b = remez(n, f, a [, w] [, ftype] [, griddensity])
Parks-McClellan optimal FIR filter design.
n gives the number of taps in the returned filter
f gives frequency at the band edges [ b1 e1 b2 e2 b3 e3 ...]
a gives amplitude at the band edges [ a(b1) a(e1) a(b2) a(e2) ...]
w gives weighting applied to each band
ftype is 'bandpass', 'hilbert' or 'differentiator'
griddensity determines how accurately the filter will be
    constructed. The minimum value is 16, but higher numbers are
    slower to compute.

Frequency is in the range (0, 1), with 1 being the nyquist frequency