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freqsamp

Real or complex frequency-sampled FIR filter from specification object

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Syntax

hd = design(d,'freqsamp','SystemObject',true)
hd = design(...,'filterstructure',structure,'SystemObject',true)
hd = design(...,'window',window,'SystemObject',true)

Description

hd = design(d,'freqsamp','SystemObject',true)designs a frequency-sampled filter specified by the filter specifications objectd．

hd = design(...,'filterstructure',structure,'SystemObject',true)returns a filter with the filter structure you specify by thestructureinput argument.structureisdffirby default and can be any one of the following filter structures.

Structure

Description of Resulting Filter Structure

dffir

Direct-form FIR filter

dffirt

Transposed direct-form FIR filter

dfsymfir

对称的直接形式冷杉过滤器

dfasymfir

Asymmetrical direct-form FIR filter

hd = design(...,'window',window,'SystemObject',true)designs filters using the window specified bywindow．Provide the input argumentwindowas

  • A character vector for the window type. For example, use'bartlett', or'hamming'．看到windowfor the full list of windows available.

  • A function handle that references thewindowfunction. When thewindowfunction requires more than one input, use a cell array to hold the required arguments. The first example shows a cell array input argument.

  • The window vector itself.

Examples

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These examples design FIR filters that have arbitrary magnitude responses. In the first filter, the response has three distinct sections and the resulting filter is real.

The second example creates a complex filter.

b1 = 0:0.01:0.18;b2 =[。2。38 .4 .55 .562 .585 .6 .78]; b3 = 0.79:0.01:1; a1 = .5+sin(2*pi*7.5*b1)/4;% Sinusoidal response section.a2 = [.5 2.3 1 1 -.2 -.2 1 1];% Piecewise linear response section.a3 = .2+18*(1-b3).^2;% Quadratic response section.f = [b1 b2 b3]; a = [a1 a2 a3]; n = 300; d = fdesign.arbmag('n,f,a',n,f,a);% First specifications object.hd = design(d,'freqsamp','window',{@kaiser,.5},．..'SystemObject',true);% Filter.fvtool(hd)

Figure Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB) contains 2 objects of type line.

Now design the arbitrary-magnitude complex FIR filter. Recall that vector f contains frequency locations and vector a contains the desired filter response values at the locations specified in f.

f = [-1 -.93443 -.86885 -.80328 -.7377 -.67213 -.60656 -.54098．..-。47541,-.40984 -.34426 -.27869 -.21311 -.14754 -.081967．..-。016393 .04918 .11475,.18033 .2459 .31148 .37705 .44262．..．5082 .57377 .63934 .70492 .77049,.83607 .90164 1]; a = [.0095848 .021972 .047249 .099869 .23119 .57569 .94032．..．98084 .99707,.99565 .9958 .99899 .99402 .99978 .99995 .99733．..．99731 .96979 .94936,.8196 .28502 .065469 .0044517 .018164．..．023305 .02397 .023141 .021341,.019364 .017379 .016061]; n = 48; d = fdesign.arbmag('n,f,a',n,f,a);% Second spec. object.hdc = design(d,'freqsamp','window','rectwin','SystemObject',true);% Filter.fvtool(hdc)

Figure Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB) contains 2 objects of type line.

fvtool shows you the response for hdc from -1 to 1 in normalized frequency. design(d,...) returns a complex filter for hdc because the frequency vector includes negative frequency values.

Version History

Introduced in R2011a

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