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comparison spandsp-0.0.6pre17/src/spandsp/noise.h @ 4:26cd8f1ef0b1

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import spandsp-0.0.6pre17
author Peter Meerwald <pmeerw@cosy.sbg.ac.at>
date Fri, 25 Jun 2010 15:50:58 +0200
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3:c6c5a16ce2f2 4:26cd8f1ef0b1
1 /*
2 * SpanDSP - a series of DSP components for telephony
3 *
4 * noise.h - A low complexity audio noise generator, suitable for
5 * real time generation (current just approx AWGN)
6 *
7 * Written by Steve Underwood <steveu@coppice.org>
8 *
9 * Copyright (C) 2005 Steve Underwood
10 *
11 * All rights reserved.
12 *
13 * This program is free software; you can redistribute it and/or modify
14 * it under the terms of the GNU Lesser General Public License version 2.1,
15 * as published by the Free Software Foundation.
16 *
17 * This program is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Lesser General Public License for more details.
21 *
22 * You should have received a copy of the GNU Lesser General Public
23 * License along with this program; if not, write to the Free Software
24 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
25 *
26 * $Id: noise.h,v 1.17 2009/02/10 13:06:47 steveu Exp $
27 */
28
29 /*! \file */
30
31 #if !defined(_SPANDSP_NOISE_H_)
32 #define _SPANDSP_NOISE_H_
33
34 /*! \page noise_page Noise generation
35
36 \section noise_page_sec_1 What does it do?
37 It generates audio noise. Currently it only generates reasonable quality
38 AWGN. It is designed to be of sufficiently low complexity to generate large
39 volumes of reasonable quality noise, in real time.
40
41 Hoth noise is used to model indoor ambient noise when evaluating communications
42 systems such as telephones. It is named after D.F. Hoth, who made the first
43 systematic study of this. The official definition of Hoth noise is IEEE
44 standard 269-2001 (revised from 269-1992), "Draft Standard Methods for Measuring
45 Transmission Performance of Analog and Digital Telephone Sets, Handsets and Headsets."
46
47 The table below gives the spectral density of Hoth noise, adjusted in level to produce
48 a reading of 50 dBA.
49
50 Freq (Hz) Spectral Bandwidth Total power in
51 density 10 log_f each 1/3 octave band
52 (dB SPL/Hz) (dB) (dB SPL)
53 100 32.4 13.5 45.9
54 125 30.9 14.7 45.5
55 160 29.1 15.7 44.9
56 200 27.6 16.5 44.1
57 250 26.0 17.6 43.6
58 315 24.4 18.7 43.1
59 400 22.7 19.7 42.3
60 500 21.1 20.6 41.7
61 630 19.5 21.7 41.2
62 800 17.8 22.7 40.4
63 1000 16.2 23.5 39.7
64 1250 14.6 24.7 39.3
65 1600 12.9 25.7 38.7
66 2000 11.3 26.5 37.8
67 2500 9.6 27.6 37.2
68 3150 7.8 28.7 36.5
69 4000 5.4 29.7 34.8
70 5000 2.6 30.6 33.2
71 6300 -1.3 31.7 30.4
72 8000 -6.6 32.7 26.0
73
74 The tolerance for each 1/3rd octave band is กำ3dB.
75
76 \section awgn_page_sec_2 How does it work?
77 The central limit theorem says if you add a few random numbers together,
78 the result starts to look Gaussian. In this case we sum 8 random numbers.
79 The result is fast, and perfectly good as a noise source for many purposes.
80 It should not be trusted as a high quality AWGN generator, for elaborate
81 modelling purposes.
82 */
83
84 enum
85 {
86 NOISE_CLASS_AWGN = 1,
87 NOISE_CLASS_HOTH
88 };
89
90 /*!
91 Noise generator descriptor. This contains all the state information for an instance
92 of the noise generator.
93 */
94 typedef struct noise_state_s noise_state_t;
95
96 #if defined(__cplusplus)
97 extern "C"
98 {
99 #endif
100
101 /*! Initialise an audio noise generator.
102 \brief Initialise an audio noise generator.
103 \param s The noise generator context.
104 \param seed A seed for the underlying random number generator.
105 \param level The noise power level in dBmO.
106 \param class_of_noise The class of noise (e.g. AWGN).
107 \param quality A parameter which permits speed and accuracy of the noise
108 generation to be adjusted.
109 \return A pointer to the noise generator context.
110 */
111 SPAN_DECLARE(noise_state_t *) noise_init_dbm0(noise_state_t *s, int seed, float level, int class_of_noise, int quality);
112
113 SPAN_DECLARE(noise_state_t *) noise_init_dbov(noise_state_t *s, int seed, float level, int class_of_noise, int quality);
114
115 SPAN_DECLARE(int) noise_release(noise_state_t *s);
116
117 SPAN_DECLARE(int) noise_free(noise_state_t *s);
118
119 /*! Generate a sample of audio noise.
120 \brief Generate a sample of audio noise.
121 \param s The noise generator context.
122 \return The generated sample.
123 */
124 SPAN_DECLARE(int16_t) noise(noise_state_t *s);
125
126 #if defined(__cplusplus)
127 }
128 #endif
129
130 #endif
131 /*- End of file ------------------------------------------------------------*/

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