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5
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1 /*
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2 * SpanDSP - a series of DSP components for telephony
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3 *
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4 * noise.c - A low complexity audio noise generator, suitable for
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5 * real time generation (current AWGN, and Hoth)
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6 *
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7 * Written by Steve Underwood <steveu@coppice.org>
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8 *
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9 * Copyright (C) 2005 Steve Underwood
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10 *
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11 * All rights reserved.
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12 *
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13 * This program is free software; you can redistribute it and/or modify
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14 * it under the terms of the GNU General Public License version 2, as
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15 * published by the Free Software Foundation.
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16 *
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17 * This program is distributed in the hope that it will be useful,
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18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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20 * GNU General Public License for more details.
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21 *
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22 * You should have received a copy of the GNU General Public License
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23 * along with this program; if not, write to the Free Software
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24 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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25 *
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26 * $Id: noise.c,v 1.17 2006/11/28 16:59:56 steveu Exp $
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27 */
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28
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29 /*! \file */
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30
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31 #ifdef HAVE_CONFIG_H
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32 #include <config.h>
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33 #endif
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34
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35 #include <stdlib.h>
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36 #include <stdio.h>
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37 #include <inttypes.h>
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38 #include <memory.h>
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39 #if defined(HAVE_TGMATH_H)
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40 #include <tgmath.h>
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41 #endif
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42 #if defined(HAVE_MATH_H)
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43 #include <math.h>
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44 #endif
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45
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46 #include "spandsp/telephony.h"
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47 #include "spandsp/dc_restore.h"
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48 #include "spandsp/noise.h"
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49
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50 int16_t noise(noise_state_t *s)
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51 {
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52 int32_t val;
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53 int i;
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54
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55 /* The central limit theorem says if you add a few random numbers together,
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56 the result starts to look Gaussian. Quantities above 7 give diminishing
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57 returns. Quantites above 20 are exceedingly Gaussian. */
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58 val = 0;
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59 for (i = 0; i < s->quality; i++)
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60 {
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61 s->rndnum = 1664525U*s->rndnum + 1013904223U;
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62 val += ((int32_t) s->rndnum) >> 22;
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63 }
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64 if (s->class_of_noise == NOISE_CLASS_HOTH)
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65 {
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66 /* Hoth noise is room-like. It should be sculpted, at the high and low ends,
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67 and roll off at 5dB/octave across the main part of the band. However,
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68 merely rolling off at 6dB/octave across the band gets you close
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69 to the subjective effect. */
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70 s->state = (3*val + 5*s->state) >> 3;
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71 /* Bring the overall power level back to the pre-filtered level. This
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72 simple approx. leaves the signal about 0.35dB low. */
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73 val = s->state << 1;
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74 }
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75 return saturate((val*s->rms) >> 10);
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76 }
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77 /*- End of function --------------------------------------------------------*/
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78
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79 noise_state_t *noise_init_dbm0(noise_state_t *s, int seed, float level, int class_of_noise, int quality)
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80 {
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81 return noise_init_dbov(s, seed, (level - DBM0_MAX_POWER), class_of_noise, quality);
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82 }
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83 /*- End of function --------------------------------------------------------*/
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84
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85 noise_state_t *noise_init_dbov(noise_state_t *s, int seed, float level, int class_of_noise, int quality)
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86 {
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87 float rms;
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88
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89 memset(s, 0, sizeof(*s));
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90 s->rndnum = (uint32_t) seed;
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91 rms = 32768.0f*powf(10.0f, level/20.0f);
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92 if (quality < 4)
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93 s->quality = 4;
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94 else if (quality > 20)
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95 s->quality = 20;
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96 else
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97 s->quality = quality;
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98 if (class_of_noise == NOISE_CLASS_HOTH)
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99 {
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100 /* Allow for the gain of the filter */
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101 rms *= 1.043f;
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102 }
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103 s->rms = (int32_t) (rms*sqrt(12.0/quality));
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104 s->class_of_noise = class_of_noise;
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105 return s;
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106 }
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107 /*- End of function --------------------------------------------------------*/
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108 /*- End of file ------------------------------------------------------------*/
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