FilterLab is an easy tool that allows you to design low pass, high pass, and band pass filters, showing the schematic diagram of a filter circuit with component values and displaying the frequency response.
It has a filter selection wizard that allows to design a filter step by step; first you have to select what type of filter you want to create: low pass, high pass, or band pass; next you have to select the frequency (Hz) and attenuation (dB) for the pass band and stop band in the case of low pass or high pass filter, for the case of band pass filter you have to select the same parameters for lower and upper frequencies; next you have to select the approximation (Butterworth or Chebychev), it will show the order, pass band, attenuation, and actual stop band attenuation for each approximation; next you have to confirm the parameters. The Anti-Aliasing wizard allows you to design analog to digital converters, here you have to select directly the pass band frequency (Hz), sampling frequency (Hz), resolution (bits), and signal to noise ratio (dB). In the chart the approximation results can be overlapped, or you can select in the combo box what approximation you wish to show. When moving the mouse over the chart you can see the frequency of each point of the graph. In the view menu you can select the filter views: frequency, circuit, and spice; frequency view shows the chart, circuit view shows the circuit diagram of the amplifiers, and spice view shows the code; also in the view menu you can see the chart by phase in radians or degrees or view the group delay. The resulting files are saved with extension FLT.