MAGNETIC REFERENCE LABORATORY, INC.
165 Wyandotte Dr, San Jose, CA 95123 USA
Phone and FAX +1.408.227.8631
Send orders, comments, and questions to MRL at mrltapes@comcast.net, or call us at the number above.
Last revised 2019-07-01

Welcome to the
Magnetic Reference Laboratory
Home Page

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 don’t do cassettes .

This page will lead you to all of our literature, which we have put into the PDF format. 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 usually record our Calibration Tapes on SM911 tape by “Recording the Masters” (formerly called RMGI, and BASF). On request, for a small premium we can make our Calibration Tapes on "ATR Magnetics" tape (see announcement ) -- our prices on ATR Magnetics prices are here .

●    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; and

     ○    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 http.//mrltapes.com, or call or FAX 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 to 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)

●    

●    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 Laborat ory 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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