ref: 06a021bb7ab5a85975a6e27b7cc5255768df3666
dir: /Octave/make_filter.m/
function f = make_filter (cycles, increment, atten, filename)
# This works :
#
# f = make_filter (67, 128, 100.3) ;
# f = make_filter (13, 128, 100.5) ;
# f = make_filter (185, 4, 157.0) ;
#=======================================================================
if nargin < 3,
error ('Try make_filter (12, 32, 88, "output.txt")') ;
endif
if nargin < 4,
filename = 0 ;
elseif (isstr (filename) == 0),
error ("Fourth parameter must be a file name.") ;
endif
fudge_factor1 = 1.0 ;
f1 = generate_filter (cycles, fudge_factor1, increment, atten) ;
[stop_atten stop_band_start1 minus_3db] = measure_filter (f1, atten) ;
printf (" fudge_factor : %15.13f stop_band_start : %15.13f 1\n", fudge_factor1, stop_band_start1) ;
fudge_factor2 = 1.25 ;
f2 = generate_filter (cycles, fudge_factor2, increment, atten) ;
[stop_atten stop_band_start2 minus_3db] = measure_filter (f2, atten) ;
printf (" fudge_factor : %15.13f stop_band_start : %15.13f 2\n", fudge_factor2, stop_band_start2) ;
f = f1 ;
fudge_factor = fudge_factor1 ;
stop_band_start = stop_band_start1 ;
while ((stop_band_start1 - stop_band_start2) > 0.0000000001)
if (stop_band_start1 < stop_band_start2)
printf ("stop_band_start1 < stop_band_start2\n") ;
break ;
endif
fudge_factor = fudge_factor1 + (fudge_factor2 - fudge_factor1) / 2 ;
f = generate_filter (cycles, fudge_factor, increment, atten) ;
[stop_atten stop_band_start minus_3db] = measure_filter (f, atten) ;
if (stop_band_start > 1.0)
printf ("A %10.8f %10.8f %10.8f\n", fudge_factor1, fudge_factor, fudge_factor2) ;
continue ;
endif
if (stop_band_start < 0.5 / increment)
f2 = f ;
stop_band_start2 = stop_band_start ;
fudge_factor2 = fudge_factor ;
choice = 2 ;
else
f1 = f ;
stop_band_start1 = stop_band_start ;
fudge_factor1 = fudge_factor ;
choice = 1 ;
endif
printf (" fudge_factor : %15.13f stop_band_start : %15.13f %d\n", fudge_factor, stop_band_start, choice) ;
endwhile
printf ("\n") ;
#-------------------------------------------------------------------------------
# Grab only half the coefficients.
N = length (f) ;
f = increment * f' ;
if rem (length (f), 2) == 0,
index = find (f == max (f)) ;
index = min (index) - 1 ;
half_f = f (index:length (f)) ;
else
error ("Length should be even.") ;
endif
trailing_zeros = 4 - rem (length (half_f), 4) ;
#-------------------------------------------------------------------------------
# Print analysis.
printf ("# f = make_filter (%d, %d, %4.1f) ;\n", cycles, increment, atten) ;
printf ("# Coeff. count : %d\n", N) ;
printf ("# Fudge factor : %9.7f\n", fudge_factor) ;
printf ("# Pass band width : %12.10f (should be %12.10f)\n", stop_band_start, 0.5 / increment) ;
printf ("# Stop band atten. : %5.2f dB\n", abs (stop_atten)) ;
printf ("# -3dB band Width : %5.3f\n", 0.5 / increment / minus_3db) ;
printf ("# half length : %d\n", length (half_f) + trailing_zeros) ;
printf ("# increment : %d\n", increment) ;
if filename,
file = fopen (filename, "w") ;
if file == 0,
str = sprintf ("Error, not able to open '%s'", filename)
error (str) ;
endif
fprintf (file, "/*\n") ;
fprintf (file, "** f = make_filter (%d, %d, %4.1f) ;\n", cycles, increment, atten) ;
fprintf (file, "** Pass band width : %9.7f (should be %9.7f)\n", stop_band_start, 0.5 / increment) ;
fprintf (file, "** Stop band atten. : %5.2f dB\n", abs (stop_atten)) ;
fprintf (file, "** -3dB band width : %5.3f\n", 0.5 / increment / minus_3db) ;
fprintf (file, "** half length : %d\n", length (half_f)) ;
fprintf (file, "** increment : %d\n", increment) ;
fprintf (file, "*/\n\n") ;
for val = half_f,
fprintf (file, "% 24.20e,\n", val) ;
endfor
if trailing_zeros > 0,
for val = 2:trailing_zeros,
fprintf (file, " 0,\n") ;
endfor
fprintf (file, " 0\n") ;
endif
fclose (file) ;
endif
endfunction
# Do not edit or modify anything in this comment block.
# The arch-tag line is a file identity tag for the GNU Arch
# revision control system.
#
# arch-tag: 2f1ff4fa-ea6a-4e54-a5f8-dad55def9834