Add Octave scripts to generate filter coefficients

Erik de Castro Lopo committed 7 years ago

Commit 29b0b171 parent d1054fb5 files · +269 −1Browse files

Unified · Split

5 files

Makefile.am +3 −1
Octave/Readme.md +27 −0
Octave/generate_filter.m +35 −0
Octave/make_filter.m +134 −0
Octave/measure_filter.m +70 −0

@@ -4,7 +4,9 @@ DISTCHECK_CONFIGURE_FLAGS = --enable-werror · 3 unmodified lines
4	4
5	5	AM_CPPFLAGS = -I$(top_srcdir)/src $(OS_SPECIFIC_INCLUDES)
6	6
7		−EXTRA_DIST = autogen.sh libsamplerate.spec.in samplerate.pc.in Make.bat Win32
	7	+EXTRA_DIST = autogen.sh libsamplerate.spec.in samplerate.pc.in Make.bat Win32 \
	8	+ Octave/generate_filter.m Octave/make_filter.m Octave/measure_filter.m \
	9	+ Octave/Readme.md
8	10
9	11	pkgconfig_DATA = samplerate.pc
10	12

Octave/Readme.md+27−0

@@ -0,0 +1,27 @@
	1	+# Gneerating Filter Coefficients
	2	+
	3	+The scripts below are used in [GNU Octave][GNU Octave] which should be available
	4	+on most platforms including Linux, Mac and Windows.
	5	+
	6	+On Debian and other Debian derived Linux distributions, Octave can be installed
	7	+using: `sudo apt install octave octave-signal`.
	8	+
	9	+Filter coefficients can be generated as follows by running the `octave` command
	10	+in the same directory as the scripts and this Readme file:
	11	+
	12	+```
	13	+octave:1> pkg load signal
	14	+octave:2> f = make_filter (8, 128, 100.3) ;
	15	+# f = make_fip_filter (8, 128, 100.3) ;
	16	+# Coeff. count : 4922
	17	+# Fudge factor : 1.2018769
	18	+# Pass band width : 0.0039062499 (should be 0.0039062500)
	19	+# Stop band atten. : 100.71 dB
	20	+# -3dB band Width : 0.490
	21	+# half length : 2464
	22	+# increment : 128
	23	+```
	24	+
	25	+The parameters above generate the coefficient set used in `src/fastest_coeffs.h`.
	26	+
	27	+[GNU Octave]: https://www.gnu.org/software/octave/

Octave/generate_filter.m+35−0

@@ -0,0 +1,35 @@
	1	+function f = generate_filter (cycles, fudge_factor, increment, atten)
	2	+
	3	+if nargin != 4,
	4	+ error ("Need four args.") ;
	5	+ endif
	6	+
	7	+# Calclate N and make sure it is even.
	8	+N = fix (4 * cycles * fudge_factor * increment) ;
	9	+
	10	+if rem (N, 2) != 0,
	11	+ N = N - 1 ;
	12	+ endif
	13	+
	14	+# Generate the Sinc function.
	15	+
	16	+m = -((N-1)/2):((N-1)/2) ;
	17	+f = sinc (m / fudge_factor / increment) ;
	18	+
	19	+# Genertate the window function and apply it.
	20	+
	21	+w = kaiser (N, (atten + 0.5) / 10) ;
	22	+w = w' ;
	23	+
	24	+f = f .* w ;
	25	+
	26	+f = f / sum (f) ;
	27	+
	28	+endfunction
	29	+
	30	+# Do not edit or modify anything in this comment block.
	31	+# The arch-tag line is a file identity tag for the GNU Arch
	32	+# revision control system.
	33	+#
	34	+# arch-tag: 7e57a3cb-3f5c-4346-bfcd-4da1e758e2a7
	35	+

Octave/make_filter.m+134−0

@@ -0,0 +1,134 @@
	1	+function f = make_filter (cycles, increment, atten, filename)
	2	+
	3	+# This works :
	4	+#
	5	+# f = make_filter (67, 128, 100.3) ;
	6	+# f = make_filter (13, 128, 100.5) ;
	7	+# f = make_filter (185, 4, 157.0) ;
	8	+
	9	+
	10	+#=======================================================================
	11	+
	12	+if nargin < 3,
	13	+ error ('Try make_filter (12, 32, 88, "output.txt")') ;
	14	+ endif
	15	+
	16	+if nargin < 4,
	17	+ filename = 0 ;
	18	+elseif (isstr (filename) == 0),
	19	+ error ("Fourth parameter must be a file name.") ;
	20	+ endif
	21	+
	22	+fudge_factor1 = 1.0 ;
	23	+f1 = generate_filter (cycles, fudge_factor1, increment, atten) ;
	24	+[stop_atten stop_band_start1 minus_3db] = measure_filter (f1, atten) ;
	25	+printf (" fudge_factor : %15.13f stop_band_start : %15.13f 1\n", fudge_factor1, stop_band_start1) ;
	26	+
	27	+fudge_factor2 = 1.25 ;
	28	+f2 = generate_filter (cycles, fudge_factor2, increment, atten) ;
	29	+[stop_atten stop_band_start2 minus_3db] = measure_filter (f2, atten) ;
	30	+printf (" fudge_factor : %15.13f stop_band_start : %15.13f 2\n", fudge_factor2, stop_band_start2) ;
	31	+
	32	+f = f1 ;
	33	+fudge_factor = fudge_factor1 ;
	34	+stop_band_start = stop_band_start1 ;
	35	+
	36	+while ((stop_band_start1 - stop_band_start2) > 0.0000000001)
	37	+ if (stop_band_start1 < stop_band_start2)
	38	+ printf ("stop_band_start1 < stop_band_start2\n") ;
	39	+ break ;
	40	+ endif
	41	+
	42	+ fudge_factor = fudge_factor1 + (fudge_factor2 - fudge_factor1) / 2 ;
	43	+ f = generate_filter (cycles, fudge_factor, increment, atten) ;
	44	+ [stop_atten stop_band_start minus_3db] = measure_filter (f, atten) ;
	45	+
	46	+ if (stop_band_start > 1.0)
	47	+ printf ("A %10.8f %10.8f %10.8f\n", fudge_factor1, fudge_factor, fudge_factor2) ;
	48	+ continue ;
	49	+ endif
	50	+
	51	+ if (stop_band_start < 0.5 / increment)
	52	+ f2 = f ;
	53	+ stop_band_start2 = stop_band_start ;
	54	+ fudge_factor2 = fudge_factor ;
	55	+ choice = 2 ;
	56	+ else
	57	+ f1 = f ;
	58	+ stop_band_start1 = stop_band_start ;
	59	+ fudge_factor1 = fudge_factor ;
	60	+ choice = 1 ;
	61	+ endif
	62	+
	63	+ printf (" fudge_factor : %15.13f stop_band_start : %15.13f %d\n", fudge_factor, stop_band_start, choice) ;
	64	+ endwhile
	65	+
	66	+printf ("\n") ;
	67	+
	68	+#-------------------------------------------------------------------------------
	69	+# Grab only half the coefficients.
	70	+
	71	+N = length (f) ;
	72	+
	73	+f = increment * f' ;
	74	+
	75	+if rem (length (f), 2) == 0,
	76	+ index = find (f == max (f)) ;
	77	+ index = min (index) - 1 ;
	78	+ half_f = f (index:length (f)) ;
	79	+else
	80	+ error ("Length should be even.") ;
	81	+ endif
	82	+
	83	+trailing_zeros = 4 - rem (length (half_f), 4) ;
	84	+
	85	+#-------------------------------------------------------------------------------
	86	+# Print analysis.
	87	+
	88	+printf ("# f = make_filter (%d, %d, %4.1f) ;\n", cycles, increment, atten) ;
	89	+printf ("# Coeff. count : %d\n", N) ;
	90	+printf ("# Fudge factor : %9.7f\n", fudge_factor) ;
	91	+printf ("# Pass band width : %12.10f (should be %12.10f)\n", stop_band_start, 0.5 / increment) ;
	92	+printf ("# Stop band atten. : %5.2f dB\n", abs (stop_atten)) ;
	93	+printf ("# -3dB band Width : %5.3f\n", 0.5 / increment / minus_3db) ;
	94	+printf ("# half length : %d\n", length (half_f) + trailing_zeros) ;
	95	+printf ("# increment : %d\n", increment) ;
	96	+
	97	+if filename,
	98	+ file = fopen (filename, "w") ;
	99	+ if file == 0,
	100	+ str = sprintf ("Error, not able to open '%s'", filename)
	101	+ error (str) ;
	102	+ endif
	103	+
	104	+ fprintf (file, "/*\n") ;
	105	+ fprintf (file, "** f = make_filter (%d, %d, %4.1f) ;\n", cycles, increment, atten) ;
	106	+ fprintf (file, "** Pass band width : %9.7f (should be %9.7f)\n", stop_band_start, 0.5 / increment) ;
	107	+ fprintf (file, "** Stop band atten. : %5.2f dB\n", abs (stop_atten)) ;
	108	+ fprintf (file, "** -3dB band width : %5.3f\n", 0.5 / increment / minus_3db) ;
	109	+ fprintf (file, "** half length : %d\n", length (half_f)) ;
	110	+ fprintf (file, "** increment : %d\n", increment) ;
	111	+ fprintf (file, "*/\n\n") ;
	112	+
	113	+ for val = half_f,
	114	+ fprintf (file, "% 24.20e,\n", val) ;
	115	+ endfor
	116	+
	117	+ if trailing_zeros > 0,
	118	+ for val = 2:trailing_zeros,
	119	+ fprintf (file, " 0,\n") ;
	120	+ endfor
	121	+ fprintf (file, " 0\n") ;
	122	+ endif
	123	+
	124	+ fclose (file) ;
	125	+ endif
	126	+
	127	+endfunction
	128	+
	129	+# Do not edit or modify anything in this comment block.
	130	+# The arch-tag line is a file identity tag for the GNU Arch
	131	+# revision control system.
	132	+#
	133	+# arch-tag: 2f1ff4fa-ea6a-4e54-a5f8-dad55def9834
	134	+

Octave/measure_filter.m+70−0

@@ -0,0 +1,70 @@
	1	+function [stop_atten stop_band_start minus_3db] = measure_filter (f, atten)
	2	+
	3	+
	4	+spec_len = 400000 ;
	5	+
	6	+# Calculate the spectrum.
	7	+
	8	+spec = 20 * log10 (abs (fft ([f zeros(1, spec_len - length (f))]))) ;
	9	+
	10	+spec = spec (1:spec_len/2) ;
	11	+
	12	+#-------------------------------------------------------------------------------
	13	+# Find the first null which starts off the stop band.
	14	+
	15	+first_null = 0 ;
	16	+for k = 2:length (spec) - 1,
	17	+ if spec (k) < -0.8 * atten && spec (k-1) > spec (k) && spec (k) < spec (k + 1),
	18	+ first_null = k ;
	19	+ break
	20	+ endif
	21	+ endfor
	22	+
	23	+#-------------------------------------------------------------------------------
	24	+# Find the stop band minimum attenuation.
	25	+
	26	+stop_atten = max (spec (first_null:length (spec))) ;
	27	+
	28	+#-------------------------------------------------------------------------------
	29	+# Find the x position on the transition band which has the same attenuation.
	30	+
	31	+atten_start = 0 ;
	32	+for k = 1:first_null,
	33	+ if spec (k) > stop_atten && spec (k + 1) < stop_atten,
	34	+ atten_start = k ;
	35	+ break ;
	36	+ endif
	37	+ endfor
	38	+
	39	+atten_start = atten_start - 1 ; # Arrays are 1 based so subtract 1.
	40	+
	41	+stop_band_start = atten_start + (stop_atten - spec (atten_start)) / (spec (atten_start+1) - spec (atten_start)) ;
	42	+
	43	+
	44	+stop_band_start = stop_band_start / spec_len ;
	45	+
	46	+#-------------------------------------------------------------------------------
	47	+# Find -3db point.
	48	+
	49	+minus_3db = 0 ;
	50	+for k = 1:first_null,
	51	+ if spec (k) > -3.0 && spec (k + 1) < -3.0,
	52	+ minus_3db = k ;
	53	+ break ;
	54	+ endif
	55	+ endfor
	56	+
	57	+minus_3db = minus_3db - 1 ; # Arrays are 1 based so subtract 1.
	58	+
	59	+minus_3db = minus_3db + (stop_atten - spec (minus_3db)) / (spec (minus_3db+1) - spec (minus_3db)) ;
	60	+
	61	+minus_3db = minus_3db / spec_len ;
	62	+
	63	+endfunction
	64	+
	65	+# Do not edit or modify anything in this comment block.
	66	+# The arch-tag line is a file identity tag for the GNU Arch
	67	+# revision control system.
	68	+#
	69	+# arch-tag: cc2bc9a2-d387-4fed-aa0a-570e91f17c99
	70	+

Add Octave scripts to generate filter coefficients

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