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RC filter calculator

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Low-pass

$f_c=\frac{1}{2\pi RC}$ — the −3 dB point, where the output has fallen to 70.7 % of the input. R in series, C to ground: C’s impedance falls as frequency rises, increasingly shorting Vout to ground above fc.

Example Cutoff frequency: 1.592 kHz

Example Nearest E24: R=1 kΩ, C=100 nF → fc = 1.592 kHz (0.0%)

Attenuation at a given frequency (optional)

High-pass

$f_c=\frac{1}{2\pi RC}$ — the −3 dB point, where the output has fallen to 70.7 % of the input. C in series, R to ground: at low frequency C’s high impedance blocks most of the signal from reaching R1; above fc, C behaves like a short and the signal reaches Vout largely unattenuated.

Example Cutoff frequency: 1.592 kHz

Example Nearest E24: R=1 kΩ, C=100 nF → fc = 1.592 kHz (0.0%)

Attenuation at a given frequency (optional)