Technical Papers
- 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)
- 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:
- 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
- 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.