CR Filter's Response (Analog) An applet to calculate Frequency and Step response for CR Filter: Please drag and drop components onto the circuit. Then Click "Get Res" to get Frequency response. You can also get Step response by choosing the pull-down menu. How to change the value of resistance is double-clicking the component. If this applet looks something weird, please reload it. Upgraded on 04 September, 2005 (ver. 1.2).