Lanczos notch

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

Lanczos 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

# A lowpass at 0 is sinc(x)

ls = [(sinc(x * 5/36) - sinc(x * 7/36) + sinc(x * 10/36))
      * sinc(x/21)
      for x in range(-20, 21)]
print "\n".join("%7.4f" % el for el in ls)