mfilt

(To be removed) Multirate filter

Compatibility

mfilt will be removed in a future release. See dsp.CICDecimator, dsp.CICInterpolator, dsp.FIRDecimator, dsp.FIRInterpolator, dsp.FilterCascade, dsp.FarrowRateConverter, dsp.FIRRateConverter, dsp.IIRHalfbandDecimator, or dsp.IIRHalfbandInterpolator instead.

Syntax

hm = mfilt.structure(input1,input2,...)

Description

hm = mfilt.structure(input1,input2,...) returns the object hm of type structure. As with dfilt objects, you must include the structure to construct a multirate filter object. You can, however, construct a default multirate filter object of a given structure by not including input arguments in your calling syntax.

Multirate filters include decimators and interpolators, and fractional decimators and fractional interpolators where the resulting interpolation or decimation factor is not an integer.

Structures

Each of the following multirate filter structures has a reference page of its own.

Filter Structure	Description of Resulting Multirate Filter	Coefficient Mapping Support in `realizemdl`
`mfilt.cascade`	Cascade multirate filters to form another filter	Supported
`mfilt.cicdecim`	Cascaded integrator-comb decimator	Not supported
`mfilt.cicinterp`	Cascaded integrator-comb interpolator	Not supported
`mfilt.farrowsrc`	Multirate Farrow filter	Supported.
`mfilt.fftfirinterp`	Overlap-add FIR polyphase interpolator	Not supported
`mfilt.firdecim`	Direct-form FIR polyphase decimator	Supported
`mfilt.firinterp`	Direct-form FIR polyphase interpolator	Supported
`mfilt.firsrc`	Direct-form FIR polyphase sample rate converter	Supported
`mfilt.firtdecim`	Direct-form transposed FIR polyphase decimator	Supported
`mfilt.holdinterp`	FIR hold interpolator	Not supported
`mfilt.iirdecim`	IIR decimator	Supported
`mfilt.iirinterp`	IIR interpolator	Supported
`mfilt.linearinterp`	FIR Linear interpolator	Supported
`mfilt.iirwdfdecim`	IIR wave digital filter decimator	Supported
`mfilt.iirwdfinterp`	IIR wave digital filter interpolator	Supported

Copying mfilt Objects

To create a copy of an mfilt object, use the copy method.

h2 = copy(hd)

Note

The syntax hd2 = hd copies only the object handle. It does not create a new object. hd2 and hd are not independent. If you change the property value for one of the two, such as hd2, you are changing the property for both.

Examples

Decimation by a factor of two. Convert input sampled at 48 kHz to 24 kHz:

Fs = 4.8e4;
t =0:1/Fs:1-(1/Fs);
x = cos(2*pi*4000*t);
Hm=mfilt.firdecim(2);
% Note cutoff frequency of 1/2 normalized frequency
fvtool(Hm);
% Note the group delay of 34 samples
fvtool(Hm,'analysis','grpdelay');
y = filter(Hm,x);
% Note delay in output is consistent with 36/2
stem(y(1:48),'markerfacecolor',[0 0 1]);

Using existing coefficients to decimate a signal by a factor of two:

		 M = 2; % Decimation factor
     b = firhalfband('minorder',.45,0.0001);
     Hm = mfilt.firdecim(M,b);
     % Decimate a signal which consists of the sum of 2 sinusoids.
     N = 160;
     x = sin(2*pi*.05*[0:N-1]+pi/3)+cos(2*pi*.03*[0:N-1]+pi/3);
     y = filter(Hm,x);

Note

Multirate filters can also have complex coefficients. For example, you can specify complex coefficients in the argument num passed to the filter structure. This works for all multirate filter structures.

m = 2;
num = [0.5 0.5+1j*0.2];
Hm = mfilt.firdecim(m, num);
y = filter(Hm, [1:10]);

Version History

Introduced in R2011a