Signal Processing Toolbox™

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 (Hd3) to the end of an existing cascade (Hd), use

Hd = addstage(Hd3)

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
Hcas = 
         FilterStructure: Cascade
                Stage(1): Direct-Form II Transposed
                Stage(2): Direct-Form II Transposed
        PersistentMemory: false

To view details of the first stage, use

info(Hcas.Stage(1))

Discrete-Time IIR Filter (real)                
-------------------------------                
Filter Structure    : Direct-Form II Transposed
Numerator Length    : 9                        
Denominator Length  : 9                        
Stable              : Yes                      
Linear Phase        : No                 

To view the states of a stage, use

Hcas.stage(1).states

You can display states for individual stages only.

See Also

dfilt, dfilt.parallel, dfilt.scalar

dfilt

dfilt.delay