Blackman notch

#!/usr/bin/env python
"""

Blackman dual-passband filter generator
by Damian Yerrick

Bisqwit wanted help making the FIR filter for NTSC luma/chroma
separation.  I'm using a crossover at 5/6 and 7/6 Fsc (3.0 and
4.2 MHz).

"""
from __future__ import division
import math

def sinc(x):
    pix = math.pi*x
    return math.sin(pix)/pix if pix else 1

# Sum of a lowpass and a bandpass
ls = [(sinc(x * 5/36) - sinc(x * 7/36) + sinc(x * 10/36))
      * 1
      for x in range(-35, 36)]

# Apply Blackman window
N = len(ls)
alpha = 0.16
black = [(1 - alpha - math.cos(2*math.pi*x/(N+1))
          + alpha*math.cos(4*math.pi*x/(N+1)))/2
         for x in range(1, N+1)]
ls = [a * b for (a, b) in zip(black, ls)]

print "Filter: [%s]" % ",".join("%7.4f" % el for el in ls)
print "DC convolve: %.4f" % sum(ls)
sineconv = [sum(math.cos(math.pi*(x + i)/6) * y
                for (x, y) in zip(range(len(ls)), ls))
            for i in range(12)]
print "Sine convolve (wanna get these values compared to DC convolve):"
print "[%s]" % ",".join("%7.4f" % el for el in sineconv)