REFERENCE LABORATORY, INC.
c/o Booye, 165 Wyandotte Dr, San
Jose, CA 95123 USA
Phone and FAX +1.408.227.8631
Which Calibration Tape Should I Buy?
People who are new to analog magnetic tape recording and who are
their first MRL Reproducer Calibration Tape often ask "Which
Tape should I buy? The 'Multifrequency' tape with some 18 to 20
Or a shorter and cheaper 2-, or 3-frequency tape? In the 4-minute or
An Elementary Guide
The best one for you depends on the tape recorder that you
your skill in making the adjustments. Here's some elementary
to help you make those decisions. For more advanced information, see "Choosing
and Using MRL Calibration Tapes for Audio Tape Recorder
First, you need the
Manual for your tape recorder
You should have the Operation and Maintenance Manual for your
before attempting to make measurements and adjustments on it. The
will tell you what mechanical and electronic adjustments there are,
they do, where to find them, and how to adjust them. All tape recorders
have the same basic adjustments, but their locations and adjustment
are usually specific to each machine.
Second, you need to know your
parameters: the tape width, speed, equalization, and reference fluxivity
Most recorders can be set up for any of several
speeds, equalizations, and reference fluxivities ("recording levels").
Each of those takes a different Calibration Tape. Therefore the recorder
model number is no help to you or us in
determining what Calibration
Tape you need.
- The information you need may be on
the front panel of
recorder, or in the
manual, but more often it is not stated, so you have to figure it out
If you have recently purchased a used recorder, the previous owner may
be able to help you.
- If you are already using an MRL
Calibration Tape, the label and
announcement on that tape give the width, speed, equalization and
If you just want to replace that tape, the part number on it will still
-- MRL part numbers have never changed, so you can
reorder the same part number.
- If you have another manufacturer's old
Calibration Tape that was used
setup your reproducer -- Ampex, BASF (Emtec), Standard Tape Lab, et al
-- it will give the necessary information. Call or email us with their
part number or specifications, and we can give
you the equivalent MRL part number.
- If none of these are available, you can
measure the tape width with a
For speed, you can make a mark on the tape; using a watch, "play" the
for one second, then measure how far the tape moved. (This is pretty
but you should be able to tell whether the tape moved 3.75 in, 7.5 in,
in, or 30 in.) Look at the head faces, and see how many
tracks there are -- often knowing the track configuration will give us
to the equalization likely used.
- If all of these methods fail, a service
technician or a knowledgeable
should be able to help you.
The equalizations are known by the standardizing organizations'
and those organizations
have changed their names over the years, resulting in some confusion.
The organization names have changed more often than the equalizations!
The names and
- For 3.75 in/s recording, the same
equalization is used everywhere for
recordings; it is standardized by both the NAB and the IEC, so we call
it "NAB and IEC".
- For 30 in/s recording, the
equalization used everywhere for new
is AES, also called IEC2.
- For 7.5- and 15-in/s recording, the
equalizations used are
- NAB, which is mostly used in the US; it
is now officially called IEC2.
- IEC or CCIR or DIN Studio (all are the
same), which is mostly used in
it is now officially called IEC1.
- For 15 in/s recording, the exception is
that with 8-track recorders on
½-inch tape, and 16- and 24-track recorders on 1 inch tape, the
IEC1 (IEC and CCIR and DIN Studio) equalization is almost always
- During the early years of tape recording
(1948 thru roughly 1968), some
of the equalizations were changed several times, especially at the
speeds, as new-and-improved tapes were developed. Contact MRL for
if you are transcribing recordings made before 1970, and you're not
what equalization to use.
What reference fluxivity should I use?
The "reference fluxivity" section of a Calibration Tape is
normally used to set the reproducer gain on a tape recorder with a vu
meter so that the output level reads 0 dB. The reference fluxivity you
should use depends on:
For some specific recommendations, see the literature from the
manufacturer of the tape you'll be using, and also see MRL's Choosing and
Using MRL Calibration Tapes...., Sec. 1.2.6 and Table 2
(pages 4 and 5).
- your program level meter (whether
a standard vu meter, a standard peak program meter, or something
- the kind of blank tape you'll be using;
- whether you'll be using a noise
reduction system (e.g., Dolby, dBX); and
- whether you desire "tape compression."
Common usages are 200
nanowebers per meter [nWb/m]
for older and consumer-type tapes; 250 nWb/m for general studio usage;
and 500 nWb/m with the highest output mastering tapes when "tape
If you have a Calibration Tape that is not at the reference
that you want, but is otherwise correct, you can easily use it to set
for a different reference fluxivity by the method shown in Choosing
and Using..., Sec. 2.3.1 "Shifting the Reference Fluxivity".
Which test signals should I use?
These tapes are the "old traditional alignment tapes" sold by
others since 1948. They have 18 or 20 shorter tones -- 1 kHz level set,
8- and 16-kHz azimuth set and
preliminary frequency response, and 13 frequencies from 32 Hz to 20
for frequency response. The 13 frequency response tones measure the
response over the entire audio
spectrum, and are necessary for diagnosis and repair of reproducers
poor frequency response. They are also needed to set up a reproducer
the equalization is not already known to be adjusted close to optimum.
An example would be calibrating a newly-purchased machine for the first
time. Though more expensive, multifrequency tapes are the most
Once a reproducer is set up with a Multifrequency Calibration
routine checks at 1 kHz and 10 kHz are usually adequate, and those
are shorter, and therefore both less expensive to purchase, and quicker
This is the minimum set of tones to calibrate a tape reproducer.
1 kHz tone to set the "Reproducer Gain" (which may be called
Level") control. Use the 10 kHz tone first to set the mechanical
of the reproducing head, then to set the "High Frequency Reproducer
These tapes come in 4-minute lengths (2 minutes each of
and 10 kHz); and 8-minute length (4 minutes for each tone). If you know
how to do the adjustments, and they only need be trimmed, two minutes
more than long enough to set two channels. It is not nearly long enough
to set 24 channels, nor even to set two channels if the machine is
out of adjustment. You have to decide how much money it is worth to you
to avoid rewinding the calibration tape several times because you run
of tape before you have finished the adjustments.
These tapes add a 100 Hz tone, at the cost of reducing the tone
from 2 minutes each to 72 seconds each; or from 4 minutes each to 152
The commonly-used 100 Hz tone gives a good test that the low-frequency
the reproducer has not failed. On the other hand, 100 Hz is really too
high a frequency for setting the low-frequency reproducer equalizer
Also, once the low-frequency response is set, it should not require
In fact, some tape reproducers do not even have a low-frequency
control. See Choosing
and Using... , Sec 2.2 "Low-frequency Response Calibration", for
Do I Need a Separate
Each Speed and Equalization?
In general, yes -- we recommend a separate Calibration Tape for
each speed and equalization that you need
The Multifrequency Calibration Tapes are only available in single
speed and equalization. The two- and three-frequency tapes, and
some others, are
available as two-speed
It is possible to use a Calibration Tape for several
speeds and equalizations other than the one it is designed for, but it
makes the procedure more complicated and less accurate than having the
correct tape. See Choosing
and Using... , Sec. 2.3.2 "Shifting the
Other and Special-purpose
For other and special purpose Calibration Tapes, see Sec 1.2.4
in Choosing and
Using MRL Calibration Tapes.... There you
will find calibration tapes with many different special test
single tones, fast and slow sweeps, Chromatic Sweeps, special sweeps
Sound Technology and for Audio Precision analyzers, broadband white or
pink noise, and a polarity calibration tape.
2003-09-02 Minor rev 2005-06-16, 2006-11-06