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Python Filter Design Analysis Tool

PyPI version Downloads/mo. Total Github Downloads MIT licensed ReadTheDocs build_pyinstaller

pyfda is a tool written in Python / Qt for analyzing and designing discrete time filters with a user-friendly GUI. Fixpoint filter implementations (for some filter types) can be simulated and tested for overflow and quantization behaviour in the time and frequency domain.


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pyfda source code ist distributed under a permissive MIT license, binaries / bundles come with a GPLv3 license due to bundled components with stricter licenses.

Binaries / Bundles

Currently, binaries (created with pyInstaller) are provided for 64 bit Windows and for OS X. The binaries don't modify the system (except for two ASCII configuration files and a log file), they self-extract to a temporary directory that is automatically deleted when pyfda is terminated (except when it crashes). No additionaly software / libraries need to be installed. For details, see

A flatpak (Linux only) for pyfda is available on Flathub. Some Linux distros have built-in flatpak support, for others it's easy to install with e.g. sudo apt install flatpak. For details check the Flatpak home page.


  • Python versions: 3.7 ... 3.10
  • All operating systems - there should be no OS specific requirements.


The following libraries are required and automatically installed by pip when missing.

Optional libraries:

  • mplcursors for annotating cursors
  • docutils for rich text in documentation
  • xlwt and / or XlsxWriter for exporting filter coefficients as *.xls(x) files

Installing pyfda

Unless running a binary, you need to have a working Python installation on your computer, preferrably including the libraries listed above.

There is only one version of pyfda for all supported operating systems, Python and Qt versions. As pyfda is a pure Python project (no binaries, no compilation required), you can install pyfda using one of the following options:


Installation from PyPI works the usual way, required libraries are installed automatically if missing:

> pip3 install pyfda

Upgrade using

> pip3 install pyfda -U

If you have cloned pyfda to your local drive you can install the local copy (i.e. create local config files and the pyfdax starter script) via

> pip3 install -e <>

For more details and options see

You can also download the zip file and extract it to a temp directory of your choice. Install it either to your <python>/Lib/site-packages subdirectory (this creates a copy) using

> python install

or just create a link to where you have copied the python source files (for testing / development) using

> python develop


For development purposes, you should fork the latest version of pyfda from and create a local copy using

> git clone<your pyfda fork>

This command creates a new folder "pyfda" at your current directory level and copies the complete pyfda project into it.

The tutorial at provides a good starting point for working with git repos. As described above, pyfda can then be installed from local files using either

> pip3 install -e <>


> python develop

Now you can edit the code and test it. If you're happy with it, push it to your repo and create a Pull Request so that the code can be reviewed and merged into the chipmuenk/pyfda repo.

Starting pyfda

In any case, a start script pyfdax should have been created in <python>/Scripts which should be in your path. So, simply start pyfda using

> pyfdax


The location of the following two configuration files (copied to user space) can be checked via the tab Files -> About:

  • Logging verbosity can be controlled via the file pyfda_log.conf
  • Widgets and filters can be enabled / disabled via the file pyfda.conf. You can also define one or more user directories containing your own widgets and / or filters.

Layout and some default paths can be customized using the file pyfda/, at the moment you have to edit that file at its original location.


Filter design

  • 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
  • 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

User Interface

  • only widgets needed for the currently selected design method are visible
  • specifications are remembered when switching between filter design methods
  • enhanced matplotlib NavigationToolbar (nicer icons, additional functions)
  • tooltips for all UI widgets and help files
  • 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) (using the numexpr module)

Graphical Analyses

  • Magnitude response (lin / power / log) with optional display of specification bands, phase and an inset plot
  • Phase response (wrapped / unwrapped) and group delay
  • Pole / Zero plot
  • Transient response (impulse, step and various stimulus signals) in the time and frequency domain. Roll your own stimuli (courtesy of numexpr module)!
  • 3D-Plots (|H(f)|, mesh, surface, contour) with optional pole / zero display

Modular Architecture

facilitates the implementation of new filter design and analysis methods. Generate your own

  • Filter design files, containing the actual algorithm and optional GUI widgets
  • Plotting widgets
  • Input widgets
  • Fixpoint filter widgets, using the integrated Fixed() class

Import / Export

  • Export and import 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), as a Matlab (R) workspace or in FPGA vendor specific formats like Xilinx (R) COE-format

Why yet another filter design tool?

  • Education: Provide an easy-to-use FOSS tool for demonstrating basic digital stuff and filter design interactively that also works with the limited resolution of a beamer.
  • Show-off: Demonstrate that Python is a potent tool for digital signal processing as well.
  • Fixpoint filter design: Recursive fixpoint filter design has become a niche for experts. Convenient design and simulation support (round-off noise, stability under different quantization options and topologies) could attract more designers to these filters that are easier on hardware resources and much more suitable especially for uCs and low-budget FPGAs.

Release History / Roadmap

For details, see

Planned features


  • Dark mode
  • HDL filter implementation: Implementing a fixpoint filter in VHDL / Verilog without errors requires some experience, verifying the correct performance in a digital design environment with very limited frequency domain simulation options is even harder.

Ideas (for the not so near future or for )

  • Use audio files as stimuli in the impz widget and store results. Maybe real-time for FIR filters?
  • Keep multiple designs in memory, switch between them, compare results and store the whole set
  • Graphical modification of poles / zeros
  • Document filter designs in PDF / HTML format
  • Design, analysis and export of filters as second-order sections, display and edit them in the P/Z widget
  • Multiplier-free filter designs (CIC, GCIC, LDI, SigmaDelta-Filters, ...) for fixpoint filters with a low number of multipliers (or none at all)
  • Export of Python filter objects
  • Analysis of different fixpoint filter topologies (direct form, cascaded form, parallel form, ...) concerning overflow and quantization noise