We have recently completed our second audio tape restoration seminar.

We had three great attendees. One of them, Andy Kolovos of the Vermont Folklife Center shared these comments:

I want to thank you again for the workshop. I’m certainly still assimilating stuff in my head, but it was terrific. I learned so much… Through these workshops you’re doing the archival field a huge service. The ability to tap into your experience and take what we learn back into the world with us enriches everyone. Because you are willing to share your knowledge, skill, and passion with those of us who love these audio resources, work with them on a daily basis and are eager to learn all we can about their care, more of the aural heritage of the world will survive into the future. Your generosity is wonderful! Thanks again!

You can see the brochure for our November 2005 seminar here.

Comments from the November 2005 seminar are in the brochure for the May 2006 seminar.

The first three of the four days we were together about 13 hours a day (including dinner at various restaurants) and we didn’t stop talking audio. We covered a LOT of ground and the questions and discussions were great.

There have been rumours that Nakamichi used a different cassette standard than the other manufacturers. This is not really the case. Everyone thought they were using the same 3180/120 or 3180/70 microsecond equalization as specified in IEC Pub 60094-1, 1981.

As I understand the history, both Nakamichi and STL in the late 1970s discovered that when they made calibration tapes based on the published time constants in the standards, their response showed that the then-common BASF alignment tapes were approximately 4 dB high (hot) at 16 kHz.

It is assumed that BASF, who made the calibration test tapes made an error in calibrating their reproduce heads’ response in one of two areas: (more…)

This post has been updated as: http://richardhess.com/notes/2007/03/21/soft-binder-syndrome-and-sticky-shed-syndrome/

For several years, we have been discussing the differences between Sticky Shed Syndrome (SSS) and Loss of Lubricant (LoL).

Recent work in which I’m participating seems to indicate that what we thought was happening in both instances may not be really what is happening.

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

If these are squealing and leaving deposits, they should be baked (at your own risk). The Ampex patent for baking tapes can be found here.

The classic test for determining if a tape is suffering from LoL has been to bake it and see that baking fails. The assumption has then been that it is loss of lubricant. This test, however, may exacerbate the condition and it is not recommended to bake suspected LoL tapes.

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

We have seen cassette tapes also suffering from LoL.

There are several ways to address playing LoL tapes, but, for the moment, we are not prepared to publish anything definitive beyond Marie O’Connell’s tried and true method shown here.

Often a tape comes in for restoration that has been poorly wound or poorly stored. Here is an example:

One of the interesting things about this particular tape was it had been recently wound on a constant-tension professional machine prior to shipping to me.

We think that the entire tape had not been re-wound, allowing the higher tension wind to compress the inner core slightly, causing this cinching. After transferring the tape (which didn’t show much ill effect for its cinching), we still found it difficult to get the tape to wind smoothly on the reel.

Therefore, our current suggestion is if you find a tape like this, do not rewind it and attempt to clear up the cinching unless you are also ready to transfer the tape, as there are no guarantees that it can be wound better after unwinding.

Please see this post for an update (2008-02-15).

While the Ampex Mastering Equalization is well documented on this site and at the MRL site, and standard equalizations are detailed at the MRL site on page 3 of this document, I am always amazed when I discover additional, supported tape equalizations. Certainly there have been proposals for alternate equalizations. Jay McKnight has published a paper (here) about this. This post is about something different.

Teac Corporation, with their X-2000M reel-to-reel tape recorder included a button called “Extra Efficiency” to be used with then-new tapes that had double the coercivity of standard reel-to-reel audio tapes. This changed the recording equalization (and the bias and possibly the reference levels) to better make use of the new tapes to improve the overall sound.

What was fascinating here is not that they used the IEC standard equalization of 35 μs at 15 in/s, which was standard in Europe, but that they also invented their own standard and used 35 μs at 7.5 in/s as well! Not content with that, they invented yet another standard of 50 μs for 3.75 in/s.

The NagraMaster and StellaMaster equalizations are also non-standard and were probably the most widely adopted equalizations after AME, but who knows how widely used this Teac EE equalization was and who knows what tapes are in archives that had this equalization incorrectly applied.

I have been informed that it was only intended for the consumer market.

A client phoned me and said a cassette he was playing started to shed in his machine and he stopped and took it out. He sent it to me and as I pulled a little bit of clear leader out of the middle of the tape, this is what I found:

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

Demagnetizing tape heads and recorder parts is a ritual of magnetic recording. If any part that touches the tape is magnetized beyond a certain level it will begin degrading the tapes played on it.

While early machines may have had an issue with magnetization, most late-model machines rarely become magnetized. The source for real information on this is Jay McKnight’s Magnetic Reference Lab Web site. (more…)

The National Recording Preservation Board has made available a new document Capturing Analog Sound for Digital Preservation. It is an excellent summary document, and we’ve added it to our information page.

I received a cassette from a client and he complained that the previous recording was audible as well as the new recording.

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.

“Noise Reduction” is a potentially confusing topic, partially because it has come to be used to mean two different things.

1. Today, it means removing noise from a recording by means of a single-ended post-production device or plug-in, such as Noise Free Pro by Algorithmix that I use (among other tools).
2. Historically, the term was used for a double-ended process where the dynamic range of the program material was reduced in an unobtrusive way, transported by the noisy channel (be it tape or broadcast) and then expanded in a complementary fashion at the end/output of the noisy channel. These devices were generally referred to as companders (a contraction of compressor/expander).

When reviewing old tapes, they may be marked in various ways to indicate their noise reduction compression, or processing. As of this writing, there are no software plug-ins that accurately mimic the action of the hardware compander acting as an expander. We use actual companders from the original systems when restoring tapes made with these systems.

We currently handle nine different formats from four manufacturers and are always on the lookout for more. Most manufacturers sold a variety of systems tailored to the needs of different kinds of transmission/recording channels

See our special page under formats (click here) to see some of the information we’ve gathered about noise reduction techniques used over the years. Check back as we uncover additional formats and information.