firls

Create a digital FIR multi-band filter with a least squares fitting.

Syntax

[b] = firls(n,f,a)

[b] = firls(n,f,a,w)

Inputs

n
The filter order.
The order is an even integer.
Type: integer
Dimension: scalar
f
A vector specifying the frequency band edges. The frequencies are normalized so that the Nyquist frequency is 1.
Type: double
Dimension: vector
a
A vector specifying the amplitude at each frequency band edge.
Type: double
Dimension: vector
w
A vector specifying weights, with one weight per band. The default is an unweighted fit.
Type: double
Dimension: vector

Outputs

b
The polynomial coefficients of the filter.
Type: vector

Example

Plot the magnitude response for a 20th order FIR digital filter with a stop band from 200 to 250 Hz that is weighted twice as much as the pass bands, and a 1000 Hz sampling frequency.
fs = 1000;
f = [0, 100, 200, 250, 350, 490];
a = [1,1,0,0,1,1];
w = [1,2,1];
b = firls(20, f/(fs/2), a, w);
[h,f] = freqz(b,1,[0:5:500],fs);
plot(f,abs(h));