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firtype

Type of linear phase FIR filter

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Syntax

t = firtype(b)
t = firtype(d)

Description

t = firtype(b) determines the type, t, of an FIR filter. Specify the filter coefficients with a vector 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.

example

Examples

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Open Live Script

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))])

Figure contains 2 axes objects. Axes object 1 with title Type 1, xlabel n (samples), ylabel Amplitude contains an object of type stem. Axes object 2 with title Type 2, xlabel n (samples), ylabel Amplitude contains an object of type stem.

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))])

Figure contains 2 axes objects. Axes object 1 with title Type 3, xlabel n (samples), ylabel Amplitude contains an object of type stem. Axes object 2 with title Type 4, xlabel n (samples), ylabel Amplitude contains an object of type stem.

Open Live Script

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

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

Version History

Introduced in R2013a

See Also

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