Hd = dfilt.df1(b,a) returns a discrete-time, direct-form I filter, Hd, with numerator coefficients b and denominator coefficients a. The filter states for this object are stored in a filtstates object.

Hd = dfilt.df1 returns a default, discrete-time, direct-form I filter, Hd, with b=1 and a=1. This filter passes the input through to the output unchanged.

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

Image of direct form one filter diagram

Diagram of a direct form one filter

To display the filter states, use this code to access the filtstates object.

Hs = Hd.states       % Where Hd is the dfilt.df1 object and
double (Hs)          % Hs is the filtstates object

The vector is

Examples

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

[b,a] = butter(4,.5);  
Hd = dfilt.df1(b,a)

  FilterStructure: 'Direct-Form I'
     Numerator: [0.0940 0.3759 0.5639 0.3759 0.0940]
   Denominator: [1 -3.6082e-016 0.4860 3.6545e-017 0.0177]
PersistentMemory: false

dfilt.df1 - Discrete-time, direct-form I filter

Syntax

Description

Examples

See Also

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