Audio Digitization

Table of contents

  1. Pre-digitization conservation treatments
    1. Triage and Inspection
      1. Audiocassette
      2. Open Reel
      3. Grooved Disc
      4. Cylinder
    2. Cleaning
    3. Incubation
    4. Tools for conservation
  2. Set-up and monitoring during transfer
    1. Machine set-up
      1. Audiocassette
      2. Open Reel
      3. Grooved Disc
      4. Cylinder
    2. Initial playback
  3. Post-digitization editing, spot-checking, and packaging

Pre-digitization conservation treatments

Triage and Inspection

Audiocassette

Before any other kind of evaluation occurs, there are a few mechanical manipulations that will need to be performed on all audiocassettes:

  • Remove the record tabs located in each corner of the top of the cassette shell.
  • Due to long-term storage conditions, cassette shells may be warped slightly. To remedy, squeeze the shell gently by applying pressure with your forefingers and thumbs to the pair of holes located at the center of the cassette.

Next, fast wind the tape backwards and forwards, keeping an eye out for any problems that may arise. If the tape gets stuck in the transport, the issue could be:

The interlock tab on the hub has broken due to age and the leader has broken free from the hub.

  • This problem is quite common with certain runs of TDK cassettes. The solution is to open the shell in order to get inside the housing. Most cassette shells are held together with five very small Philips Head screws.
  • Remove the screws and carefully separate the top part of the shell from the bottom.
  • Remove the lubrication pad, and find the broken interlock piece that will be visible; dispose of it.
  • Disassemble a stock Maxell cassette to retrieve a complete hub with leader tape. It is strongly suggested that you replace the hub with attached leader from the stock cassette rather than trying to interlock the new hub to the existing leader tape.
  • To remove the leader from the audio tape, you will need to swab alcohol onto the splicing tape. Once the glue has loosened, use a dull razor blade to GENTLY remove the splicing tape from both cassette housings.
  • Reattach the new hub and leader to the tape that needs to be preserved, using the proper width splicing tape in a cassette editing block. Keep in mind: the splicing tape will need to be attached to the back side of the tape and leader. (Hint: The back side is shiny; the oxide side is dull. The oxide side faces outward.)
  • Reassemble the entire assembly and fast forward the tape to the end, paying attention to the way the tape is looped through the cassette shell path (the tape should be moving around the posts located at both bottom corners). If you are not sure how it is looped, open up a sealed one from stock to make sure.
  • If the take-up hub is broken, it is likely that the supply hub will probably exhibit the same problem. Be prepared to open up the assembly again when you get to the end. If you need the second hub, just remove the tape from the second hub of the Maxell cassette you’d previously opened for parts.
  • General suggestion: keep a box that holds 10 cassettes for spare parts, such as lubrication pads, pressure pads, shells, screws and hubs with leader attached.

The splicing tape that joins the recording tape to the leader tape has dried out and is not adhering anymore.

  • This will be apparent when you see the take-up hub spinning by itself, and by examining the bottom window of the cassette shell and observing that there is no tape in its path. You will have to go through most of the procedures outlined above in order to remedy this problem. However, you won’t need to replace any parts; just cleaning the leader and audio tape of dried up glue and re-splicing the two with new splicing tape. Of course, when you wind the tape to the end, the splice at that point will also come apart. Be prepared to disassemble the shell a second time.

If the tape starts to wind but slowly comes to a stop without advancing to the end of a side, the issue could be:

The cassette shell has warped and is applying too much pressure to the tape and hub.

  • If after squeezing the shell gently the cassette still refuses to move the tape easily, you will need to replace the shell. Use one of the stock Maxell shells. Make sure that you remove the record tabs as outlined above, as well as putting a piece of Scotch Tape across the top end for each side so that the new shell mimics the configuration of the original shell regarding what type cassette it is. Tascam decks have an automatic sensor concerning that determination. Older cassettes are Type I – low bias setting. The Maxell shells are for Type II playback – high bias setting.

The lubrication pads have dried out.

  • The lubrication pads are located between the hubs of tape and the top and bottom portion of each shell case half. It is a good rule to replace them at the same time that you are replacing the outer shell case housing. Using the ones found in the Maxell cases will correct the problem.

The tape may be exhibiting signs of Sticky Shed Syndrome (SSS), a condition in which the lubricant embedded on the oxide side has broken down due to moisture absorption.

  • There are certain brands of tape that will exhibit this problem, most notably Ampex (456, 20/20, or Grand Master Series), certain batches of AGFA, or obscure non-branded tapes created them for mass duplication (generally these items will have no indication of manufacturer either on the shell or label).

Another set of problems commonly encountered when working with cassettes from various manufacturers is the design and construction of the tape’s shell and pressure pads.

Many older cassette assemblies are “welded” together and have no screws to hold them in place.

  • This is very common with cassette brands such as Scotch Highlander/Dynarange, or cheaper budget brands like Irish, Shamrock and Certron. If the shell has to be opened, then there is a simple procedure to excise the tape hubs from the assembly: First, wind the tape, if it all possible, to the start. Remove the record protect tab in the upper left or right side that corresponds to the reel hub that has no tape on it. With a small to medium flathead screwdriver, insert it into the record tab slot and push down hard until you see and hear the plastic shell start to separate. (You may want to put on a pair of protection goggles when you do this.) As it starts to separate, move the screwdriver blade towards the center of the assembly in order to break the seal between both halves. Proceed to the other end, making sure you don’t insert the screwdriver too far in, otherwise you may damage the full hub of tape on that side.
  • Once you have separated both halves, carefully remove the two hubs and place them into a completely new shell assembly. Be careful to note the tape path as you do this; always make sure that the tape goes around the tape posts that are just adjacent to each tape guide wheel located at the lower corners.

Some cassette assemblies will be held together with screws but may have pressure pads that have fallen off or have completely deteriorated.

  • In this case, the shell must be opened, the lubrication pad removed, and the original pressure pad discarded. A replacement pad assembly can be taken from stock Maxell cassettes. Some of the older cassette assemblies contain an older style pressure pad assembly that can be entirely removed and replaced with the one that is contained in the Maxell shell, by replacing the inside metal plate along with the pressure pad that is affixed to a metal strip. Note how it is placed in the Maxell assembly; this must be duplicated when inserted into the shell you are working with.

Open Reel

Determining the tape stock (acetate or polyester)

  • A bit of history: If you are dealing with tapes that are marked as being recorded in the 1950s through the mid-to-late 1960s, chances are the stock will be of an acetate type backing. This formulation, which was the standard until the 1970s is now very unstable and has a multitude of problems associated with it, especially reels that have been exposed to environments where there was excessive heat and humidity during long term storage. THESE TAPES ARE THE FIRST TO BE CONSERVED AND THEN PRESERVED…
  • The fastest way to determine the base material of a tape is to look at the container and see if there is any formulation/type number on its description in the labelling. Most will say acetate or possibly “plastic” as the base or backing material.
  • To make sure, remove the reel from its box and place it in front of a strong lamp or bulb. If it is acetate, you will see a certain amount of light shine through the tape while viewing it; this is also known as being translucent. Mylar/polyester tape, introduced in the very late 1950s, is a much more robust and stable form of tape. When you place it in front of a light, there will be no translucency.

Acetate-based tapes

Assessing the state of the previous wind

  • When dealing with a private collector’s or radio station’s collection of acetate tape, chances are that the tapes were left in a “fast wind” position on the reel in the heads out direction. What does this mean? Essentially, collectors did not want to waste time tight winding a tape back to the beginning (or termed the “head”) of the reel after it had been played. Radio stations often did the same, as tapes were used for quick recording, editing, and playback; once a tape was played, it was fast wound back onto the reel for “bulking” (total erasure with an electromagnet) or slated to be destroyed if the tape had been used too many times.
  • Proper conservation requires that the tape have a library wind, that is, played through the transport at the fastest possible speed, resulting in an even resulting “pack.” Determining the track and speed configuration (described below) will help you figure out which end of the tape should be tight wound.

Vinegar Syndrome

  • Any tape exhibiting vinegar syndrome should be prioritized for reformatting, or considered for de-accessioning from the collection.
  • VS can affect tape on any reel size (10.5-inch, 7-inch, 5-inch, etc.).
  • VS appears most often with triacetate-based audio tape from the 1950s and ‘60s. Most acetate audio tape did not use this base, so this problem is not nearly as widespread as it is in film.
  • VS is primarily associated with Eastman / Kodak or Durol audio tape from the 1960s. If either of these brands is found, they should be inspected immediately. However, any acetate brand that has been stored in a sealed environment (plastic bag, un-vented film can, etc.) may be subject to VS.
  • Often, these reels will be in plastic bags inside the tape boxes. These should be discarded. The cardboard boxes themselves may show absorption of the acetic acid. These boxes, or any other housing that isn’t vented or provides no air-exchange, should be replaced.
  • There is a high-degree of contagion with a VS-infected tape. One VS tape sitting on a library shelf may infect as many as 5-10 other reels surrounding it. These need to be checked and neutralized to varying degrees as well.
  • Any stock exhibiting VS should be removed from general collection storage areas. An infected reel should be rehoused in a vented, acid-free box and put into cold, low-humidity storage. It should NOT be frozen. It should not be sealed in any plastic container.
  • Often, a VS audio tape can be curled, warped, brittle, or otherwise physically compromised. Sometimes they lose the translucency of a normal acetate tape. However, they can sometimes be played and transferred without many problems. The playback machine would need to be thoroughly cleaned afterwards.

Repairing splices and replacing leader

  • To begin, thread the tape (left/supply side) through the transport of the machine and onto the take up reel located on the right side.
  • If the tape has leader attached to it, remove that leader and the splice holding it in place.
  • Clean the edge of the tape using a Q-Tip immersed in either a combination of 99.9% isopropyl alcohol and lighter fluid (heptane), or 190 Proof “Everclear” distilled spirits.
  • Unwind one revolution’s worth of tape off the reel and look for any residual dried glue that might have oozed below the original splice.
  • Once the tape has been threaded properly and the reel tension motors set to the correct tension (Low for 7”, High for 10-12”), engage the play button at the highest speed that the machine will allow. Let the tape play until a splice passes through the tape transport (the splice will likely break as this process unfurls).
  • As performed with the leader, clean the area where the splice has fallen off, as well as the layer of tape above and below the spliced area (Residual glue will be on the backing of the tape below the original splice, as well as on the oxide side of the tape above the splice. A strong light or, better yet, touch with an index finger will help locate any glue that has adhered. Be gentle in cleaning these area, as applying pressure can remove the oxide coating in some formulations.
  • The amount of dried out glue that has spread to adjacent layers will become more noticeable as the tape progresses; this is due to increased pressure near the center hub. Occasionally, dried glue will be visible on both sides of the reel where the original splices had been made. If you are familiar with your playback tape recorder, you can move through a tape more quickly by “rocking” the fast forward and rewind controls back and forth.
  • Make sure that all splices are repaired and new leader tape is replaced, since the original leader can be made of either plastic (which maintains a surface static charge that could magnetize the tape) or paper (which can have a high acid content that prevents the new splicing tape from adhering).
  • In certain instances, a tape may exhibit a form of oxide ripping, where the oxide layer does not adhere any more and starts to stick to the backing of the adjacent layer of tape in sections. This is called “blocking,” for which there is no remedy. All you can do is wind the tape back and reshelf it. A symptom of “ blocking” is a rather “gooey” or sticky feel to the oxide side as you are handling the tape. If you suspect that there is a problem, wipe the oxide side with a Q-Tip immersed in Isopropyl alcohol. If it comes off easily and looks sticky, then you have a tape that has already “blocked;” you’ve saved yourself wasted time and effort in determining that the tape is unplayable.

Determining track and speed configuration

  • Start by winding or rewinding the tape to the middle of the reel. Set the speed of the tape recorder to 7.5 ips and the tape head selector switch to 2-track mode; make sure that the output of both channels is equal and near the SRL of the machine (Note: this set of instructions is for the Otari 5050 B series of decks).
  • Engage the play mode and listen to the signal. If it sounds correct, then the speed is 7.5 ips. If it sounds slow, then the speed is probably 15 ips. If it sounds like “chipmunks,” then it is probably 3.75 ips. Adjust your player to the appropriate speed.
  • After you have determined the speed of the tape, the track configuration can be confirmed. If you are dealing with very early tapes from the 1950s, there are only 4 possible track configurations: half track mono both directions, half track mono one direction, two track double mono one direction and full track mono.
    • Half track mono both directions: When viewing the meters and audio from each channel, you will hear a signal in the forward direction in the left channel and a signal in reverse in the right channel. Both will be of equal amplitude when playing back the tape with the 2 channel head configuration. To confirm that you have a half track recording in both directions, engage the 4 channel head. If the signal stays the same, then you definitely have a half track recording running in both directions.
    • Half track mono one direction only: In this instance, the left channel will only have a signal present in the forward direction. It could also have only a signal in reverse in the right channel.
    • Two track double mono one direction: This format is more common with radio station tapes and mastering studio tapes for production purposes, since it uses the most amount of tape in a shorter span of time. Usually the speeds for this track layout will be either 7.5 or 15 ips. When you engage the tape with the 2 channel head for playback, both channels will be at the same volume level (assuming the original engineer was proficient). When you flip the head assembly to the 4 channel mode, the right channel will drop about 6 dB. This is due to the fact that the right channel of a 4 channel head is playing partially in the guard band area of a 2 track recording where there is no signal; it’s picking up a partial signal from the lower channel of a 2 track recording.
    • Full track mono: As the name implies, there is only a single signal recorded across almost the entire width of the tape in one direction. This mode of recording was used early on for the first consumer tape decks and abandoned shortly thereafter, since it was a rather inefficient way of storing a lot of audio on a reel; half-track recorders replaced them within a short time. This mode was used by radio stations and mastering studios because of fidelity issues and fewer problems concerning speed instability since most recordings done that way were recorded at either 15 or 30 ips. The only difference in observing meter level and audio output, is that when you switch between the 2 track and 4 track heads, there should be no attenuation of the signals at all.
  • There is one other configuration that you will come across if the tapes are of a more recent vintage:
    • Two track stereo one direction: Testing for this configuration is performed the same way as Two track double mono one direction, except there will be a stereo signal from the two channels. When you switch from the 2 track head to the 4 track head, the loss of volume in the right channel will be approximately 6 dB.

Procedure for properly tight winding acetate-based tapes

  • If the original reel is 7” in diameter, a replacement reel that has no slots near the center should be employed. If it is a 10-1/2” reel, then the center hub can be replaced with a NAB hub that is also slotless. The invention of the slot on reel-to-reel tape reels was for convenience of threading; for long term storage, it was and is a disaster for acetate-based tapes since it causes severe deformation of the tape that was wound near the center of the reel. A library or tight wind has to be performed, with what is called a “B” or oxide-out configuration; this is achieved by putting a half twist into the tape after it has past the pinch roller and capstan motor; this is done so that the resultant “cupping” or curling of the surface of the tape is reversed. This procedure will ensure a better head-to-tape contact point during playback.

  • Determining the track configuration will dictate the direction in which the tape should be wound:

    • If the tape is recorded half track mono in both directions, it should be wound onto the new reel such that the beginning of the second side is wound onto the new reel. As a result, the finished tape would then be ready to play at the beginning of side one when it needed to be transferred. Tack down the leader tape with a piece of red adhesive tack down tape on the flange which corresponds to side one; this way it indicates to the operator which side has to be up when playing back this specific reel.
    • If the configuration is either full track mono, two track double mono, half track mono one channel only, or two track stereo one direction, the tape should be wound onto the new reel starting with the beginning of the tape. When it has finished winding, tack down the leader tape with a piece of blue tack down tape on the top flange. This indicates the tails out position for the next operator handling the tape. The older and more deformed the tape is upon inspection, the longer it will have to sit on the shelf in order to repair the inherent damage. The minimum amount of time could be 6 weeks to as long as 3 months for any sort of improvement in shape before it will play back properly.

Mylar/polyester-based tapes

  • This brand of tape became popular in the late 1950s and was a major source of recorded audio in the both broadcast industry and consumer applications. The difference between polyester-backed tape and acetate is that its basic formulation is much more stable and robust than its acetate-based equivalent. Even if it is left fast wound for years, it will tight wind without any problem. To test to see if you have a reel of this formulation, check the box for any brand name and formulation listed; if not present, shine the reel up to the light–it is not translucent, and therefore, no light will come through. The methods for cleaning splices and replacing leader tape are the same as described above for acetate-based tapes. Tight winding does not have to be oxide out, since there is no edge damage or cupping present.

Additional track and speed configurations

  • In addition to the previously mentioned track configurations, mylar tapes have an additional set of track options that became popular during this period:
    • Quarter track mono 4 directions: A favorite among collectors because it utilizes an incredible amount of space to record a lot of audio. Essentially, there are four discrete signal tracks on this type of reel. Side one has tracks 1 & 3, and side two has tracks 4 & 2. As before, wind the tape to the center, and start playing it with the 2 track head, with both channels on. If you hear audio coming out of both channels forwards and backwards, switch the playback assembly to the 4 track head; you will then hear two separate and discrete signals from each channel. This is a quarter track mono 4 direction tape.
    • Quarter track stereo 2 directions: In this situation, a stereo signal is recorded on the tape utilizing tracks 1 & 3 on side one and tracks 4 & 2 on side two. As above, start playing the tape with the 2 track head. You should hear pretty much the same results as quarter track mono 4 directions, except you may hear some stereo separation this time. Using the 4 track head once again, you will now hear whatever program is on side one in stereo without any interfering signal from the second side. This is a quarter track stereo 2 directions tape.
    • Quarter track double mono 2 directions: Same as quarter track stereo 2 directions except the same signal is recorded in both channels on both sides of the tape.
    • Quarter track single mono 2 directions: In this case, the mono signal is recorded only on track 1 for side one and track 4 for side 2. To determine if you have a quarter track recording, play both channels on the recorder with the 2 track head. You should hear the left channel playing back a correct signal and the right channel should be playing a signal that is going backwards. If you shift the playback assembly to the 4 track head, the right channel should disappear. If it does not, then you have a half track mono both directions tape.
    • Quarter track single mono 2 directions: This one is a bit tricky. Essentially, you will have only one signal on one of the tape. The only way to tell if it is four track or half track is to turn the tape over and play the reverse side with both heads. If you hear the single track coming in backwards with both heads, then it is a half track mono recording. If the signal disappears with the 4 track head, then it is a quarter track recording.

Procedure for properly tight winding Mylar/polyester-based tapes

  • Conservation of polyester-based tapes is similar to the process outlined above, with one key difference: the tape does not need to be wound oxide out. Track configurations should again determine the way in which a tape should be tight wound and taped down. T

Grooved Disc

The AMI Labs will be primarily called upon to digitize NYPL’s collection of transcription discs, which can be divided into the following categories:

  • Shellac pressings
  • Shellac/Vinyl compound pressings (a.k.a. “Victrolac”)
  • Vinyl pressings
  • Aluminum or glass-based lacquer-coated discs (“acetates”)

Shellac, Victrolac, and Vinyl

TBD

Lacquer Discs

Lacquer-coated discs made their first appearance in the United States in mid-1934 and became the main medium of instantaneous recordings until the mid 1950s, when superseded by reel-to-reel tape. These discs were originally made from an aluminum base that was sprayed or dipped into a liquid cellulose acetate compound. During WWII, due to the shortage of aluminum, the base was changed to glass. The aluminum base used for the manufacture of these discs did not resume until mid to late 1944.

This medium was originally intended to be a temporary way of recording audio events quickly and efficiently, for the purposes of playing back the event immediately for copying, audition, or rebroadcast. Since the base of the disc and the lacquer coating have slightly different coefficients of temperature, that is, slightly different rates of expansion or contraction due to changes in temperature, there is a great risk of the lacquer surface delaminating. This can be accelerated by poor temperature/humidity conditions as well as damage due to extended contact with water. While the aluminum-based lacquers are fairly resilient when being handled, the glass-based discs are EXTREMELY FRAGILE for obvious reasons; this is only exacerbated by the fact that at the end of the manufacturing period of these discs, the glass core was made extremely thin.

Upon inspection of any disc, the original envelopes and sleeves used for storage should be checked for stability and integrity.

Cylinder

Throughout the various curatorial divisions at NYPL, there are approximately 3,000 audio cylinders dating back to the 1890s. These range from commercial releases to home recordings to the famed Mapleson Collection of Metropolitan Opera recordings. The AMI Labs have the capability to transfer, digitize, and digitally restore a large portion of these 3,000 cylinders via the Archeophone playback machine. [IASA TC-04],(https://www.iasa-web.org/tc04/audio-preservation){:target=”_blank”} Guidelines on the Production and Preservation of Digital Audio Objects, contains a wealth of useful information regarding best practices for cylinder handling and playback. Note: the Archeophone should only be operated (or supervised) by an experienced engineer due to the complexity of the machine and the potential to damage a source if not set up properly.

The Mapelson Cylinders

The Mapleson cylinders, along with several hundred others in our possession, are “brown wax” cylinders, mostly manufactured by Edison. These are made not of wax, but of a metallic soap composite which could be recorded on, and then shaved off if desired and reused. As with many of our brown waxes, the Maplesons are of varying thicknesses; some are dangerously thin to the point of breakage. These recordings are not only noisy but also fragile and worn from repeated plays. The Mapleson collection should be considered apart from the balance of NYPL cylinders and treated with special care.

Physical Inspection and Handling

Brown wax cylinders are particularly subject to changes in temperature rather than humidity. Moving these cylinders to a different environment should be a gradual process, preferably using an insulated cooler over the course of several days to slowly acclimatize the cylinders to the new room temp. Sudden changes can result in the cylinders weakening and shattering under the slightest pressure. This has been observed and reported by Dr. Eric Monroe at the Library of Congress (Uncovering the Nature of Damage to Early Wax Cylinder Audio Recordings during Storage, 2018).

Cellulose cylinders are much more durable and resistant to damage than the earlier waxes. They were often manufactured in various colors to denote specific genres. These cylinders usually contained a plaster core, so they are also subject to humidity and temperature changes. They should be properly stored in stable, low-humidity environments in approved archival cases.

The Library of Congress recommends handling cylinders in the following ways:

  • Hold with middle and index fingers, open to a V shape, in the cylinder
  • Do not touch the outer, grooved surface (the playing surface) of the cylinder
  • Allow wax cylinders from cool storage to acclimate to room temperature before touching to avoid thermal shock

Prior to playback, physical inspection of the cylinders is required in order to avoid damage and other problems during transfer. A careful examination of the surface, preferably under the digital microscope, will help to discern any problems or foreign matter on the playing surface (cracks, chips, dirt, mold, fungus, metal salts, etc.). In most cases, debris can be removed with a dry, lint-free cloth or brush. No solvents or water should be used.

Cleaning

Audiocassette

Open Reel

Grooved Disc (Keith Monks cleaning machines)

General operating instructions

A detailed Owner’s Manual and Instructions for Use for the Keith Monks Record cleaning machines can be found in the AMI Preservation Team Drive, but several other steps may be needed to ensure optimal operation:

  • Always check to see that the water in the waste jar is at a level BELOW the bottom of the plastic tubing that is attached to the through connector inside the jar. If the level is getting too high, empty the waste jar immediately. At the same time, make sure the thread has come through the plastic tubing and is sitting freely immersed in the water. If the thread has gotten caught in the line, you will have to pull it out through the vacuum arm via the nozzle, possibly cut off the end if it has become unraveled, and reinsert it through the tubing with the vacuum on. You may have to loosen the tightening nut that holds the spool of thread underneath in order to measure out the proper amount of string that should be in the jar; it is usually about 2 inches past the end of the tubing.
  • Check the level of the fresh water jar. If it needs replacing, do so. If you use the Disc Doctor solution, it is a ratio of 10 parts water to 1 part DDS; Photoflo 200 is about 2 capfuls of it vs. a filled jar.
  • Generally, you will go through approximately 2 full jars of fresh water to one jar of waste water before you have to empty out the waste jar. Periodically check the level of the waste jar; if it fills up faster than what was said above, then change it more frequently. You don’t want that water getting sucked up into the vacuum pump by accident; this will affect the long term performance of that motor as well as cause the rubber gasket to dry out prematurely. There is another problem with the water level going higher than it should – there is a chance that the nylon string can get sucked into the vacuum motor as well, which could damage certain vital parts of it, which would result in a complete replacement.
  • Before you turn it on and place a disc on the platter, move the platter back and forth a little. If there seems to be too much of a free give in moving it back and forth, get a long flat blade screwdriver, and tighten the 2 adjustment screws under the platter that are attached to the bose of the shaft of the motor.
  • Always make sure that there is plenty of water coming through the brush when you wet a disc. A dry brush can scratch the surface very easily.
  • The amount of liquid to distilled water (usually an ounce of detergent to the jar full of water) should be enough to create an even surface tension when applied, such that the water does not disperse when the disc is spinning and being vacuumed.
  • If you are applying the water solution to the disc via the brush and the brush does not make contact with the disc, remove the disc and loosen the two adjustment screws under the turntable platter to raise the entire assembly so that proper contact will be obtained once again. DO NOT force the moveable brush block assembly down onto the disc; you’ll bend the pole it slides on, resulting in it not being straight and it could possible crack, causing a leak.
  • Make sure you have enough towels to capture the water that accumulates on the hood and in the bottom of the dust cover when it is open. Always mop up whatever liquid is present before shutting down for the day.
  • This machine can work for approximately 12 hours continuously before the vacuum motor will shut down. Make sure that you switch to the mode that you are using at the time, and do not keep it in the vacuum mode the entire time you are using the machine.
  • If you lose suction, refer to the manual, which provides step-by-step troubleshooting instructions.

Format-specific considerations

  • Lacquer-coated discs should be cleaned and then preserved within a short period of time.
  • Vinyl discs have a tendency to accumulate a high degree of static charge on their surfaces due to the accumulation of dust and dirt.

Incubation

Audiocassette

The entire assembly must be desiccated in a convection oven, set to a temperature of around 50 degrees Celsius (132 degrees Fahrenheit) for a period of 2-3 hours. The external thermometer inserted into the top of the oven will serve as a guide regarding temperature control. Each control should already be set to the appropriate temperature and variance; only the timing knob will need to be adjusted to the number of hours that the oven needs to be on.

Place the cassettes on the reel-to-reel NAB hubs that are supplied on the bottom shelf under the oven. Make sure that each cassette has a properly affixed catalogue number. After the oven shuts off, let the compartment cool down for about an hour before removing the tapes. When the thermometer reads about 30 degrees Celsius, the tapes can be removed.

Open Reel

Black backcoated Mylar/polyester-based tapes: Starting in the mid 1970s a number of the major tape manufacturers added a carbon-based backing to their tape products that was intended to reduce print-through problems that occurred when the signal was recorded at a high level in order to reduce background noise levels. Unfortunately, quite a number of the formulations that were manufactured at this time exhibited a form of binder hydrolysis which resulted in the lubricant that was mixed into the solution to make the finished product break down due to absorption of moisture from the air. The result is a problem whereby the tape will only play or can be fast forwarded for a short period of time before the transport will stop, and a sticky buildup will be on every part of the tape transport.

These tapes need to be dessicated or baked for several hours. The most effective temperature is between 125-135 degrees Fahrenheit for a period of 4 to 12 hours, depending on the size of the reel and the number of reels that are heated in the convection oven. After they are treated, a period of at least an hour is needed to let the tapes cool before they are handled. Of course, leader tape and splices may need to be replaced after this kind of heat treatment. The tape may also require a cleaning pass with a piece of Pellon cloth to pick up any shedding that may occur before proper playback; of course, every one of these tapes may leave a residue on the transport. Therefore, the transport must be kept clean after each playback, using cotton swabs immersed in 99% Isopropyl alcohol. Keep in mind that this treatment is most effective within the first week; plan accordingly on what you can preserve within that time, once a batch of these tapes are backed. Dessication over the weekend is not advised.

Tools for conservation

TBD

Set-up and monitoring during transfer

Machine set-up

Audiocassette

Always remember to perform a series of checks on the cassette deck before inserting a tape:

  • Clean the transport with a cotton swab and the denatured alcohol. This includes the capstan motor shaft and the erase as well as the record/playback head. Be careful to not apply any alcohol to the pinch roller.
  • Clean the pinch roller with a cotton swab and the rubber cleaner by gently applying the cleaner to the roller while rotating it several times. Use a clean swab to dry the roller after you’ve cleaned it. This will be easier to do if you remove the cover on the door of the machine; it will come off by pulling up on it gently.
  • Demagnetize the heads with the demagnetizer. Remember to turn off the machine before applying the demagnetizer to the heads.
  • Power up the machine, push the switch that opens the cassette door, and insert the cassette to the A side. Close the door and fast forward the tape to the end. After it stops, rewind to the beginning. This procedure serves two purposes: (1) to re-tension the tape in order to remove any deformation due to poor winding and long term storage; and (2) to reduce the presence of print-through issues also resulting from improper long term storage.

Open Reel

TBD

Grooved Disc

  • The disc must be played back on a proper archival turntable that can accommodate a disc that is 16” in diameter. If the arm is too short, the outer grooves could be damaged during playback. The arm should also be adjustable concerning its height in order to accommodate the various thicknesses of pressings in the collection. During playback, the angle of the tonearm from front to back should be perfectly parallel in relationship to the disc while it is playing.

Styli

  • Shellac/Victrolac/Vinyl: Generally, most of the shellac based discs and “Victrolac” pressings were manufactured in the late 1920s though the early 1940s. This means that the groove geometry is slightly larger than later electrical transcriptions made after WWII. One would need truncated styli that measure between 2.5 mil and 3.5 mil in size that are available in both conical and elliptical shapes. For later vinyl pressings (ca. end of WWII to the early-mid 1950’s), a stylus range of 1.5 mil to 2.5 mil in the same variety of truncated assemblies is preferable. MODERN LP STYLI ASSEMBLIES CANNOT BE USED FOR PLAYBACK OF THIS MATERIAL. DAMAGE COULD BE DONE TO THE GROOVES OF THE DISCS BEING PLAYED BACK IMPROPERLY. The compliance of the cantilevers employed in the stylus assemblies should be able to withstand a tracking force of up to 7 grams for proper playback. There are archival assemblies available that will not fit this criteria since they will only track at weighs of 1.5-2.0 grams which can only be used for playback of LP vinyl discs. Therefore, LP styli assemblies cannot be used.
  • Lacquer-coated: Most lacquer discs were manufactured starting in the mid 1930s through the mid-to-late 1950s. This means that the groove geometry will vary from very coarse (approximately 3.5 to 4.0mil in diameter) to a more moderate coarse size (1.2 to 2.5 mil in diameter); some later lacquers may be cut microgroove, requiring a very narrow stylus in order to play them back (0.5 to 1.5 mil in diameter). One would need truncated styli that measure between 0.5 mil and 4.0 mil in size that are available in both conical and elliptical shapes. MODERN LP STYLI ASSEMBLIES CANNOT BE USED FOR PLAYBACK OF ANY OF THE MATERIAL THAT IS NOT CUT MICROGROOVE. DAMAGE COULD BE DONE TO THE GROOVES OF THE DISCS BEING PLAYED BACK IMPROPERLY. The compliance of the cantilevers employed in the stylus assemblies should be able to withstand a tracking force of up to 7 grams for proper playback. There are archival assemblies available that will not fit this criteria since they will only track at weighs of 1.5-2.0 grams which is can only be used for playback of LP vinyl discs. Therefore, LP styli assemblies cannot be used.

Cylinder

  • Before 1902, cylinders could play at any number of speeds, depending on the manufacturer, which ranged (more or less) from 100-160 rpm. Brown waxes were normally played at about 120 rpm. Henri Lioret’s early cellulose cylinders originally ran at about 100 rpm (see Lioret page). In 1902, with the creation of the Edison Gold-Moulded Cylinder (“black wax”) for commercial releases, the format was standardized at 160 rpm at 100 tpi (threads per inch) for a 2-minute playing time or 200 tpi for the later Amberol (cellulose nitrate) cylinders for a 4-minute playing time. These same specs generally hold true for Columbia and other brands. The Archeophone provides for exact speed reproduction as well as fine tuning to adjust for pitch.

  • The groove on a cylinder is not like that on an LP or on most 78s. Cylinders have a vertical-cut groove, rather than a lateral cut. Therefore, either the pickup is rewired, or (more conveniently) the signal coming into the DAW is phase reversed and fine-tuned in mono to ensure the most phase-coherent response from the Archeophone. The signal is then recorded in discrete left & right channels using a stereo pickup, rather than a mono one, as often times, one groove wall will have less wear than the other. These are kept as discrete channels for the Preservation Master.

Styli

  • When choosing the proper stylus, always play the test cylinder in stereo AND mono and compare. We have many cartridges and stylus sizes and shapes here at the Audio Labs, not only for discs but also for cylinders. Stanton, Shure, and Ortofon cartridges along with custom-sized styli from 0.5 - 10 mils are in our toolbox. The cleaner and quieter, the better. IASA TC-04 states:

    • 5.2.4.3 Selection of a suitable stylus in vertical recordings is governed by different criteria to lateral recordings. Rather than choosing a stylus to sit in a particular space on the side of a groove wall, playback of cylinders and other vertical cut recordings requires that a stylus be chosen that is a best match for the bottom of the groove. This is critical with instantaneous cylinders, where even very light tracking forces will cause damage if the incorrect stylus is chosen. A spherical stylus is generally preferred especially if the surface is damaged, though an elliptical stylus may well avoid frequency dependent tracking error. Typical sizes are between 230 (9 mil) and 300 µm (11.8 mil) for standard cylinders (100 grooves/inch) and between 115 (4.5 mil) and 150 µm (5.9 mil) for 200 grooves/inch cylinders. Cylinders should be replayed with a stylus whose tip has a radius a little smaller than the bottom radius of the groove. A truncated stylus will damage the groove because tracking will take place at the edge rather than the tip, resulting in increased pressure to that part of the groove.

  • In many cases, these stylus sizes may be too big, especially for brown waxes. Therefore, starting with a 2.6 mil elliptical and then going smaller may help.

  • WARNING: FOR BROWN WAX CYLINDERS, WHEN PLAYING BACK, BE MINDFUL AT ALL TIMES OF POTENTIAL GROOVE DAMAGE DUE TO IMPROPER STYLUS SIZE, SHAPE, ANGLE, TRACKING FORCE, OR ANY COMBINATION OF THESE!! THE DAMAGE IS PERMANENT!!

Initial playback

Audiocassette

  • Begin playback with the Dolby circuit turned off. Pan the monitoring mixing board to mono. Using a rubber handled torque driver, adjust the screw located to the left of the playback head, turning it slightly clockwise or counter clockwise until you hear the “sweet spot” where high frequencies are most prominent. This can be confirmed on the digital oscilloscope. If it is a true mono signal, the resultant image will be an almost perfect lissajous pattern in which there is no spreading of the signal (a perfect or close-to-perfect straight line). If the signal is in stereo, then you will have to adjust according to your hearing.
  • Set the output level of the tape deck to avoid overloading both the input of the A/D converter and the output of the cassette deck itself. Both machines have red peak indicators that will come on if the signal is too high. Also note: the output of the cassette deck is at unity gain when the volume control is set to 8.
  • If the content being digitized is music, use the KORG Auto tuner to determine whether the cassette is running at proper speed. If this is not the case, turn on the variable pitch control and move the potentiometer in either direction until the recording is proper pitched. When playing back spoken word material, start without any speed correction.
  • If the speed seems off, record a small section of audio and load it into a program that will provide a graphic display of the signal; at this point you will be able to see whether there is any hum in the recording. Try approximations using the pitch control, re-recording and reviewing the same section of material. It is always better to try to get things right in the analogue domain first; the pre-emphasis curves on the tape were set by the original speed of the tape. If it takes too long to perform this task, the resultant preservation file could be resampled later when a service copy/edited master is created.
  • Assume that most early cassettes (1969-1971) were recorded without Dolby B encoding. Things become more complicated during and after 1972, when Dolby capabilities were added to many cassette decks. Always look for any annotation on the cassette that would indicate the presence of Dolby encoding but, if lacking, use your best judgment and trust your ears (while erring on the side leaving the signal unadulterated). Some general notes about Dolby, especially pertinent for tapes recorded from the late 1970s through the 1990s:
    • If you find a tape that sounds very noisy and seems to have “pumping” distortion (that is, unusual lower frequencies that become louder in in high volume sections), then the chances are it has been encoded. Once enabling the Dolby circuit, the problems discussed should disappear.
    • If, however, there is no pumping distortion and it sounds moderately “hissy”, you probably have a recording that has not been encoded. The proof is when you enable the circuit, the resultant signal will be rather muffled and would sound very dull.
    • One last caveat: as cassette tapes age, especially the normal bias tape formulations (Type 1, 120 microseconds) there is a tendency for upper end frequencies to diminish over time. Even though these tapes may be marked as encoded, it could sound much clearer to leave the Dolby B playback circuit disabled. When in doubt, do not employ noise reduction as it significantly affects the upper frequencies.

Open Reel

TBD

Grooved Disc

Playback EQ

  • From the dawn of electrical recordings (ca. 1925), a set of record/compensation curves have been employed when cutting a disc that must be reversed upon playback. Each record manufacturer came up with its own record/playback curves which then were modified over the years. As a result, an archival phono preamp is needed to replicate these playback curves properly. There are but a few preamps available that can function in such a manner. One is made by TimeStep in England, which has separate controls for bass and treble playback for this type of material. Another is KAB Electronics in N.J. who has come up with a similar preamp unit that has set playback curves that are in combination with one another. One of the requirements is to create a STEREO SIGNAL UNPROCCESSED WITH THE PROPER PLAYBACK CURVE APPLIED DURING PLAYBACK. Since 1955, NAB established a standardized playback curve for the reproduction of the modern LP; it is known as the standard RIAA curve for LP playback. This circuit became the standard in all modern analogue audio equipment when a phono cartridge was employed.
  • Before running trials concerning the playback of a pressing, one needs to run one simple test. While the disc is turning, play part of the inside grooves and take note of any noticeable “swaying” from side to side of the tonearm head. If that problem cannot be resolved by readjusting the disc on the turntable after the turntable is stopped and restarted, that disc cannot be transferred properly and should be returned to the Library for a more detailed restoration. If there is too much lateral swaying during playback, a noticeable pitch instability in the signal known as “wow” will result.
  • There are a number of references available to guide to engineer through this part of the restoration. On the Web, this site contains useful information regarding the playback curves of pre-RIAA discs.
  • When monitoring the signal in order to determine the proper stylus assembly and playback curve, make sure that your monitoring system is panned to mono. This will give you a more accurate aural picture of the disc you are playing back, since it will cancel out the vertical noise or rumble that is present in the stereo playback of a monaural as well as the “stereo” groove noise effect that can be present. As a result of listening in mono, some of the transient noise (clicks, crackle, etc.) will be minimized as a result of out-of-phase noise cancellation.
  • You can use the Powell guides in determining the proper playback curve of the disc you are about to transfer, OR you can use a “house default” curve of 400 Hz turnover / -12 dB at 10kHz rolloff. In determining the proper playback stylus, one can produce a signal that is relatively quiet without any “scratching” noises from using too wide or narrow a stylus; from experience, your hearing and judgment will tell the difference.
  • Another factor to consider is to get a playback that has the least amount of tracing distortion. This anomaly is usually a non-linearity in the upper frequencies where the resultant signal sounds worn, fuzzy and/or rather unpleasant in loud passages. Experience will guide you after a while.

Cylinder

  • Archeophone set-up is perhaps the most crucial part of the cylinder preservation process. As stated previously, the Archeophone can be quite complex to set up for a beginner on their own. Even a technician with experience on this machine can require at least a half-hour to properly set it up prior to transfer. Suffice to say, such a technician needs to be consulted for Archeophone playback.
  • Parameters include (but are not limited to) machine level, platform height and level, tonearm angle and level, tracking force, evenness and truing of cylinder rotation (especially if the cylinder is warped), securing of the mandrel, etc. Any one of these parameters incorrectly set could damage the cylinder. Anti-skate is generally not a factor as it is in disc playback since the tonearm is on a worm screw mechanism.

Post-digitization editing, spot-checking, and packaging

TBD