Features:

• Design methods: Equiripple, Firwin, Moving Average, Bessel, Butterworth, Elliptic, Chebyshev 1 and 2 (from scipy.signal and custom methods)
• Second-Order Sections are used in the filter design when available for more robust filter design and analysis
• Remember all specifications when changing filter design methods
• Fine-tune manually the filter order and corner frequencies calculated by minimum order algorithms
• Compare filter designs for a given set of specifications and different design methods
• Filter coefficients and poles / zeroes can be displayed, edited and quantized in various formats
• only widgets needed for the currently selected design method are visible
• enhanced matplotlib NavigationToolbar (nicer icons, additional functions)
• display help files (own / Python docstrings) as rich text
• tooltips for all control and entry widgets
• specify frequencies as absolute values or normalized to sampling or Nyquist frequency
• specify ripple and attenuations in dB, as voltage or as power ratios
• enter expressions like exp(-pi/4 * 1j) with the help of the library simpleeval (included in source files)
• Magnitude response (lin / power / log) with optional display of specification bands, phase and an inset plot
• Phase response (wrapped / unwrapped)
• Group delay
• Pole / Zero plot
• Impulse response and step response (lin / log)
• 3D-Plots (|H(f)|, mesh, surface, contour) with optional pole / zero display
• Filter design files not only contain the actual algorithm but also dictionaries specifying which parameters and standard widgets have to be displayed in the GUI.
• Special widgets needed by design methods (e.g. for choosing the window type in Firwin) are included in the filter design file, not in the main program
• Save and load filter designs in pickled and in numpy's NPZ-format
• Export and import coefficients and poles/zeros as comma-separated values (CSV), in numpy's NPY- and NPZ-formats, in Excel (R) or in Matlab (R) workspace format
• Export coefficients in FPGA vendor specific formats like Xilinx (R) COE-format