a large role. One factor is the amount of tapes that have been baked. I will only process the amount of tapes that I can comfortably transfer in one day. My studio is in Southern California (The arid Southwest). Acclimation time for the amount of tapes that I can transfer in one day is usually 3 to 4 hours. However, I will usually plan things so that the tapes have overnight to acclimate to the studio room.   Many companies with large holdings will “Bake first, ask questions later.” Manly because it’s simply the most cost effective way to migrate their large inventories of analog product to the digital domain. That said, these same companies employ knowledgeable people who know how to properly assess the product. Like NPR, these companies have extensive transfer facilities and still are playing “catch up.” Adding to the problem of degrading analog tape is that digital audio tape is showing signs of SSS. This is something that those of us working in the trenches never expected because the manufacturing process for analog audio and digital audio tape is completely different. The digital audio formats that have exhibited problems (so far) are: DA88, DAT and reel-to-reel digital.  DA88’s and DAT’s are particular problems because both are cassette based and, being rotary head formats, can ruin your expensive playback deck while you figure out the problem. There are some video tape formats that are degrading as well. Those being: Hi-8, Digital 8, 3/4” analog and some 1/2” professional digital formats. In general, if you are to consider baking digital audio or video tape, use my recommended temperatures for analog audio tape as a starting point (48°C., 118°F.) or slightly lower temperatures and longer baking times if you want to be extra safe. The reason for the extra caution is because both the base film and the oxide layer are much thinner than analog tape. Adding to the problem is that many of the digital audio (and video) formats are in cassettes so the results are really variable. I have noted about a 50% success rate when baking cassette based formats. Reel-to-reel digital is much better. So, in the end, there is no good news here. As I point out at the home page of this website: “Not only is magnetic media degrading, but the equipment and expertise needed to retrieve those aging recordings is becoming increasingly more difficult to find.”  Some Links: Charles Richardson’fs website: http://www.rezerex.com/ From Josephson Engineering (Microphones): http://www.josephson.com/bake_tape.html The Library of Congress: http://www.loc.gov/preservation/scientists/projects/sticky_shed.html

Magnetic Media Preservation, Library of Congress:

https://www.loc.gov/preservation/care/magbib.html

Storing and handling of magnetic media CLIR: https://www.clir.org/pubs/reports/pub54/5premature_degrade/ Teflon tape: https://www.mcmaster.com/#tape-(made-with-teflon-ptfe)/=1bcy6ti Return to TOP of page © Corey Bailey Audio Engineering

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