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Cassette Equalization: The 4 dB ambiguity at 16 kHz

Filed under: cassettes,Tape Aging — 2006-05-17 by Richard L. Hess — Last Edit 2012-12-03 by Richard L. Hess

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. There is further discussion from 2010 here.

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…)

Mono and stereo cassettes

Filed under: archival practices,cassettes — 2008-05-22 by Richard L. Hess — Last Edit 2012-10-28 by Richard L. Hess

The format page for 0.15 inch wide tape has a drawing (click for large version) that clearly shows that mono cassettes have one wide track and stereo cassettes split this track in half and add a small guard band. Most mono cassette recorders follow this format. It turns out that the mono Marantz PMD201 uses a two-channel head and records dual mono. Most other mono recorders seem to follow the standard.

While this is a theoretical problem, few if any good mono recorders are available for reproducing these tapes anyway, so most of us in the domain transfer field use good quality stereo machines for all cassette transfer work.

UPDATE 2012: While it is often possible to sum the channels if the Dragon finds proper azimuth, on many low-quality tapes this proper azimuth is not achieved. Now that azimuth correction (at least the time delay portion) is available for a reasonable price in iZotope RX2 Advanced, I have found that after correcting for time delay between channels that I can now sum both (if they are worthy of it) and reduce the noise prior to applying the noise reduction plug-in. (more…)

Tape recorder bias frequencies

Filed under: cassettes,recording/mastering,reels — 2008-02-02 by Richard L. Hess — Last Edit 2012-03-25 by Richard L. Hess

The discussion of what bias frequencies were used over time keeps recurring. Special thanks to Jay McKnight of Magnetic Reference Lab, Tom Fine, and Brian Roth  for input to this list. I posted this to the ARSC list, but wanted to include it here as well. This knowlege is useful for those who wish to archive the bias along with the audio for future application of time-base-error correction tools such as the Plangent Processes.

Bias frequences started low, apparently with 60 kHz for early consumer recorders, but Ampex started with 100 kHz. Other later machines used different bias and erase frequencies. We can see with a few exceptions, the top bias frequencies were commonly limited to 250 kHz for audio, with the Sony APR series and the Ampex ATR series in the 400 kHz region. For cassettes, a practical maximum appears to be about 150 kHz. Much higher frequencies (up to at least 8 MHz) were used in instrumentation recorders. An enumeration of several machines follows. (more…)

Slow speed 4-channel cassette digitization

Filed under: loggers,loggers — 2008-02-23 by Richard L. Hess — Last Edit 2011-11-12 by Richard L. Hess

There has been some discussion recently about the 4-channel cassette recorders that were used for court reporting and other logging- or court-reporter-type applications. It seems that the players only have one output and can select any combination of one or more playback channels into that one output.

This monitoring topology is actually identical to two 1-inch 40-channel reel-to-reel logging machines I have where one can listen to any combination of one through forty tracks on a single output. (more…)

Is it really a Phillips screw or is it a Pozidriv screw?

Filed under: Nakamichi Dragon,tools — 2006-03-06 by Richard L. Hess — Last Edit 2010-10-20 by Richard L. Hess

Many pieces of equipment with cross-headed screws actually have Pozidriv screws rather than Phillips screws in them. This is especially true of Japanese equipment. [EDIT 2007-11-26] Or are these yet different JIS screws? See the updated post about this here.

I bought a set of Hozan [JIS] drivers, but now that I’ve learned that PB makes them [maybe] (see tools article) I’ll buy any additional ones from them. Pozidrive screws have “tick” marks between the slots–or should.

Here is an interesting explanation of the different screw heads in the context of cabinet/furniture making.

After some testing with both Phillips and Pozidrive drivers, it seems that some/many of the inexpensive screws that come packaged with home hardware-type items are non-descript and perhaps don’t meet either standard!

IASA TC04 Guidelines on the Production and Preservation of Digital Audio Objects available online.

Filed under: archival practices,cassettes,computer/data,digital,education,history,reels,Tape Aging — 2010-10-08 by Richard L. Hess — Last Edit 2010-10-08 by Richard L. Hess

The International Association of Sound and Audiovisual Archives (IASA) has released their landmark Guidelines on the Production and Preservation of Digital Audio Objects as a free web (HTML) edition, available here.

I provided some information for the listing of tape equalizations, and I find the compiled table (here) most useful.

Thanks to Kevin Bradley and the IASA team for their work in making this available. If you want a PDF copy, join IASA and it’s available.

Cassette equalization redo

Filed under: cassettes,history,Tape Aging — Richard L. Hess — Last Edit 2010-10-08 by Richard L. Hess

There has been much discussion on some web fora about the differences between different brands’ cassette equalization standards.

As I stated here in 2006, there is a 4 dB ambiguity at 16 kHz.

Many things conspire to make this 4 dB ambiguity essentially meaningless in a generally low-fi medium. The only reason I’m mentioning this now is that I’ve been bombarded with email from more than one participant in this discussion and apparently there may be some editorial judgment attached to what is posted.

Jay McKnight has graciously permitted my posting of his comments to me: (more…)

Five historic standards now linked from the history page

Filed under: cartridges,cassettes,history,reels — 2008-08-21 by Richard L. Hess — Last Edit 2008-08-21 by

About two years ago, I asked the EBU to make available a copy of their historic document, Review of existing systems for the synchronisation between film cameras and audio tape-recorders and they complied, making it available on their website.

I asked the National Association of Broadcasters about their Cartridge, Cassette, and Reel tape standards as well as their Disc standard and they gave me permission to post these standards at my website.

These five standards plus some other articles of historic interest are available here in the history portion of this website. I hope that you find these of use in unraveling some of the challenges that old media present.

Magnetic Tape Splicing

Filed under: archive operations,cassettes,reels — 2008-01-07 by Richard L. Hess — Last Edit 2008-06-05 by

I received an email asking me to discuss tape splicing. Most of my work is now repairing old splices so I try and butt them together as best I can in an Edi-Tall block and use the blue Quantegy splicing tape (which will become harder to find with Quantegy exiting the business). I will not be evaluating a replacement for several years as I bought a large supply a few years ago. (more…)

Loading C-0 cassettes

Filed under: cassettes — 2006-03-06 by Richard L. Hess — Last Edit 2008-06-05 by

One way of loading C-0 cassettes is to unscrew the shell and drop the old tape into the new shell.

I have found that reloading using a modified cassette machine is much faster and easier. The following images should explain the process:

Splice one end of the original tape into the C-0:

splice original into c0


Project Notes: Advanced oxide delamination of a cassette

Filed under: cassettes,project notes,Tape Aging — 2006-03-31 by Richard L. Hess — Last Edit 2008-06-05 by

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…)

Aligning a tape recorder

Filed under: archival practices,cassettes,recording/mastering,reels — 2008-02-02 by Richard L. Hess — Last Edit 2008-06-03 by

It seems some people new to tape are confused over how to align a tape recorder. This is the abbreviated version.

If you want to record on a tape recorder (and I do not recommend doing that these days as you’re just generating more tapes that will need to be transferred later) the first thing to do is get the playback correct.

  1. CLEAN the machine. (more…)

Cross-point screws take two: JIS vs. PoziDriv

Filed under: Nakamichi Dragon,tools — 2007-11-26 by Richard L. Hess — Last Edit 2007-11-26 by

I received the following in an email from a person only identified as Ross. I thank him. He sent me the following in reference to this post. concerning Philips and PoziDriv screws as used on Nakamichi Dragons and other Japanese equipment. I, too, have a set of Hozen drivers which I obtained from (more…)

Noise reduction plug-ins

Filed under: archival practices,cassettes,Nakamichi Dragon,reels — 2006-07-24 by Richard L. Hess — Last Edit 2006-07-24 by

The question seems to regularly arise on mailing lists and chat rooms about Dolby and dbx plug-ins. I don’t think it will happen and I added that comment and some hopefully helpful operational hints to my noise-reduction page, here.

Project Notes: Crosstalk on a cassette

Filed under: cassettes,project notes,reels — 2006-03-23 by Richard L. Hess — Last Edit 2006-03-26 by

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.

Demagnetizing recorders and heads

Filed under: archival practices,cassettes,reels — 2006-03-24 by Richard L. Hess — Last Edit 2006-03-24 by

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…)

Analog "Warming up" of sound & the use of obsolete formats in contemporary recordings

Filed under: archival practices,cassettes,digital,recording/mastering,reels — 2006-03-14 by Richard L. Hess — Last Edit 2006-03-21 by

I received a phone call today from someone who wanted my opinion on a Tascam 238 8-track cassette recorder for recording his music.

This was like the person who wanted to know about the DCC recorder for the same purpose yesterday.

People keep hearing that “analog sounds great” or that this or that format “sounds great” and they want to buy in. (more…)

Noise Reduction Basics

Filed under: archival practices,cassettes,reels — 2006-03-18 by Richard L. Hess — Last Edit 2006-03-20 by

\”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.

How to archive recordings — a quick guide to resources on this site

Filed under: archival practices,cassettes,computer audio,digital,recording/mastering,reels — 2006-03-15 by Richard L. Hess — Last Edit 2006-03-20 by

You’ve been asked to digitize recordings in your collection and don’t have any idea where to start. There are  several resources on this site which might be of use.  

What I use is shown on my facility page. That\’s one of the main reasons it is there. If I’m using it, it’s because I like it or it solves a problem for me. If I’m not using it, either I don’t have an opinion about it, won’t spring for it, or don’t like it. (more…)

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