# Documentation

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# dfilt.cascade

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`, etc. Each filter in a cascade is a separate stage.

To add a filter (`Hd1`) to the end of an existing cascade (`Hd`), use

`addstage(Hd,Hd1)`

and to reorder the filters in a cascade, use the stage indices to indicate the desired ordering, such as.

```Hd.stage = Hd.stage([1,3,2]); ```

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-passband .4-.6 ```

To view details of the first stage, use

`info(Hcas.Stage(1)) `

To view the states of a stage, use

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

You can display states for individual stages only.

## See Also

#### Introduced before R2006a

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