Convert FIR Type I lowpass to FIR Type 1 lowpass with inverse bandwidth
g = firlp2lp(b)
g = firlp2lp(b) transforms
the Type I lowpass FIR filter
b with zero-phase
response Hr(w) to a Type I lowpass FIR filter
zero-phase response [1 - Hr(π-w)].
b is a narrowband filter,
be a wideband filter and vice versa. The passband and stopband ripples
g will be equal to the stopband and passband
Create a narrowband lowpass filter to use as prototype. Display its zero-phase response.
b = firgr(36,[0 0.2 0.25 1],[1 1 0 0],[1 5]); zerophase(b)
Convert the prototype filter to a wideband lowpass filter. Add to the plot the zero-phase response of the new filter.
h = firlp2lp(b); hold on zerophase(h)
Convert the previous filter back to a narrowband lowpass filter. Add to the plot the zero-phase response of the new filter.
g = firlp2lp(h); [gr,w] = zerophase(g); plot(w/pi,gr,'--') hold off
Saramaki, T, Finite Impulse Response Filter Design, Handbook for Digital Signal Processing. S.K. Mitra and J.F. Kaiser Eds. Wiley-Interscience, N.Y., 1993, Chapter 4.