Why does changing the values in the Filter internals pane in the FDATool not affect the displayed step response of the designed filter?

When using fixed-point arithmetic during filter design with the FDATool, changing Filter Internals does not have an effect on the displayed filter response.

Answer 1

[MathWorks Support Team]

The step response in FDATool does not take into account the specified filter internals.

Additional information has been incorporated into the documentation in Release 2009a (R2009a).

For previous releases, to work around this issue, you can use the FILTER function as follows:

1. Generate a MATLAB file for the filter from the Generate MATLAB file option in the File menu : File --> Generate MATLAB file

2. Save the MATLAB file as filterfile.m or any other valid name of your choice.

3. Use the FILTER command as follows:

CustomFilter= filterfile

plot(filter(CustomFilter, [zeros(1,100) ones(1,100)]))    % Computes and plots step response