Deutsche Version

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The Greek letter for the time constant is tau = τ and 1 microsecond is 10⁻⁶ seconds.

Cut-off frequency:

Time constant:

Conditional equations:
Cut-off frequency f_c in Hz = 159155 / τ in µs
Time constant τ in µs = 159155 / f_c in Hz

At the cut-off frequency fc of a drop the voltage V is always fallen to the value of 1/√2 and the voltage level is damped to 20 · log(1/√2) = (−)3,0103 dB.

AME - Ampex Master Equalization Curve

There was also an "Ampex Master Equalization" around the year 1958, called AME.
It was based on modifying the NAB response with a hearing curve, which resulted
in a recorded flux that had a "hump" (re the NAB EQ) from about +3 dB at 630 Hz to
+8 dB at 2 kHz, back to +3 dB at 5 kHz, and down to −12 dB at 16 kHz; see the AME curve:
http://home.comcast.net/~mrltapes/pubame.pdf
http://www.richardhess.com/tape/ame_equalizer_20040412.pdf

In USA FM radio has a time constant of 75 µs, but also in Korea,
Taiwan, Thailand, AFN worldwide and the rest of America.
In Europe FM radio has a time constant of 50 µs,
but also in Africa, Asia (without Korea, Taiwan, Thailand), Pacific.

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