pyfda¶

Python Filter Design Analysis Tool¶

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.

License¶

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

Installing, running and uninstalling pyfda¶

For details, see INSTALLATION.md.

Binaries¶

Binaries can be downloaded under Releases for versioned releases and for a latest release, automatically created for each push to the main branch.

Self-extracting archives for 64 bit Windows, OS X and Ubuntu Linux are created with `pyInstaller <https://www.pyinstaller.org/>`_. The archives self-extract to a temporary directory that is automatically deleted when pyfda is terminated (except when it crashes), they don’t modify the system except for two ASCII configuration files and a log file. No additional software / libraries need to be installed, there is no interaction with existing python installations and you can simply overwrite or delete the executables when updating. After downloading the Linux archive, you need to make it executable (chmod 775 pyfda_linux).

Binaries for Linux are created as Flatpaks as well (currently defunct) which can also be downloaded from `Flathub <https://flathub.org/apps/details/com.github.chipmuenk.pyfda>`_. Many 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.

pip¶

Supported Python versions are 3.7 … 3.11, there is only one version of pyfda for all operating systems at PyPI. As pyfda is a pure Python project (no compilation required), you can install pyfda the usual way, required libraries are downloaded automatically if missing:

> pip install pyfda

Upgrade:

> pip install pyfda -U

Uninstall:

> pip uninstall pyfda

Starting pyfda¶

A pip installation creates a start script pyfdax in <python>/Scripts which should be in your path. So, simply start pyfda using

> pyfdax

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

**PyQt** and **Qt5**
**numpy**
**numexpr**
**scipy**: 1.2.0 or higher
**matplotlib**: 3.1 or higher
**Markdown**

Optional libraries:

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

conda¶

If you’re working with Anaconda’s packet manager conda, there is a recipe for pyfda on conda-forge since July 2023:

> conda install --channel=conda-forge pyfda

You should install pyfda into a new environment to avoid unwanted interaction with other installations.

Start pyfda with

> pyfdax

git¶

If you want to contribute to pyfda (great idea!), fork the latest version from https://github.com/chipmuenk/pyfda.git and create a local copy using

> git clone https://github.com/<your_username>pyfda

This command creates a new folder pyfda at your current directory level and copies the complete pyfda project into it. This Github tutorial provides a good starting point for working with git repos.

pyfda can then be installed (i.e. creating local config files and the pyfdax starter script) from local files using

> pip install -e <YOUR_PATH_TO_PYFDA_setup.py>

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.

Building pyfda¶

For details on how to publish pyfda to PyPI, how to create pyInstaller and Flatpak bundles, see BUILDING.md.

Customization¶

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/pyfda_rc.py, at the moment you have to edit that file at its original location.

Features¶

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 values as expressions like exp(-pi/4 * 1j) using numexpr syntax

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. Define your own stimuli like abs(sin(2*pi*n*f1)) using numexpr syntax and the UI.
3D-Plots (|H(f)|, mesh, surface, contour) with optional pole / zero display

Modular Architecture¶

Facilitate the implementation of new filter design / analysis / display methods. Generate your own

Filter design widgets with your algorithm
Plotting widgets
Input widgets
Fixpoint filter widgets, using the integrated Fixed() class

Import / Export¶

Filter designs in pickled and in numpy’s NPZ-format
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
Transient stimuli (y[n] tab) as wav and csv files

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 CHANGELOG.md.

Planned features¶

Started¶

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 (help wanted)¶

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, ΣΔ, …) for fixpoint filters with a low number of multipliers (or none at all)
Analysis of different fixpoint filter topologies (direct form, cascaded form, parallel form, …) concerning overflow and quantization noise