ANALOG TAPE

Corey Bailey

Audio Engineering

USEFUL INFORMATION ANALOG TAPE: DO IT YOURSELF?

60 years ago or so, it was easy to spot a die-hard audiophile because he or she owned a reel-to-reel tape recorder. I was one of them. I owned an early production-model Roberts, which was considered to be one of the serious audiophile decks of its day. Although the manufacturers tried to make home recorders as simple as possible, the whole process had a rather steep learning curve. It’s even steeper today. Record collecting can be relatively simple, particularly if a person sticks to vinyl LP’s (which, will make the selection of a record turntable a lot simpler). However, one can purchase a single turntable which will play all speeds and sizes of records. Analog tape recorders are mostly format-specific. Tapes recorded on different format recorders are generally not interchangeable. For example: In order to be able to play 98 percent of the ¼” tape formats that were used, I own (and have to maintain) four tape decks. This brings up the maintenance issue: Tape recorders are very complicated electro-mechanical pieces of equipment for which very few (if any) parts are still available. This also means acquiring the proper test equipment and learning how to use it. If you want to try this yourself at the hobby level, the most difficult task will be finding an affordable, working reel-to- reel tape recorder to get started with. There are some talented technicians that specialize in restoring old professional tape decks for archival purposes. As you might imagine, these refurbished tape decks cost professional prices. The alternatives are consumer and ‘Prosumer’ reel-to-reel tape decks. Some have been expertly refurbished and good used ones can still be found. For those who are new to analog audio tape recording, here is a link to a student primer provided by the University of California, Santa Cruz titled: Analog Tape Recorders. Check out the Analog Tape page in my glossaries section for some simple definitions and descriptions. Also visit my Links page. Some of the sites there have volumes of information about playing and archiving audio tape. You will need to learn how to identify the various formats, adjust parameters such as azimuth, and be able to get the best out of decaying tapes that have been improperly stored for years. I’m not intentionally trying to discourage you from becoming a collector of audio tapes, I’m simply telling it like it is and suggesting that you do some extensive research before jumping into a hobby that can easily turn into a money pit. One of the most popular uses for home reel-to-reel recorders was to make song tapes of favorite songs from records or off-air. I made a few myself way back when. This is the vast majority of what you are going to come across at garage sales and swap meets. Some are OK, some are poorly made. Of course, a lot of family history was recorded on reel-to-reel tapes, and this is what you may find in Grandma's attic. On the other hand, there were quite a few commercial recordings made for reel-to-reel enthusiasts, and some still survive. Some are very collectible! Acetate base tape The vast majority of family history recordings on reel-to-reel tapes that I have archived were made from the middle 1950’s through the 1960’s. This was the era of acetate tapes that are now very brittle and delicate. This type of tape is prone to breaking and leaving jagged ends that are difficult, if not impossible, to repair. Acetate tape can be identified by holding the reel up to a bright light. If you can see light through the reel, it’s most likely acetate because the acetate base is clear. Fig. 1 is a 7” reel of acetate tape being held up to a 40 watt light. The light transmission properties are obvious. Polyester tape, (Fig 2.) when held up to light, is opaque. (The light on the surface of the reel is the camera flash.) The one caveat here is that if the acetate tape in question is suffering from a deformity called ‘cupping,’ it may not pass light edgewise as well as shown in the example. Cupping is when the edges of the tape curl up somewhat, making the tape resistant to wrapping on a reel. The tape itself looks like the shape of a metal Venetian blind. Cupping results from the tape losing moisture over time. If severe enough, cupping can cause the oxide to fall off the backing. You will usually notice the oxide flaking condition on the outer wraps of the reel. While making acetate tape easier to identify because the clear base is now identifiable, flaking is non- reversible. If any of the recording has separated from the base, it’s gone forever, turned into a small pile of oxide flakes. If the Cupping condition is not severe, there is a possible treatment that can be done called a “B-Wind” whereby the tape is wound onto a take-up reel with the oxide out. The tape reel is stored for a period of time to possibly reverse the condition. Acetate tape that has become too brittle to be playable can sometimes be re- hydrated. The short story is that acetate tape usually can be re-hydrated if left in a moist environment. This can be as simple as placing some dampened (not wet) cotton balls in the corners of the tape box with the tape for 24 hours or so, or as complex as making up a system which suspends the tape over distilled water in a closed environment and left for a period of time. The key is to not have the tape come in contact with the source of the moisture. I have written a separate article on this subject which goes into more detail: Moisturizing Acetate Tape. If you have old tape you suspect is brittle acetate, consult a professional or do some research before attempting anything. The information is out there. Polyester base tape Polyester base audio tape first appeared on the market in the early 1950’s, and, by the late 1960’s, it had basically replaced acetate tape. Polyester base audio tape was readily embraced by the professional audio community because the improved oxide formulations allowed for increased dynamic range. Unfortunately, during the mid 1970’s, many manufacturers changed their oxide formulation (mainly the binder and lubrication chemistry), and things started to go bad from there. Some of those newer tape formulations had severe oxide shedding problems. As it turns out, that was an indication of things to come in later years. A surprisingly large percentage of polyester tape that was made in the last 40 years or so, suffers from a condition known as binder hydrolysis. This is a condition whereby the binder (used to adhere the oxide formulation to the polyester base) has absorbed moisture over time, causing the oxide to become soft and sticky and leave oxide deposits on all of the stationary tape recorder parts (Guides, Heads, Tape Lifters, etc.). Quite often, the tape will chatter across the tape heads as the result of a condition known as sticky-shed syndrome. Ampex Corporation, one of the manufacturers plagued by the reformulation problems, came up with the solution of ‘baking’ audio tapes at 130 degrees Fahrenheit for 12 to 24 hours, depending on the size of the reel and the thickness of the tape. Much has been written about this process, and the research continues. Baking is a temporary solution because after a week or so at room temperature, the problem tapes will return to their sticky state. Experience has shown that polyester tape can be baked more than once. The possibility of adverse affects resulting from audio tape baking is still being debated. I discuss the baking process in a separate article. Identifying the track format One of the simplest ways to identify the track format of a recorded tape is to view it with a magnetic viewer. This is a gadget that has extremely fine magnetic particles suspended in a fluid. When placed over a recorded tape, the magnetic viewer shows the actual magnetic recording and reveals the track format….almost. Here are two pictures of recorded tapes revealing their format under a magnetic viewer: Fig. 3 (Right) is a 2 track stereo recording. However, it could be a half-track mono (recorded both directions), since the two formats share almost the same track width and placement (0.01” difference). If the picture above is a half-track mono, one channel will play forward and one channel will will play backwards, when played on a 2 track machine. Quarter track can be recorded in both directions. If that is the case, you will see four bands of magnetism. That would mean it could also be a four channel recording which, shares the same quarter track widths and spacing. At least, by viewing the tape with a magnetic viewer, you can tell which play head format to use for continuing the investigation. If the quarter track tape shows four bands of magnetism, you will have to play it one direction and then turn it over and check the other direction on a quarter track tape deck. If the tape plays correctly in both directions, it’s a quarter track recorded in both directions. If one of the directions plays backwards, you’ve probably got a four channel tape on your hands and will need a four channel tape deck to play it. A quarter track tape recorded in both directions (most likely stereo), played on a 4 channel tape deck will play both forwards and backwards at the same time. Likewise, a quarter track tape recorded in both directions and played on a 2 track tape deck will play both forwards and backwards at the same time with one channel being lower in level if your machine is calibrated correctly. Tape Thickness Audio tape thickness is basically determined by the material used as the base. The actual measurement is of the overall thickness. The oxide and the back coating (if used) are very thin. The measurement itself is in one-thousandths of an inch and is expressed in mils. All acetate back tape is 1-½ mils thick. All professional tape is 1-½ mils thick. Polyester backed tape comes in three thickness; 1-½ mil (also expressed as 1.5 mil), 1 mil and ½ mil which, is often expressed as .5 mil. The thinner tapes may give a better head wrap, but that’s about it. The downside of using a thinner tape is that there is more of the possibility of crosstalk between the layers. Particularly, if the tape does not have a back coating. Lubricating audio tape I will lubricate a tape suffering from binder hydrolysis or sticky shed syndrome first because I consider baking to be a last resort. I have found that the method and product that I use for lubricating polyester base audio tape to be about 90% effective. If the oxide appears to be sticky or shedding during the lubricating process, resists you in any way, stop and read my articles on baking or lubricating audio tape to possibly determine if you should proceed. There are several approaches, using a number of products and chemicals currently in use to lubricate audio tapes. I use a lubricant specifically formulated for audio tape manufactured by LAST Factory. Check out their website. They make products for records and tapes along with information on how to use them. I often have to use more lubricant on problem tapes than recommended by LAST Factory. As you may have guessed, I have a custom built setup that I use for this process. However, you can simply wet a cotton Texwipe® or any lint free cloth with the lubricant and apply it to the oxide while rewinding or forwarding the tape very slowly. By slowly I mean roughly 5–15 inches per second. You can play the tape as a convenient way to move it at a constant speed while applying the lubricant however, I would recommend threading the tape directly from reel-to-reel. If you do play the tape, I would recommend applying the lubricant on the incoming side of the tape before it comes in contact with the heads and I would also recommend covering the heads with Teflon® tape. Teflon tape is very slippery and will protect the valuable oxide, plus it avoids unnecessary head wear. While applying the lubricant, Use an eye dropper to keep the cloth wet. The kit from Last Factory usually comes with applicators so try them to see if they work better for you. Stop as often as necessary to re-fold the cloth and wet it again. The lubricant does evaporate quickly from the oxide however, I have not encountered any adverse effects from the layers winding onto the take-up reel before the lubricant has evaporated completely. While I don’t drench the tape, I do make sure that the coverage is such that the oxide gets wet. Because I’m coming in direct contact with the fluid, I wear rubber gloves or disposable food handling gloves for the application process even though I have been personally assured by the manufacturer that all of their products are safe to handle. I’ve used Last Factory’s tape preservative on all types of polyester base audio tape and acetate base magnetic film as well with good results. I do not recommend lubricating acetate base audio tape although the manufacturer says it’s OK. Magnetic film (16MM, 35MM etc.) is different in that the acetate base is several times thicker than audio tape and so is the oxide coating. LAST Factory claims that treating magnetic media with their lubricant will increase shelf life. I have only anecdotal evidence to support this, but I can say that I’ve noticed no adverse effects on my own tapes after about twenty years of storage. I have recently added an article dedicated to lubricating audio tape. Baking Polyester Tape First, I will only bake a tape as a last resort when no other restoration method is applicable. I use a food dehydrator. It can be that simple. The dehydrator I use regulates the temperature by manually adjusting the air flow through the unit. It’s a simple dehydrator which has no temperature gauge. To make sure that things are at the correct temperature, I use a very accurate digital thermometer with a long probe that allows me to monitor the temperature at the tape reel. I typically use a constant temperature of 118 - 120 degrees Fahrenheit (48 - 49 degrees Celsius) or less. You can be within 5 degrees or so and be fine. At 120 degrees, the baking time will be 8 to 12 hours for ¼” tape. If you want to be safe, operate on the low side and bake the tape longer. I’ve baked tapes around 115 degrees Fahrenheit for 24- 48 hours and longer with great results. Avoid temperatures exceeding 130 degrees Fahrenheit (54.5 degrees Celsius) because you will risk damaging the tape. I have also written an article dedicated to baking audio tape. Important Know that not all brands or types of polyester audio tape will respond to the baking process. Make absolutely sure of the type of tape you have. Research it well before trying anything. Whatever type or brand of oven you use, it has to be temperature stable within a few degrees. Because the air temperature and humidity are ever changing, (time of day, time of year), I run my dehydrator for several hours while monitoring the temperature at the area where the tape is to be placed before I begin the process of baking any tapes. Any oven used for the purpose of baking magnetic tape should not be used for anything else. It should go without saying that a food dehydrator should not be used both for food and magnetic tape. Always, always seek advice from a professional before trying anything for the first time. Transferring Reel-to-Reel Audio Tapes I’m not sure how to describe a process that takes years of experience. Getting the best possible transfer is much more complicated than just threading up the tape and pressing the Play button. I would start by doing lots of due diligence (a legal term). Do the research and learn everything that you can. There are some articles on this site that will help. Audio Cassettes While there are several formats, the Compact Cassette is the most common. The word ‘cassette’ is a French word meaning: “little box.” The technology was originally designed for dictation machines and the format was monaural or ‘mono’ which could be recorded in both directions. Compact cassettes became a consumer format in the early 1970’s and the format was stereo that could also be recorded in both directions. The tape itself is poorly supported which, in most machines, causes skewing that leads to azimuth and wow and flutter problems. Many cassette machines run at slightly different speeds making for compatibility problems. You will find that many audio cassettes have been recorded with peaks well above the normal recording levels than the tape was designed for. When it comes to transferring cassettes that were recorded in mono or stereo, the main problem is azimuth. I prefer to use a dual capstan machine for the format. A dual capstan machine tends to hold the tape steadier. Some Nakamichi cassette decks have pad lifters which, can also be a bonus. Here is a guide to transferring cassettes which, is a downloadable PDF file: https://tinyurl.com/2p86v7wb The only thing that I would add to the guide is to exercise all audio tapes by shuttling the tape if it’s a reel-to-reel or fast-forwarding and rewinding if it is cassette based, before transferring. Use the shuttle mode if your tape deck has one for reel-to-reel tapes. Some tape decks make tape head or lifter contact in shuttle mode which, is a bad thing. Learn what a cassette in good condition sounds like while fast-forwarding and rewinding and listen while exercising each one. Storing Audio Tape All of your audio tapes, records, and optical media should be stored vertically (on edge). Store all of your magnetic audio recordings in a cool dry place that is away from excessive heat or moisture. (So, how many times have you read that on the label of a flour box?) Well, it’s true. Keep all of your magnetic media in an area where the temperature and humidity are the most stable. Large fluctuations in either will accelerate deterioration. Check with your local librarian or the Internet for information on this subject. Archivists recommend an average temperature of less than 50 degrees Fahrenheit (10 degrees Celsius) and 30 - 40% relative humidity or less. Those ‘ideal’ conditions may be difficult to attain in the average home, but maintaining room temperature at 30 - 40% relative humidity (or less) is possible. This likely leaves out the basement and attic unless one or both have been built to maintain a stable temperature and humidity year round. Storing your magnetic media on the highest shelf in a centrally located closet will probably be the most stable environment in the average home. I live in the desert mountains on the West Coast of the US, where a closet shelf works well and the audio tapes have faired well over the years. Analog tape recording has seen a niche resurgence by artists who prefer the sonic characteristics of analog tape. During the heyday of analog recording, there were a dozen or more manufacturers of tape stock and as many manufacturers of recorders. Today there are only a couple of manufacturers of analog tape left and nobody, that I know of, is making new reel-to-reel recorders. I would be remiss if I didn’t mention again that if you have some old family recordings and you are the least bit unsure about them, please consult a professional before doing anything. You may have only one chance to play them. My advice is always free and their is a ‘Contact Me’ button at the top of all pages. Return to TOP of page © Corey Bailey Audio Engineering