WinIIr is a rather specific tool for people who have to design digital "Infinite Impulse Response" filters.
There are several applications available for this purpose, starting with "MATLAB" ©.
Anyway, WinIIr offers certain advantages:
- This software is completely free !
- The synthesis is precise and correct. It delivers the same results as "MATLAB. This is not always the case for some packages available on the Web…
- It is ergonomic: optimizing a filter while examining its Frequency and Time Responses is easy.
- The filter is calculated and implemented using the "Biquad" architecture. This is the only way for creating high order filters with only a "double float" precision (64 bits). The maximum order is 16.
- Rather than the classical "Step Response", the Time Response diagram shows the response of the filter to a "Sine Wave Burst" at the "Marker" frequency.
- The "Marker" frequency can be modified by displacing a cursor on the screen or by entering the frequency in an edition box.
- The filters are stored on the disk in a human readable text format, Therefore the files are easy to maintain.
- The application includes its own text editor, accessible through the "Filter Editor" button. The description is refreshed in real-time during the design.
- The description file also includes the "c" source code for implementing the filter.
The Main Dialog Box:
Here is a example of the main application screen for an "elliptic" band pass filter of order 8:
The available features are self-explanatory for people accustomed to filter design.
Four types of filters are available, as usual: low pass, high pass, band pass and band stop, with three possible implementations:
Butterworth, Chebyshev and Cauer (Elliptical). For the Chebyshev and Cauer implementations, the maximum ripple must be specified.
For the Cauer filter, specifying the attenuation is also required.
The upper diagram displays the Frequency Response on a linear or logarithmic frequency scale.
The lower diagram displays the Time Response at the selected Marker frequency.
The scale of each abscissa is selected by a small spin control.
The Code Editor:
An Editor is included to access the filter description in text format. It is accessible through the "View Code" button.
Here is an example of the filter description for a simple "high pass" filter:
Here is the synthesis result accessible through the Editor Window:
WinIIr Filter Designed : 2 jul. 2020 at 13:13
Type : High Pass, fc = 5000 @ fs = 48000
Kind : Butterworth, Order 4
Biquad section 1 :
a0 = 1.0000000000000000e+000, b0 = 5.7390163562541840e-001
a1 = -1.0155428255941767e+000, b1 = -1.1478032712508368e+000
a2 = 2.8006371690749693e-001, b2 = 5.7390163562541840e-001
Biquad section 2 :
a0 = 1.0000000000000000e+000, b0 = 7.2725356179509404e-001
a1 = -1.2869054402745597e+000, b1 = -1.4545071235901881e+000
a2 = 6.2210880690581649e-001, b2 = 7.2725356179509404e-001
Analyzing a given filter:
WinIIr can also be used for analyzing a specific filter.
For this purpose, you must "Load” a text file containing the sampling frequency and the biquad parameters.
Here is an example of such a file for a RIAA filter:
Here is the result of the Analyze:
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.
The documentation is available in PDF format (645KB): WinIIr2.0.pdf
WinIIr Setup "zipped" executable file (1.5MB): WinIIr_2.0_Setup.exe.zip
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