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Discrete-time, direct-form II filter


Hd = dfilt.df2(b,a)
Hd = dfilt.df2


Hd = dfilt.df2(b,a) returns a discrete-time, direct-form II filter, Hd, with numerator coefficients b and denominator coefficients a.

Hd = dfilt.df2 returns a default, discrete-time, direct-form II filter, Hd, with b=1 and a=1. This filter passes the input through to the output unchanged.


The leading coefficient of the denominator a(1) cannot be 0.

The resulting filter states column vector is



Create a direct-form II discrete-time filter with coefficients from a fourth-order lowpass Butterworth design:

[b,a] = butter(4,.5);  
Hd = dfilt.df2(b,a)

Introduced before R2006a

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