If you’re not interested in an accessible exploration of the RC voltage formula, you can skip ahead to the paragraph marked with a “fast forward” pictogram (⏩). The final and working formula for capacitor voltage is:\(V_{cap}(t) =V_{supply} \cdot (1 - e^{{-t \over RC}})\)⏩ If you’re trying to skip the explanation of the RC formula, resume here. On that slope, with every doubling of the signal frequency, the amplitude of the output signal is halved. In the filter, R is constant; meanwhile, X C approaches infinity at 0 Hz and then decreases with signal frequency. With other waveforms, the output of an RC filter wouldn’t be phase-shifted.