Signal Toolkit - fir2

Function File: b = fir2 (n, f, m)

Function File: b = fir2 (n, f, m, grid_n)

Function File: b = fir2 (n, f, m, grid_n, ramp_n)

Function File: b = fir2 (n, f, m, grid_n, ramp_n, window)

Produce an order n FIR filter with arbitrary frequency response m over frequency bands f, returning the n+1 filter coefficients in b. The vector f specifies the frequency band edges of the filter response and m specifies the magnitude response at each frequency.

The vector f must be nondecreasing over the range [0,1], and the first and last elements must be 0 and 1, respectively. A discontinuous jump in the frequency response can be specified by duplicating a band edge in f with different values in m.

The resolution over which the frequency response is evaluated can be controlled with the grid_n argument. The default is 512 or the next larger power of 2 greater than the filter length.

The band transition width for discontinuities can be controlled with the ramp_n argument. The default is grid_n/25. Larger values will result in wider band transitions but better stopband rejection.

An optional shaping window can be given as a vector with length n+1. If not specified, a Hamming window of length n+1 is used.

To apply the filter, use the return vector b with the filter function, for example y = filter (b, 1, x).

Example:

 f = [0, 0.3, 0.3, 0.6, 0.6, 1]; m = [0, 0, 1, 1/2, 0, 0];
 [h, w] = freqz (fir2 (100, f, m));
 plot (f, m, ";target response;", w/pi, abs (h), ";filter response;");
 

See also: filter, fir1.