dfilt.cascade (Signal Processing Toolbox)

Cascade of discrete-time filters

Syntax

```
Hd = dfilt.cascade(Hd₁,Hd₂,...)
```

Description

Hd = dfilt.cascade(Hd1,Hd2,...) returns a discrete-time filter, Hd, of type cascade, which is a serial interconnection of two or more dfilt filters, Hd1, Hd2, and so on. Each filter in a cascase is a separate stage.

You can also use the nondot notation format for calling a cascade:

```
cascade(Hd1,Hd2,...)
```

Examples

Cascade a lowpass filter and a highpass filter to produce a bandpass filter:

[b1,a1]=butter(8,0.6);            % Lowpass
[b2,a2]=butter(8,0.4,'high');     % Highpass
H1=dfilt.df2t(b1,a1);
H2=dfilt.df2t(b2,a2);
Hcas=dfilt.cascade(H1,H2)         % Bandpass with passband 0.4-0.6
Hcas = 
         FilterStructure: Cascade
                Stage(1): Direct-Form II Transposed
                Stage(2): Direct-Form II Transposed
        PersistentMemory: false

To view details of a stage, use

Hcas.stage(1)
 ans =
     FilterStructure: 'Direct-Form II Transposed'
          Arithmetic: 'double'
           Numerator: [1x9 double]
         Denominator: [1x9 double]
    PersistentMemory: false

To view the states of a stage, use

```
Hcas.stage(1).states
```

You can display states for individual stages only.

dfilt dfilt.df1