Transform FIR Type I lowpass to FIR Type 1 lowpass with inverse bandwidth
b is a narrowband filter,
g will be a
wideband filter and vice versa. The passband and stopband ripples of
g will be equal to the stopband and passband ripples of
Convert Narrowband Lowpass Filter to Wideband Lowpass Filter
Create a narrowband lowpass filter to use as a 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
b — Lowpass FIR filter coefficients
Type 1 lowpass FIR filter coefficients with zero-phase response Hr(w), specified as a row vector.
g — Transformed lowpass FIR filter coefficients
Transformed Type 1 lowpass FIR filter coefficients with zero-phase response 1-Hr(pi-w), specified as a row vector.
 Mitra, Sanjit Kumar, and James F. Kaiser, eds. Handbook for Digital Signal Processing. New York: Wiley, 1993.