[Scilab-users] ffilt Description

[George.Rasko at microchip.com]

Hi.

Is there someone out there with more details/understanding about
the filter design done by the ffilt command?
Specifically, for example, if one does


x=ffilt("lp",5,0.1)


n  the five coefficients are obviously not for a simple "boxcar" filter.

Is this a butterworth design? Is there a reference for what this

command is actually implementing?

n  What is the definition of the cutoff frequency for ffilt?

If you take the above example and

[a,b] = frmag(x,500);

plot (a)

the first zero of amplitude is around 222 Hz, but the

0.1   cutoff frequency would be at 100 Hz for 1000Hz sampling.
Is the cutoff frequency defined as ln(2) of the DC response?

n  Why are the coefficients not normalized to give

a DC response amplitude of 1? Isn't that the standard

approach for filter design?

Thanks in advance.
G




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