Re: [Discuss-gnuradio] notch filter

[Chuck Swiger]

Here's the final working notch filter script -

notch.py
----------------------------------------------------------
#!/usr/bin/env python
#
# Copyright 2004 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2, or (at your option)
# any later version.
#
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING.  If not, write to
# the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
# Boston, MA 02111-1307, USA.
#

import sys
from gnuradio import gr
from gnuradio import audio

def build_graph (freq):
    sampling_freq = 48000

    fg = gr.flow_graph ()

    # notch filter frequency = ( 1 / ( delays * unit_delay ) ) / 2
    # where unit_delay = 20.8333 uSec for 48000 sampling rate

    nd = (int) ( .5 + ( 1 / ( 2 * freq * 20.8333e-6 ) ) )
    print "Exact notch freq = ",( 1 / ( nd * 20.8333e-6 * 2 ) )

    taps = [1]
    for i in range(1,nd):
       taps = taps + [0]
    taps = taps + [1]

    src0 = audio.source (sampling_freq)

    notch = gr.fir_filter_fff (1, taps)

    scale = gr.multiply_const_ff (.5)
    dst = audio.sink (sampling_freq)

    fg.connect (src0, notch)
    fg.connect (notch, scale)
    fg.connect (scale, dst)

    return fg

def main (args):
    nargs = len (args)
    if nargs == 1:
       freq = float (args[0])
    else:
       sys.stderr.write ('usage: notch.py freq\n')
       sys.exit (1)

    fg = build_graph (freq)
    fg.start ()
    raw_input ('Press Enter to quit: ')
    fg.stop ()

if __name__ == '__main__':
    main (sys.argv[1:])