This article is from the Audio Professional FAQ, by with numerous contributions by Gabe M. Wiener others.
An MRL is a reference alignment tape from Magnetic Reference Laboratory.
These tapes, available in every conceivable tape speed, tape width,
equalization, and field strength, contain alignment tones useful in
calibrating the electronics of analog tape machines.
These tapes can be ordered from many pro audio dealers. If not, you
can contact MRL directly at:
Magnetic Reference Laboratory, Inc.
229 Polaris Avenue, Suite 4
Mountain View, CA 94043
Tel: (415) 965-8187
Fax: (415) 965-8548
 
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