dfilt.df1 (Signal Processing Toolbox)

Discrete-time, direct-form I filter

Syntax

```
Hd = dfilt.df1(b,a)
Hd = dfilt.df1
```

Description

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.

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 coefficents 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.cascade dfilt.df1sos