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mfilt.iirwdfinterp

IIR wave digital filter interpolator

Syntax

hm = mfilt.iirwdfinterp(c1,c2,...)

Description

hm = mfilt.iirwdfinterp(c1,c2,...) constructs an IIR wave digital interpolator given the coefficients specified in the cell arrays c1, c2, and so on. The IIR interpolator hm is a polyphase IIR filter where each phase is a cascade wave digital 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.cascadewdfallpass. The contents of the cell arrays are the same for both filter constructors and mfilt.iirwdfinterp interprets them same way as mfilt.cascadewdfallpass.

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 one element equal to 1, that cell array represents a dfilt.delay section with latency equal to the number of zeros, rather than a dfilt.cascadewdfallpass section. This exception occurs with quasi-linear phase IIR interpolators.

Usually you do not construct IIR wave digital filter interpolators explicitly. Rather, you obtain an IIR wave digital interpolator as a result of designing a halfband interpolator. The first example in the following section illustrates this case.

Examples

Design an elliptic halfband interpolator with interpolation factor equal to 2. At the end of the design process, hm is an IIR wave digital filter interpolator.

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

The specification object d stores the interpolator design requirements. Now use d to design the actual filter hm.

hm = design(d,'ellip','filterstructure','iirwdfinterp');

If you have Simulink® installed, you can realize your filter as a model built from DSP System Toolbox™ blocks.

% Note that realizemdl requires Simulink
realizemdl(hm)     % Build model of the filter.

For variety, design a linear phase halfband interpolator with an interpolation factor of 2.

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

Now perform the actual design process with d. Filter hm is an IIR wave digital filter interpolator. As in the previous example, realizemdl returns a Simulink model of the filter if you have Simulink installed.

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

See Also

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