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| Rev | Author | Line No. | Line |
|---|---|---|---|
| 3960 | Serge | 1 | /* |
| 2 | dither: Generate shaped noise for dithering |
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| 3 | |||
| 4 | copyright 2009 by the mpg123 project - free software under the terms of the LGPL 2.1 |
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| 5 | see COPYING and AUTHORS files in distribution or http://mpg123.org |
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| 6 | initially written by Taihei Monma |
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| 7 | */ |
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| 8 | |||
| 9 | #include "config.h" |
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| 10 | #include "compat.h" |
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| 11 | #include "dither.h" |
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| 12 | |||
| 13 | static const uint32_t init_seed = 2463534242UL; |
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| 14 | |||
| 15 | #define LAP 100 |
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| 16 | |||
| 17 | /* |
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| 18 | xorshift random number generator, with output scaling to [-0.5, 0.5] |
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| 19 | This is the white noise... |
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| 20 | See http://www.jstatsoft.org/v08/i14/paper on XOR shift random number generators. |
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| 21 | */ |
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| 22 | static float rand_xorshift32(uint32_t *seed) |
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| 23 | { |
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| 24 | union |
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| 25 | { |
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| 26 | uint32_t i; |
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| 27 | float f; |
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| 28 | } fi; |
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| 29 | |||
| 30 | fi.i = *seed; |
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| 31 | fi.i ^= (fi.i<<13); |
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| 32 | fi.i ^= (fi.i>>17); |
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| 33 | fi.i ^= (fi.i<<5); |
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| 34 | *seed = fi.i; |
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| 35 | |||
| 36 | /* scale the number to [-0.5, 0.5] */ |
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| 37 | #ifdef IEEE_FLOAT |
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| 38 | fi.i = (fi.i>>9)|0x3f800000; |
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| 39 | fi.f -= 1.5f; |
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| 40 | #else |
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| 41 | fi.f = (double)fi.i / 4294967295.0; |
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| 42 | fi.f -= 0.5f; |
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| 43 | #endif |
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| 44 | return fi.f; |
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| 45 | } |
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| 46 | |||
| 47 | static void white_noise(float *table, size_t count) |
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| 48 | { |
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| 49 | size_t i; |
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| 50 | uint32_t seed = init_seed; |
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| 51 | |||
| 52 | for(i=0; i |
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| 53 | table[i] = rand_xorshift32(&seed); |
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| 54 | } |
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| 55 | |||
| 56 | static void tpdf_noise(float *table, size_t count) |
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| 57 | { |
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| 58 | size_t i; |
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| 59 | uint32_t seed = init_seed; |
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| 60 | |||
| 61 | for(i=0; i |
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| 62 | table[i] = rand_xorshift32(&seed) + rand_xorshift32(&seed); |
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| 63 | } |
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| 64 | |||
| 65 | static void highpass_tpdf_noise(float *table, size_t count) |
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| 66 | { |
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| 67 | size_t i; |
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| 68 | uint32_t seed = init_seed; |
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| 69 | /* Ensure some minimum lap for keeping the high-pass filter circular. */ |
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| 70 | size_t lap = count > 2*LAP ? LAP : count/2; |
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| 71 | |||
| 72 | float input_noise; |
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| 73 | float xv[9], yv[9]; |
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| 74 | |||
| 75 | for(i=0;i<9;i++) |
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| 76 | { |
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| 77 | xv[i] = yv[i] = 0.0f; |
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| 78 | } |
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| 79 | |||
| 80 | for(i=0;i |
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| 81 | { |
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| 82 | if(i==count) seed=init_seed; |
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| 83 | |||
| 84 | /* generate and add 2 random numbers, to make a TPDF noise distribution */ |
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| 85 | input_noise = rand_xorshift32(&seed) + rand_xorshift32(&seed); |
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| 86 | |||
| 87 | /* apply 8th order Chebyshev high-pass IIR filter */ |
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| 88 | /* Coefficients are from http://www-users.cs.york.ac.uk/~fisher/mkfilter/trad.html |
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| 89 | Given parameters are: Chebyshev, Highpass, ripple=-1, order=8, samplerate=44100, corner1=19000 */ |
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| 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]; |
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| 91 | xv[8] = input_noise / 1.382814179e+07; |
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| 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]; |
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| 93 | yv[8] = (xv[0] + xv[8]) - 8 * (xv[1] + xv[7]) + 28 * (xv[2] + xv[6]) |
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| 94 | - 56 * (xv[3] + xv[5]) + 70 * xv[4] |
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| 95 | + ( -0.6706204984 * yv[0]) + ( -5.3720827038 * yv[1]) |
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| 96 | + (-19.0865382480 * yv[2]) + (-39.2831607860 * yv[3]) |
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| 97 | + (-51.2308985070 * yv[4]) + (-43.3590135780 * yv[5]) |
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| 98 | + (-23.2632305320 * yv[6]) + ( -7.2370122050 * yv[7]); |
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| 99 | if(i>=lap) table[i-lap] = yv[8] * 3.0f; |
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| 100 | } |
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| 101 | } |
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| 102 | |||
| 103 | void mpg123_noise(float* table, size_t count, enum mpg123_noise_type noisetype) |
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| 104 | { |
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| 105 | switch(noisetype) |
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| 106 | { |
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| 107 | case mpg123_white_noise: white_noise(table, count); break; |
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| 108 | case mpg123_tpdf_noise: tpdf_noise(table, count); break; |
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| 109 | case mpg123_highpass_tpdf_noise: |
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| 110 | highpass_tpdf_noise(table, count); |
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| 111 | break; |
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| 112 | } |
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| 113 | } |
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| 114 | |||
| 115 | /* Generate white noise and shape it with a high pass filter. */ |
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| 116 | void dither_table_init(float *dithertable) |
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| 117 | { |
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| 118 | highpass_tpdf_noise(dithertable, DITHERSIZE); |
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| 119 | } |