Cascade of allpass discrete-time filters
hd = dfilt.cascadeallpass(c1,c2,...)
hd = dfilt.cascadeallpass(c1,c2,...) constructs
a cascade of allpass filters, each of which uses the minimum number
of multipliers, given the filter coefficients provided in
and so on.
c represents one section in the
c vectors must contain one, two,
three, or four elements as the filter coefficients for each section.
As a result of the design algorithm, each section is a
dfilt.allpass structure whose coefficients
are given in the matching
c vector, such as the
contains the coefficients for the first stage.
States for each section are shared between sections.
c do not have to be the same length.
You can combine various length vectors in the input arguments. For
example, you can cascade fourth-order sections with second-order sections,
or first-order sections.
For more information about the vectors
about the transfer function of each section, refer to
Generally, you do not construct these allpass cascade filters
directly. Instead, they result from the design process for an IIR
filter. Refer to the first example in Examples for more about using
design an IIR filter.
In the next table, the row entries are the filter properties and a brief description of each property.
Contains the coefficients for the allpass filter object
Describes the signal flow for the filter object, including all of the active elements that perform operations during filtering — gains, delays, sums, products, and input/output.
Specifies whether to reset the filter states and memory
before each filtering operation. Lets you decide whether your filter
retains states from previous filtering runs.
This property contains the filter states before, during,
and after filter operations. States act as filter memory between filtering
runs or sessions. They also provide linkage between the sections of
a multisection filter, such as a cascade filter. For details, refer
Two examples show how
in very different applications — designing a halfband IIR filter
and constructing an allpass cascade of
First, design the IIR halfband filter using cascaded allpass filters. Each branch of the parallel cascade construction is a cascadeallpass filter object.
tw = 100; % Transition width of filter to be designed, 100 Hz. ast = 80; % Stopband attenuation of filter to be designed, 80dB. fs = 2000; % Sampling frequency of signal to be filtered. % Store halfband design specs in the specifications object d. d = fdesign.halfband('tw,ast',tw,ast,fs);
Now perform the actual filter design.
hd = design(d,'ellip','filterstructure','cascadeallpass'); % Get summary information about one dfilt.cascadeallpass stage. StageInfo = hd.Stage(1).Stage(1);
This second example constructs a
object directly given allpass coefficients for the input vectors.
section1 = 0.8; section2 = [1.2,0.7]; section3 = [1.3,0.9]; hd = dfilt.cascadeallpass(section1,section2,section3); % Get information about the filter % return informatio in character array S = info(hd);