Standard Tape Flux vs Frequency

Jay McKnight

Magnetic Reference Laboratory

    IEC Standard 60094-1, 1981, "Magnetic Tape Sound Recording and Reproducing Systems, Part 1, General Conditions and Requirements", gives the definition and formula for calculating the standard flux levels vs frequency in Clause 15 on page 17. It gives a table of the standard "Time Constants" for each standard speed and use  in Clause 15.1 on page 19, and the actual standard amplitude/frequency response of the recorded short-circuit flux level in decibels in Table 1, on page 27 of IEC 60094-1. We have reproduced that table at  iec94-flux-v-frequency-table.pdf  .

     The MRL publication "Choosing and Using MRL Calibration Tapes for Audio Tape Recorder Standardization" also gives the formula for calculating the flux level vs frequency on page 2 (Sec 1.2.3), and the standard transition frequencies  for use in that formula in Table 1 "Standard Equalizations Per IEC, NAB, and AES Standards", on page 3

    "Choosing and Using...", in Sec. 2.3.3 (page 7 and 8) also gives eight conversion tables for different speeds and equalizations, in case you need to calibrate a system with one speed and equalization standard, but you only have a Calibration Tape for another speed or equalization standard.

    If you need conversion tables not given in "Choosing and Using...", we have posted the Forth program for DOS that we used for calculating them.  You need to download two files: the first is the Forth source code file (magtapeq.seq)  , which is plain text -- you can read it in any text editor, such as "notepad". It gives general instructions for using the executable file,  including a table of serial  numbers for each speed and standard equalization for open-reel systems.

The other file is the executable code (magtapeq.exe), that  takes the serial number of the tape you have , and the serial number of the tape you wish  you had (both found in magtape.seq), and displays on screen, or to a file or a printer, the tables  (like in Table 5 on p 8 of "Choosing and Using...") giving the  frequencies and necessary levels. Type "bye" to exit the program.

This program can be used to calculate a table of standard recorded flux vs frequency by using serial 0 as the "tape you wish you had" -- for instance, enter 11 0  to calculate the NAB flux vs frequency at 15 in/s. To calculate the standard reproducing equalization (assuming that you have an "ideal" reproducing head), enter 0 10 to calculate for an IEC1 reproducer at 15 in/s.

If you can't or don't want to run the Forth DOS program, I've posted the complete results . Look up the speed and equalization numbers  in the Forth source code file (above -- magtape.seq), then find the table that you need in "results".


"magtapeq.exe" is the complete F-PC forth, with software floating point and some other functions compiled on top, then magtapeq.seq compiled on top of that. So you have the complete "works" in magtapeq.exe , and the 3/4 baked instructions in the .seq file. Contact me when you have problems.

Running magtapeq.exe doesn't take any "programming" knowledge, but it is a "command line" program, which can be very frustrating if you end up needing to talk to it, but not knowing the words to say. Call or write if you need help. It's supposed to be easy (ha!).
 Rev  2009-10-18  added "results".