Welcome to the
Magnetic Reference Laboratory

MAGNETIC REFERENCE LABORATORY, INC.
700 Mill St. #15
Half Moon Bay, CA  94019   USA
Phone: +1-408-227-8631
 
Send orders, comments, and questions to mrltapes@comcast.net,
or call us at the number above.

Attention all MRL Customers and Dealers:


We have completed the move to our new offices, and are in the process of setting up the production system and engineering lab.

We plan to resume production of ¼" and ½” tapes in early February 2024. All tapes will continue to be backordered for at least two weeks, so we will be sending updates to affected customers.

Before resuming production, we will upgrade some key components of the automation system, and then make updated lab samples to confirm that the production system is properly calibrated.

If you have any questions or concerns, please contact our Interim CEO, Jeff McKnight, at: jeff.mcknight@mrltapes.com


Last revised 2024-01-28

Download current price list from https://mrltapes.com/pubpl2023.pdf

Site Contents:
Catalog Pages (Part Numbers)
To Place an Order
MRL Technical Papers Available
More Information on Analog Magnetic Tape Recording
About MRL

Magnetic Reference Laboratory (MRL) makes and sells Calibration Tapes (what is a "Calibration Tape"?) for analog audio magnetic tape reproducers in the Open Reel format. We no longer make Calibration Tapes in the Broadcast Cartridge format – lube tape and carts are no longer available. We also do not make calibration cassette tapes.

On this webpage, you will be able to access all of our literature, which we have made available in the PDF format.
If your browser does not have a built-in PDF/Acrobat reader, you can download a free reader from
Foxit.


Catalog Pages (Part Numbers):

   Which Calibration Tape Should I Buy? An Elementary Guide should help those who are new to analog magnetic tape recording to find the right Calibration Tape for their needs.

   All of our Calibration Tapes are recorded full-track, so they may be used for calibrating reproducers of any track format.

    We make many different sets of test signals, and each is described in one of our "Publications". Within each publication you will find the test signal descriptions, part numbers and prices for various tape widths, speeds, standard equalizations, and lengths.

    We stock dozens of the more popular types of Calibration Tapes, and we can usually make anything not in stock in a few days after receiving an order.

    Here are some examples of the catalog pages describing Calibration Tapes with the more popular test signals:

         Multifrequency (general purpose, for setting reproducer gain, azimuth, and frequency response from 32 Hz to 20 kHz).

         Two frequencies (1 kHz, 10 kHz).

         Three frequencies (1 kHz, 10 kHz, 50 Hz).

         Four frequencies (1 kHz, 10 kHz, 16 kHz, 50 Hz).

         Two-speeds, with many different selections of frequencies.

         Flutter and Speed Test.

    The Complete List of MRL Publications gives all of the other test signals that we can record for you, including Polarity Calibration, special signals for Sound Technology or for Audio Precision measurement systems, Fast Swept-frequency for use with an oscilloscope, Slow Swept-frequency for use with a plotter, single frequencies, Broadband Pink Noise, Broadband White Noise, and Chromatic Sweep for use on your reproducer's vu meter. It also gives an explanation of the MRL Catalog Numbers .

    Choosing and Using MRL Calibration Tapes, a 12-page technical paper, gives a more advanced discussion of general information that applies to all of our calibration tapes. Topics covered include a guide to choosing a Calibration Tape (standards, test signals available, levels, reference fluxivity, and fringing), tape reproducer adjusting techniques (preliminaries, low-frequency response calibration, what to do in case you don't have the right calibration tape), some tape recorder adjusting techniques, and our specifications and tolerances.

    Many other technical papers on magnetic recording are also available online.


To place an order:

    You may order directly from MRL. Contact us by e-mail at mrltapes@comcast.net, or call our order desk at +1.408.227.8631 on weekdays between 09:00 and 17:00 Pacific Time. Orders placed before noon Pacific Time can usually be shipped that day.

    You may pay by major credit card (VISA, Master Card, Discover, or American Express), or by guaranteed funds (money order or cashier's check). For international monetary transfers (which are more expensive), call or email MRL for instructions.

    Delivery: Orders placed before noon Pacific Time can usually be shipped that day, but we can't guarantee it. We have a very small staff (usually one person), and it may occasionally take up to a week to have your order ready to ship. So if you require your order to be shipped by a deadline, place your order at least a week before that date. Don't wait until the last day!

   Sales tax of 9% will be added to orders shipped to Santa Clara County, CA; or 7.25% to orders shipped elsewhere in California. (We are not required to collect, and we do not collect, any other district taxes).

    You may place your order with one of our dealers -- this may be easiest for you if you have an account with them. See the list of MRL USA Dealers or MRL International Dealers. If your favorite dealer's name is not listed, ask him to contact us about becoming an MRL dealer.

Please contact us if you need further information, or have questions that were not answered in this literature.


MRL has been a Sustaining Member of the
Audio Engineering Society since 1976

MRL Technical Papers Available

These papers answer many "frequently asked questions" on using analog tape recorders. They discuss both theoretical and practical matters, and supplement the information given in the manuals for tape recorders. They are available for downloading from this website.

     Tape Recording Equalization:

         Fundamentals and Equalizations for 15 in/s, including suggestions for improved (non-standard) equalizations, with links to several other tech papers.

         Standard Tape Flux vs Frequency (IEC Standard, table of values, and program to calculate differences).

         AME (Ampex Master Equalization curve, with tech information and references on this site).

         Historical Table of Transition Frequencies / Time Constants from 1969 SMPTE paper.

         Master-tape Equalization Revisited.

         Proposed Equalization for 15 in/s Studio Master Recording on High-output Low-noise Tapes.

    "Head bumps" and Low-frequency response -- why the low-end may not sound like what you thought you recorded:

         Low-Frequency Response Calibration of a Multitrack Magnetic Tape Recording and Reproducing System (what happens and why, with measurement techniques)

        Link to Jack Endino's measurements of the "head bumps" of 16 popular studio recorders, running at both 15- and 30-in/s, clearly showing the size and frequency of the "head bumps" (some are pretty frightening)

    Azimuth in a Magnetic Tape Recorder (measurement methods and tolerances)

    Biasing in Magnetic Tape Recording (what ac bias does; how it affects frequency response, distortion, and more)

    Demagnetizing A Tape Recorder

    Head Height Alignment Methods

    Is My Calibration Tape Still Accurate?

    Field Strength for Partial Erasure of Magnetic Tape (how large a field does it take to accidentally erase a tape?)

    Making and using Calibration Tapes, a pair of background papers from Ampex days:

         Bob Morrison's "Reproduce Test Tapes: Evolution and Manufacture"

         Jay McKnight's "Tape Reproducer Response Measurement with a Reproducer Test Tape"

    Speed, Pitch, and Timing Errors in Tape Recording and Reproducing

    "Scrape Flutter" and Tape Compliance Bibliography

    "Sticky-shed" -- tape binder shedding, and what to do about it -- MAJOR UPDATE 2008-01-30

    Tape Information Table, with a summary of coating thickness, coercivity, retentivity, and remanance for 17 professional tapes from Ampex, 3M, and BASF, in consistent (SI) units

The Standards (for instance IEC Standard 60 094, Part 1), and the tape recorder manuals, both say to set up your tape reproducer gain and equalization from a "Calibration Tape" such as MRL makes. But you may have wondered how MRL measures the response and fluxivity in the first place. Well, we do it from first principles that are explained in the technical paper "Flux and Flux-Frequency Measurements and Standardization in Magnetic Recording". Another paper, "Tape Flux Measurement Revisited", explains both an ac and a dc flux measurement in detail, with examples.

MRL President Jay McKnight has published over 70 papers on analog magnetic recording and audio engineering. Topics include the design of magnetic recording heads; the magnetic erasing, recording, and reproducing processes; signal and noise considerations; frequency and wavelength response, measurements, standardization, etc; audio systems and practices; program level indicators; tape transport design, flutter measurement, etc; and miscellany. Many of these were published in the Journal of the Audio Engineering Society. They are listed in the Bibliography of papers by J. McKnight, and many of the PDF files of the papers are linked there.


More Information on Analog Magnetic Tape Recording

    For information on “Recording the Masters” (formerly RMGI or BASF) blank tapes, including the technical specifications, see their webssite at Recordingthemasters.com.

    For information on ATR Magnetics blank tapes, including technical specifications, see their website at ATRTAPE.com.

    For information on the the history of audio engineering (including magnetic tape recording), see the website of the AES Historical Committee.

    For information on all aspects of Ampex tape recorders, see the Ampex Virtual Museum and Mailing List (not affiliated with Ampex Corp).

    For information on Sony/MCI tape recorders, see the Sony/MCI discussion group (not affiliated with Sony Corp).

    For "Tips/Notes/Formats/Resources", see Richard Hess's Web pages.


About MRL

    "Magnetic Reference Laboratory and the State of Reproducer Calibration", by Ralph Hodges, from db magazine, 1980 November.

     "Behind The Gear: Jay McKnight of Magnetic Reference Laboratory", by Alex Kostelnik, from Tape Op, Nr 52 (2006 Mar/Apr).

     Jay McKnight at Ampex, the rest of Alex Kostelnik's interview that was not used in the Tape Op article.

     Jay McKnight's Biography.


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Updates to this home page

2024-01-28 Production updates
2023-12-07 Announcing MRL will be remaining open for business
2023-11-15 Changing MRL closure date to December 01, 2023
2023-10-01 Announcing MRL closure date
2023-03-08 15% price increase on 2023-04-01
2019-07-01 Three-frequency and Four-frequency tapes changed from using 100 Hz to 50 Hz
2019-02-26 Prices increased by 15% on 2019-04-01

2017-07-09

Reformat; add “Contents”, “full track”, “RTM tape”; 100 Hz changed to 50 Hz, updated sales tax; get pdf reader from Foxit