WinFIR 1.21

WinIIr is an application for people having to design digital "Finite Impulse Response" (FIR) filters.

•  WinFIR is completely free software.
•  It is easy to use and intuitive for people knowing a little about the "FIR" and their limitations.
•  It is ergonomic: optimizing a filter while examining its Frequency and Time Responses is easy.
• The calculation of the filter coefficients (taps) is based on the classical "Parks-McClellan" algorithm.
• The maximum number of coefficients is 4095.
• The frequency response can be easily examined, by displacing a cursor (Marker) on the graphic.
• The filters are stored on the disk in text format. Therefore the files are easy to maintain..
• For an easy access to the filter coefficients, the application includes its own text editor.
• The coefficients can be modified or new coefficients can be "pasted" in the editor to analyze the frequency response.
• To analyze the real performance of the filter, the coefficients format can be set to 64 bit float or 32 bit float or 32 bit integer or 16 bit integer.

The Main Dialog Box:

The upper diagram displays the Frequency Response
The user can adjust the upper frequency limit, and also the lower frequency on a linear scale.
When clicking on the graphic, a marker is displayed and it can be moved with the mouse.
The marker indicates the level (in dB) at the selected frequency.

Under the graphic showing the Frequency Response, a second graphic displays the filter coefficients.
This is only a coarse indication of their value and distribution, to get an idea.

Five types of filters are available: low pass, high pass, band pass, band stop and half-band filters.

Half-band filters  are often used for "Decimation" and "Polyphase" filtering. 
They can be implemented  very efficiently since ((N-1)/2) - 1 coefficients  are null. 

The edition boxes and the buttons used to specify the filter characteristics are located at the bottom
of the dialog window.
Clicking on the "Create" button starts the filter creation process.

Warning: creating a filter with a lot of coefficients will take a lot of time, up to several minutes,
depending on the performance of your PC.. Be patient!

Once that a filter has been created or analyzed the achieved performances are displayed (attenuation, ripple,...).

Hints: creating a filter is an iterative process. Sometimes, relieving the specifications permits to achieve a better filter.
For example, specifying a large attenuation or a low ripple for a filter with few taps is counterproductive.
Also, do not forget to have a look at the "Edge bandwith", a filter with a lower attenuation and an higher ripple
will have a narrower "Edge bandwith", this means that the transition between the pass band and the stop band will be steeper.

 The Filer Editor:

The editor is used to access the filter description and its coefficients in text format.
It is accessible through the "Filter Editor" button or through the "Analyze" button.
When opened, the text editor is automatically refreshed when the filter parameters are modified.

Here is an example of the, automatically generated, description of a simple "low pass" filter with 119 coefficients in 32 bit integer format.

Filer Analysis:

You can enter any set of coefficients inside the editor and request for the frequency response "Analysis", even if those coefficients are not coherent with the filter specifications. 
You will just receive a warning, but the analysis will be performed and the frequency response curve will be updated.

The process is interactive, you can modify the filter parameters inside the Filter Editor Window and Analyze it again to see the consequences of the modifications.

Example of a simple half-band filter

Documentation

The documentation is available in PDF format (586KB): WinFIR.pdf

Download

WinIIr Setup "zipped" executable file (1.3MB): WinFIR_1.2_Setup.zip

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