A low-pass filter lets slow-changing signals pass while reducing fast variations. In this RC LPF, a 1 kΩ resistor is in series with the input, and a 1 µF capacitor is connected to ground at the output. At low frequencies, the capacitor charges and discharges slowly, so almost the full input appears at the output with little phase shift. As frequency increases, the capacitor starts reacting faster and diverts more signal to ground, reducing output amplitude. The cutoff frequency is set by fc = 1