RC Filter Calculator

Calculate resistor and capacitor values for first-order high-pass and low-pass RC filters with cutoff frequency and rolloff characteristics.

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How It Works

First-order RC filters have a cutoff frequency fc = 1/(2πRC) where the signal is -3 dB. Low-pass: capacitor to ground (passes lows, blocks highs). High-pass: capacitor in series (blocks DC and lows, passes highs). Slope is 6 dB/octave (20 dB/decade). Common audio uses: DC blocking caps on outputs (HPF at ~1-10 Hz), rumble filters (HPF at 20-80 Hz), and EMI filters (LPF above 100 kHz). For steeper slopes, cascade multiple stages or use active (op-amp) filters for 12-24 dB/octave.