Equalization—The bulk of the recordings made in the world are NAB (IEC2) equalizations. I say this because the consumer market generally adopted this standard.
Most European professional recordings are recorded with IEC1 equalizations, while the North American recordings were recorded with NAB (IEC2) equalizations. This difference will affect frequency response.
It is interesting to note that early tape recorders did not necessarily have standardized equalizations.
IASA TC-04 Version 2 has detailed information here. Disclaimer: I provided some information for the referenced table.
Ampex Master Equalization (AME) and NagraMaster Equalization are two (and there are several more) proprietary standards that have achieved some widespread use. This PDF file shows a passive AME equalizer that I and a few other mastering engineers have built. There are now two resources relating to AME Larry Miller’s Essay on the topic and Ampex Service Bulletin 15 which is the source (apparently) for the graph in Jay McKnight’s note which I copied into mine.
Nagramaster is a 15 in/s equalization and is clearly stated in the Nagra T-Audio service manual on PDF page 268
it is 3180 & 13.5 µs.
For Teac Extra Efficiency equalization see this Notes Article.
High-density later-generation multi-track tapes
In February 2009, the question of proper equalization for later-generation multitrack recordings (1/2-inch 8-track and 1-inch 16 track) was raised on the Ampex mailing list.
Goran Finnberg confirmed the following from the service manuals:
Tascam MS-16 page 2-1: IEC infinity & 35 µS
Tascam 38 page 35: IEC 1 infinity & 35 µS
Tascam 85-16B page 8-2: IEC infinity & 35 µS
O. J. Rancans confirmed the following:
Tascam TSR-8: Infinity and 35 uS [IEC]
Chris Myring added the following:
At least they were consistent with the 4-track:
TEAC/TASCAM A-3440 15 ips: 3180/50 YTT-1004 test tape
TEAC/TASCAM A-3440 7-1/2 ips: 3180/50 YTT-1003 test tape
TEAC/TASCAM A-3440S no EQ stated but test tapes as above
TASCAM 34 15 ips: 3180/50 YTT-1004 or MRL21J205 test tape
TASCAM 34 7-1/2 ips: 3180/50 YTT-1003 or MRL21T204 test tapeOTARI MX-5050 MkIII-8 15 ips: switchable 3180/50 or inf/35
OTARI MX-5050 MkIII-87-1/2 ips: switchable 3180/50 or inf/70FOSTEX G16S 15 ips only: inf/35
Jay McKnight of Magnetic Reference Lab provided the following insight:
MRL has, to the best of my knowledge, made ALL of the Calibration Tapes for these Tascam 1/2 inch 8 T machines. At first we OEMed them for Tascam,and used their part numbers YTT1144 for half-inch, and YTT1244 for onen inch. Later they sold the identical MRL part 31J229, which is 1/2 in, 15 in/s, IEC, 250 nWb/m, and yet later they just referred people to us directly.
On the “with NAB lo-end” question: The we were approached by Yoshiharu Abe of Teac/Tascam, who originally asked us for IEC HF eq + NAB LF eq. We replied with the arguments against the NAB LF eq — see “The CaseAgainst Low-frequency Pre-emphasis in Magnetic Recording“, and he agreed to use the standard IEC eq. I know that we never made the “special eq” Cal Tape for Tascam, and I’m not aware of their actually making any of the 1/2 in 8T machines with that eq, but it could have happened.
We also spoke to Otari and advised to use IEC eq. But their management said “If Tascam is using IEC, we certainly won’t do the same thing.” So, yes, they used NAB.
But, of course, you can set any tape recorder to NAB or IEC eq with a switch, a jumper, or a component change, depending on the design.
This helps reduce the uncertainty with this format.