fircband (Digital Filter Design Toolkit, MathScript Function)
Owning Class: singlerate
Syntax
b = fircband(n, f, mag, w, c)
b = fircband(n, f, mag, w, c, t)
b = fircband(n, f, mag, ftype)
b = fircband(n, f, mag, ftype, t)
Description
Designs a finite impulse response (FIR) filter with constraints in the frequency bands by using the minimax principle. The FIR filter minimizes the maximum error between the target frequency response and the designed filter frequency response. You can use this function to design the following FIR filters: types IIV linear phase, minimum and maximum phase, ripple constraint, singlepoint band, exact gain control, and arbitrary shape.
Inputs
Name  Description  
n  Specifies the order of the filter. n is a nonnegative integer.  
f  Specifies the frequency points. f is a vector whose values increase monotonically between 0 and 1.  
mag  Specifies the magnitude response of the filter at f. mag is a vector with the same length as f.  
w  Specifies the weight of each frequency band. w is a vector whose length must equal length(f)/2.  
c  Specifies whether each element of w is a weight or a ripple constraint of a frequency band. c is a string of the same length as w that accepts a combination of the following values:


t  Specifies the type of filter you want to design. t is a string that accepts the following values:


ftype  Specifies the type of each frequency point in f. ftype is a string of the same length as f that accepts a combination of the following values:

Outputs
Name  Description 
b  Returns the coefficients of the designed FIR filter. b is a real vector with a length of n+1. 
Examples
b = fircband(22, [0, 0.4, 0.5, 0.7, 0.8, 1], [1, 1, 0, 0, 1, 1], [0.05, 1, 0.1], 'cwc');
fft_mag = abs(fft(b, 16384));
figure;
plot(0:1/8192:1, fft_mag(1:8193));
b = fircband(42, [0, 0.2, 0.25, 0.3, 0.5, 0.55, 0.6, 1], [1, 1, 0, 1, 1, 0, 1, 1], 'nnsnnsnn');
fft_mag = abs(fft(b, 16384));
figure;
plot(0:1/8192:1, fft_mag(1:8193));
b = fircband(82, [0, 0.0055, 0.03, 0.1, 0.15, 1], [0, 0, 0, 0, 1, 1], 'nnennn');
fft_mag = abs(fft(b, 16384));
figure;
plot(0:1/8192:1, fft_mag(1:8193));
b = fircband(12, [0, 0.4, 0.5, 1], [1, 1, 0, 0], [1, 1], 'ww', 'minphase');
fft_mag = abs(fft(b, 16384));
figure;
plot(0:1/8192:1, fft_mag(1:8193));
figure;
zplane(b, 1);