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firtype

Type of linear phase FIR filter

Description

example

t = firtype(b) determines the type, t, of an FIR filter with coefficients b. t can be 1, 2, 3, or 4. The filter must be real and have linear phase.

example

t = firtype(d) determines the type, t, of an FIR filter, d. t can be 1, 2, 3, or 4. The filter must be real and have linear phase.

Examples

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Design two FIR filters using the window method, one of even order and the other of odd order. Determine their types and plot their impulse responses.

subplot(2,1,1)
b = fir1(8,0.5);
impz(b), title(['Type ' int2str(firtype(b))])

subplot(2,1,2)
b = fir1(9,0.5);
impz(b), title(['Type ' int2str(firtype(b))]) Design two equiripple Hilbert transformers, one of even order and the other of odd order. Determine their types and plot their impulse responses.

subplot(2,1,1)
b = firpm(8,[0.2 0.8],[1 1],'hilbert');
impz(b), title(['Type ' int2str(firtype(b))])

subplot(2,1,2)
b = firpm(9,[0.2 0.8],[1 1],'hilbert');
impz(b), title(['Type ' int2str(firtype(b))]) Use designfilt to design the filters from the previous example. Display their types.

d1 = designfilt('lowpassfir','DesignMethod','window', ...
'FilterOrder',8,'CutoffFrequency',0.5);
disp(['d1 is of type ' int2str(firtype(d1))])
d1 is of type 1
d2 = designfilt('lowpassfir','DesignMethod','window', ...
'FilterOrder',9,'CutoffFrequency',0.5);
disp(['d2 is of type ' int2str(firtype(d2))])
d2 is of type 2
d3 = designfilt('hilbertfir','DesignMethod','equiripple', ...
'FilterOrder',8,'TransitionWidth',0.4);
disp(['d3 is of type ' int2str(firtype(d3))])
d3 is of type 3
d4 = designfilt('hilbertfir','DesignMethod','equiripple', ...
'FilterOrder',9,'TransitionWidth',0.4);
disp(['d4 is of type ' int2str(firtype(d4))])
d4 is of type 4

Input Arguments

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Filter coefficients of the FIR filter, specified as a double- or single-precision real-valued row or column vector.

Data Types: double | single

FIR filter, specified as any of the following:

• A digitalFilter object. Use designfilt to generate a digital filter based on frequency-response specifications.

• A dfilt filter object.

Output Arguments

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Filter type, returned as either 1, 2, 3, or 4. Filter types are defined as follows:

• Type 1 — Even-order symmetric coefficients

• Type 2 — Odd-order symmetric coefficients

• Type 3 — Even-order antisymmetric coefficients

• Type 4 — Odd-order antisymmetric coefficients