Why is the default value of the Output Word Length in the FDATOOL of MATLAB 7.1 (R14SP3) different from that in MATLAB 7.0.4 (R14SP2)?

I am using the Filter Design and Analysis Tool (FDATOOL) to set the Input/Output parameters for my filter.

I execute the following steps:

1. Bring up the Filter Design and Analysis Tool by typing 'fdatool' at the MATLAB command prompt.

2. Click on the 'Set Quantization Parameters' icon on the fdatool dialog.

3. In the 'Filter Arithmetic' drop-down menu, select 'Fixed-point'.

4. Select the 'Input/Output' tab.

In the 'Input/Output' tab, I am interested in finding out the value of the 'Output word length' parameter.

In Filter Design Toolbox 6.2 (R14SP2), I see that the default value of this 'Output word length' parameter is 41, whereas in Filter Design Toolbox 6.3 (R14SP3), the default value of the 'Output word length' parameter is 37.

Answer 1

[MathWorks Support Team]

This is the intended behavior in Filter Design Toolbox 6.3 (R14SP3). In Filter Design Toolbox 6.2 (R14SP2), the code to determine the word lengths in full precision mode was conservative (the default value of 'Output word length' was 41). This code was enhanced in Filter Design Toolbox 6.3 (R14SP3) and therefore it comes up with shorter value of the 'output word length' parameter (37), which still achieves full precision.