1 /*
2 dither: Generate shaped noise for dithering
3
4 copyright 2009 by the mpg123 project - free software under the terms of the LGPL 2.1
5 see COPYING and AUTHORS files in distribution or http://mpg123.org
6 initially written by Taihei Monma
7 */
8
9 #include "config.h"
10 #include "compat.h"
11 #include "dither.h"
12
13 static const uint32_t init_seed = 2463534242UL;
14
15 #define LAP 100
16
17 /*
18 xorshift random number generator, with output scaling to [-0.5, 0.5]
19 This is the white noise...
20 See http://www.jstatsoft.org/v08/i14/paper on XOR shift random number generators.
21 */
rand_xorshift32(uint32_t * seed)22 static float rand_xorshift32(uint32_t *seed)
23 {
24 union
25 {
26 uint32_t i;
27 float f;
28 } fi;
29
30 fi.i = *seed;
31 fi.i ^= (fi.i<<13);
32 fi.i ^= (fi.i>>17);
33 fi.i ^= (fi.i<<5);
34 *seed = fi.i;
35
36 /* scale the number to [-0.5, 0.5] */
37 #ifdef IEEE_FLOAT
38 fi.i = (fi.i>>9)|0x3f800000;
39 fi.f -= 1.5f;
40 #else
41 fi.f = (double)fi.i / 4294967295.0;
42 fi.f -= 0.5f;
43 #endif
44 return fi.f;
45 }
46
white_noise(float * table,size_t count)47 static void white_noise(float *table, size_t count)
48 {
49 size_t i;
50 uint32_t seed = init_seed;
51
52 for(i=0; i<count; ++i)
53 table[i] = rand_xorshift32(&seed);
54 }
55
tpdf_noise(float * table,size_t count)56 static void tpdf_noise(float *table, size_t count)
57 {
58 size_t i;
59 uint32_t seed = init_seed;
60
61 for(i=0; i<count; ++i)
62 table[i] = rand_xorshift32(&seed) + rand_xorshift32(&seed);
63 }
64
highpass_tpdf_noise(float * table,size_t count)65 static void highpass_tpdf_noise(float *table, size_t count)
66 {
67 size_t i;
68 uint32_t seed = init_seed;
69 /* Ensure some minimum lap for keeping the high-pass filter circular. */
70 size_t lap = count > 2*LAP ? LAP : count/2;
71
72 float input_noise;
73 float xv[9], yv[9];
74
75 for(i=0;i<9;i++)
76 {
77 xv[i] = yv[i] = 0.0f;
78 }
79
80 for(i=0;i<count+lap;i++)
81 {
82 if(i==count) seed=init_seed;
83
84 /* generate and add 2 random numbers, to make a TPDF noise distribution */
85 input_noise = rand_xorshift32(&seed) + rand_xorshift32(&seed);
86
87 /* apply 8th order Chebyshev high-pass IIR filter */
88 /* Coefficients are from http://www-users.cs.york.ac.uk/~fisher/mkfilter/trad.html
89 Given parameters are: Chebyshev, Highpass, ripple=-1, order=8, samplerate=44100, corner1=19000 */
90 xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3]; xv[3] = xv[4]; xv[4] = xv[5]; xv[5] = xv[6]; xv[6] = xv[7]; xv[7] = xv[8];
91 xv[8] = input_noise / 1.382814179e+07;
92 yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3]; yv[3] = yv[4]; yv[4] = yv[5]; yv[5] = yv[6]; yv[6] = yv[7]; yv[7] = yv[8];
93 yv[8] = (xv[0] + xv[8]) - 8 * (xv[1] + xv[7]) + 28 * (xv[2] + xv[6])
94 - 56 * (xv[3] + xv[5]) + 70 * xv[4]
95 + ( -0.6706204984 * yv[0]) + ( -5.3720827038 * yv[1])
96 + (-19.0865382480 * yv[2]) + (-39.2831607860 * yv[3])
97 + (-51.2308985070 * yv[4]) + (-43.3590135780 * yv[5])
98 + (-23.2632305320 * yv[6]) + ( -7.2370122050 * yv[7]);
99 if(i>=lap) table[i-lap] = yv[8] * 3.0f;
100 }
101 }
102
mpg123_noise(float * table,size_t count,enum mpg123_noise_type noisetype)103 void mpg123_noise(float* table, size_t count, enum mpg123_noise_type noisetype)
104 {
105 switch(noisetype)
106 {
107 case mpg123_white_noise: white_noise(table, count); break;
108 case mpg123_tpdf_noise: tpdf_noise(table, count); break;
109 case mpg123_highpass_tpdf_noise:
110 highpass_tpdf_noise(table, count);
111 break;
112 }
113 }
114
115 /* Generate white noise and shape it with a high pass filter. */
dither_table_init(float * dithertable)116 void dither_table_init(float *dithertable)
117 {
118 highpass_tpdf_noise(dithertable, DITHERSIZE);
119 }
120