IIR interpolator

`hm = mfilt.iirinterp(c1,c2,...)`

`hm = mfilt.iirinterp(c1,c2,...)`

constructs
an IIR interpolator filter given the coefficients specified in the
cell arrays C1, C2, etc.

The IIR interpolator is a polyphase IIR filter where each phase is a cascade allpass IIR filter.

Each cell array `ci`

contains a set of vectors
representing a cascade of allpass sections. Each element in one cell
array is one section. For more information about the contents of each
cell array, refer to `dfilt.cascadeallpass`

.
The contents of the cell arrays are the same for both filter constructors
and `mfilt.iirdecim`

interprets them same way as `mfilt.cascadeallpass`

.

The following exception applies to interpreting the contents
of a cell array—if one of the cell arrays `ci`

contains
only one vector, and that vector comprises a series of 0s and a unique
element equal to 1, that cell array represents a `dfilt.delay`

section with latency equal
to the number of zeros, rather than a `dfilt.cascadeallpass`

section.
This exception case occurs with quasi-linear phase IIR interpolators.

Although the first example shows how to construct an IIR interpolator explicitly, one usually constructs an IIR interpolator filter as a result of designing an interpolator, as shown in the subsequent examples.

When the coefficients are known, you can construct the IIR interpolator
directly using `mfilt.iirinterp`

. In the following
example, a cascaded polyphase IIR interpolator filter is constructed
using 2 phases for each of three stages. The coefficients are given
below:

Phase1Sect1=0.0603;Phase1Sect2=0.4126; Phase1Sect3=0.7727; Phase2Sect1=0.2160; Phase2Sect2=0.6044; Phase2Sect3=0.9239;

Next the filter is implemented by passing the above coefficients
to `mfilt.iirinterp`

as cell arrays, where each cell
array represents a different phase.

Hm = mfilt.iirinterp({Phase1Sect1,Phase1Sect2,Phase1Sect3},... {Phase2Sect1,Phase2Sect2,Phase2Sect3}) Hm = FilterStructure: 'IIR Polyphase Interpolator' Polyphase: Phase1: Section1: 0.0603 Section2: 0.4126 Section3: 0.7727 Phase2: Section1: 0.216 Section2: 0.6044 Section3: 0.9239 InterpolationFactor: 2 PersistentMemory: false

Also refer to the "Quasi-Linear Phase Halfband and Dyadic Halfband Designs" section of the "IIR Polyphase Filter Design" example, iirallpassdemoiirallpassdemo example.

When the coefficients are not known, use the approach given by the following set of examples. Start by designing an elliptic halfband interpolator with a interpolation factor of 2.

tw = 100; % Transition width of filter. ast = 80; % Stopband attenuation of filter. fs = 2000; % Sampling frequency of filter. l = 2; % Interpolation factor. d = fdesign.interpolator(l,'halfband','tw,ast',tw,ast,fs);

Specification object `d`

stores the interpolator
design specifics. With the details in `d`

, design
the filter, returning `hm`

, an `mfilt.iirinterp`

object.
Use `hm`

to realize the filter if you have Simulink^{®} installed.

hm = design(d,'ellip','filterstructure','iirinterp'); % Note that realizemdl requires Simulink realizemdl(hm) % Build model of the filter.

Designing a linear phase halfband interpolator follows the same pattern.

tw = 100; % Transition width of filter. ast= 60; % Stopband attenuation of filter. fs = 2000; % Sampling frequency of filter. l = 2; % Interpolation factor. d = fdesign.interpolator(l,'halfband','tw,ast',tw,ast,fs);

`fdesign.interpolator`

returns
a specification object that stores the design features for an interpolator.

Now perform the actual design that results in an `mfilt.iirinterp`

filter, `hm`

.

hm = design(d,'iirlinphase','filterstructure','iirinterp'); % Note that realizemdl requires Simulink realizemdl(hm) % Build model of the filter.

The toolbox creates a Simulink model for `hm`

,
shown here. Phase1, Phase2, and InterpCommutator are all subsystem
blocks.

For more information about Multirate Filter Constructors see the "Getting Started with Multirate Filter (MFILT) Objects" example, mfiltgettingstarteddemomfiltgettingstarteddemo.

`dfilt.cascadeallpass`

| `mfilt`

| `mfilt.iirdecim`

| `mfilt.iirwdfinterp`

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