Open the approximation window either by click on "Filter" - "Approximation" or by the toolbar.
- Start/Stop: Define the start and stop frequency for a desired stopband.
- Goal: Define the absorbability for the chosen frequency range.
- Type: Choose the type of the goal.
- Add/Remove Goal: This two buttons allow to add and remove stopbands and passbands to and from the list on the right.
- Solve Approximation: With the Solve Approximation button the optimal solution for the specification will be found.
Note: The defined stopbands and passbands are displayed in blue and red in the graph, respectively.