ref: ca5618deb1a747f3b46f6240a2b232e632c37b0e
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