Vol. IV — Electronics · Tool
One resistor and one capacitor set a corner. Low-pass keeps the slow stuff; high-pass keeps the fast. Change R and C — fc, gain, and phase update as you type.
The cutoff (corner) is fc = 1 / (2πRC). At fc the magnitude is −3 dB (about 0.707 of the midband gain). A first-order RC rolls off at 20 dB per decade away from the passband.
Low-pass: series R, capacitor to ground — slow signals pass, fast ones shrink. High-pass: series C, resistor to ground — fast signals pass, DC and slow stuff fall away. Phase at fc is −45° (LPF) or +45° (HPF).
τ = R × C is the same product on RC time. Reactance of C at a chosen f lives on Reactance. Loops and charging curves in the Circuit explorer.