Discrete-time filter
Hd = dfilt.
structure
(input1,...)
Hd = dfilt.
returns
a discrete-time filter, structure
(input1,...)Hd
, of type structure
.
Each structure takes one or more inputs. If you specify a dfilt
.structure
with
no inputs, a default filter is created.
Note
You must use a |
Hd = [dfilt.
returns
a vector containing structure
(input1,...),dfilt.structure
(input1,...),...]dfilt
filters.
Available structures for the dfilt
object
are shown below. The target block for the block
method
depends on the filter structure. Depending on the target block, the DSP System Toolbox™ software
may be required.
dfilt.structure | Description | Coefficient Mapping Support in realizemdl | Target Filter Block for |
---|---|---|---|
Delay | Not supported | Delay Requires DSP System Toolbox | |
Direct-form I | Supported | Discrete Filter | |
Direct-form I, second-order sections | Supported | Discrete Filter Requires DSP System Toolbox | |
Direct-form I transposed | Supported | Discrete Filter | |
Direct-form I transposed, second-order sections | Supported | Biquad Filter Requires DSP System Toolbox | |
Direct-form II | Supported | Discrete Filter | |
Direct-form II, second-order sections | Supported | Discrete Filter | |
Direct-form II transposed | Supported | Discrete Filter | |
Direct-form II transposed, second-order sections | Supported | Biquad Filter Requires DSP System Toolbox | |
Direct-form FIR | Supported | Discrete FIR Filter | |
Direct-form FIR transposed | Supported | Discrete FIR Filter | |
Direct-form symmetric FIR | Supported | Discrete FIR Filter | |
Direct-form antisymmetric FIR | Supported | Discrete FIR Filter | |
Overlap-add FIR | Not supported | Overlap-Add FFT Filter Requires DSP System Toolbox | |
Lattice allpass | Supported | Not supported | |
Lattice autoregressive (AR) | Supported | Allpole Filter Requires DSP System Toolbox | |
Lattice autoregressive moving- average (ARMA) | Supported | Not supported | |
Lattice moving-average (MA) for maximum phase | Supported | Not supported | |
Lattice moving-average (MA) for minimum phase | Supported | Discrete FIR Filter | |
State-space | Supported. | Not supported | |
Scalar gain object | Supported | Gain Requires DSP System Toolbox | |
Filters arranged in series | Supported | Target blocks depend on filter structures in the series | |
Filters arranged in parallel | Supported | Target blocks depend on filter structures in the parallel system |
For more information on each structure, use the syntax help
diflt.
structure
at the MATLAB^{®} prompt
or refer to its reference page.
Methods provide ways of performing functions directly on your dfilt
object
without having to specify the filter parameters again. You can apply
these methods directly on the variable you assigned to your dfilt
object.
For example, if you create a dfilt
object, Hd
,
you can check whether it has linear phase with islinphase(Hd)
,
view its frequency response plot with fvtool(Hd)
,
or obtain its frequency response values with h=freqz(Hd)
.
You can use all of the methods below in this way.
Note
If your variable is a 1-D array of |
Some of the methods listed below have the same name as Signal Processing Toolbox™ functions and they behave similarly. This is called overloading of functions.
Available methods are:
Method | Description |
---|---|
Adds a stage to a | |
The
| |
Returns the series combination of two | |
Returns the filter coefficients in a structure containing
fields that use the same property names as those in the original | |
Converts a | |
Writes a filter coefficient ASCII file. The file can
contain a single filter or a vector of objects. Default filename is
| |
Returns the frequency-domain coefficients used when filtering
with a | |
Performs filtering using the
| |
Returns the type (1-4) of a linear phase FIR filter. | |
Plots the frequency response in | |
Plots the group delay in | |
Plots the impulse response in | |
Returns the length of the impulse response. | |
Displays brief | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns a logical | |
Returns the number of sections in a second-order sections
filter. If a multistage filter contains stages with multiple sections,
using | |
Returns the number of stages of the filter, where a stage is a separate, modular filter. | |
Returns the number of states for an object. | |
Returns the filter order. If | |
Returns the parallel combination of two | |
Plots the phase response in | |
(Available only with Simulink software.)
The following properties are available:
The
following properties optimize the block structure. Specifying
| |
Removes a stage from a cascade or parallel | |
Overwrites a stage of a cascade or parallel | |
Converts the
| |
Converts the | |
Plots the step response in
| |
Converts the | |
Converts the | |
Plots the zero-phase response in | |
Converts the | |
Plots a pole-zero plot in |
For more information on each method, use the syntax help
diflt/
method
at the MATLAB prompt.
As with any object, you can use get
to view
a dfilt
properties. To see a specific property,
use
get(Hd,'property')
To see all properties for an object, use
get(Hd)
To set specific properties, use
set(Hd,'property1',value,'property2',value,...)
Note that you must use single quotation marks around the property name.
Alternatively, you can get or set a property value with Object.property
:
b = [0.05 0.9 0.05]; Hd = dfilt.dffir(b); % Lowpass direct-form I FIR filter Hd.arithmetic % get arithmetic property % returns double Hd.arithmetic = 'single'; % Set arithmetic property to single precision
To create a copy of an object, use the copy
method.
H2 = copy(Hd)
Note
Using the syntax |
To change the filter structure of a dfilt
object Hd
,
use
Hd2=convert(Hd,'structure_string');
where structure_string
is any valid structure
name in single quotation marks. If Hd
is a cascade
or parallel
structure,
each of its stages is converted to the new structure.
Two properties control the filter states:
states
— stores the current
states of the filter. Before the filter is applied, the states correspond
to the initial conditions and after the filter is applied, the states
correspond to the final conditions. For df1
, df1t
, df1sos
and df1tsos
structures, states
returns
a filtstate
object.
PersistentMemory
— controls
whether filter states
are saved. The default value
is 'false'
, which causes the initial conditions
to be reset to zero before filtering and turns off the display of states
information.
Setting PersistentMemory
to 'true'
allows
the filter to use your initial conditions or to reuse the final conditions
of a previous filtering operation as the initial conditions of the
next filtering operation. It also displays information about the
filter states
.
Note
If you set |
Create a direct-form I filter and use a method to see if it is stable.
[b,a] = butter(8,0.25); Hd = dfilt.df1(b,a)
If a dfilt
's numerator values do not fit
on a single line, a description of the vector is displayed. To see
the specific numerator values for this example, use
get(Hd,'numerator')
or alternatively
Hd.numerator
Refer to the reference pages for each structure for more examples.
dfilt.cascade
| dfilt.df1
| dfilt.df1t
| dfilt.df2
| dfilt.df2t
| dfilt.dfasymfir
| dfilt.dffir
| dfilt.dffirt
| dfilt.dfsymfir
| dfilt.latticeallpass
| dfilt.latticear
| dfilt.latticearma
| dfilt.latticemamax
| dfilt.latticemamin
| dfilt.parallel
| dfilt.statespace
| filter
| freqz
| grpdelay
| impz
| step
| tf
| zpk
| zplane