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From: david t53 on 17 Jun 2010 17:15
Hello,

I use filterbuilder to design a low-pass filter, IIR,
and I check the option "Scale SOS filter coefficients to reduce chance of overflow" (I use all the other default options).
I click "Apply", and it correctly generates the filter, in a "Hlp1" variable.

Then (still in filterbuilder), I click on "Code Generation"->"Generate M-file". This generates the following file:
h = fdesign.lowpass('fp,fst,ap,ast', 0.45, 0.55, 1, 60);
Hd = design(h, 'butter', 'MatchExactly', 'stopband');

Hlp1 and Hd should be the same but they are not.
The reason for that is because filterbuilder forgets to add the "SOSScaleNorm" and "SOSScaleOpts" options in the generate m file.

That is, if I uncheck the "Scale SOS filter coefficients to reduce chance of overflow" option in filterbuilder, then Hlp1 and Hd are exactly the same.

Doing:
> help(h,'butter')
I see that SOSScaleNorm can be 'l1', 'Linf', 'L2', 'l2', 'L1' or 'linf',
and SOSScaleOpts is a structure with sosReorder, MaxNumerator, NumeratorConstraint, OverflowMode, ScaleValueConstraint and MaxScaleValue properties.

So,
when I click on "Scale SOS filter coefficients to reduce chance of overflow" in filterbuilder,
which "SOSScaleNorm" and "SOSScaleOpts" options is filterbuilding using when clicking on "Apply"?
(these options should be in the generated m file; I guess that this a buf in filterbuilder)

Best regards,
David
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