Time constant and cutoff frequency calculator corner frequency RC pad tau and f RIAA NAB CCIR DIN FM conversion cut-off cut off EQ emphasis preemphasis deemphasis

• Frequency response and equalization EQ •

Pre-emphasis and de-emphasis
Conversion: time constant τ to cut-off frequency f_c and
cut-off frequency (corner frequency) f_cto time constant τ

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

Time constant τ in µs	Cut-off frequency f_c in Hz	Equalization emphasis
7958	20	• (RIAA)
3183	50	• RIAA, NAB
1592	100
318	500	• RIAA
200	796
140	1137
120	1326	MC
100	1592
90	1768	MC
75	2122	• RIAA, FM
70	2274
50	3183	NAB, PCM, FM
35	4547	DIN
25	6366
17.5	9095	AES
15	10610	PCM
12.5	12732
10	15915

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

The possible Preemphasis of a PCM recording for DAT oder CD.

The increase of 20 dB per decade is equivalent to the increase of 6 dB per octave.

Cut-off frequency:

Time constante:

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

At the cut-off frequency f_c 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 an auditory (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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