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comparison spandsp-0.0.3/spandsp-0.0.3/src/spandsp/modem_connect_tones.h @ 5:f762bf195c4b

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import spandsp-0.0.3
author Peter Meerwald <pmeerw@cosy.sbg.ac.at>
date Fri, 25 Jun 2010 16:00:21 +0200
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4:26cd8f1ef0b1 5:f762bf195c4b
1 /*
2 * SpanDSP - a series of DSP components for telephony
3 *
4 * modem_connect_tones.c - Generation and detection of tones
5 * associated with modems calling and answering calls.
6 *
7 * Written by Steve Underwood <steveu@coppice.org>
8 *
9 * Copyright (C) 2006 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 General Public License version 2, as
15 * 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 General Public License for more details.
21 *
22 * You should have received a copy of the GNU General Public License
23 * along with this program; if not, write to the Free Software
24 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
25 *
26 * $Id: modem_connect_tones.h,v 1.4 2006/10/24 13:45:28 steveu Exp $
27 */
28
29 /*! \file */
30
31 #if !defined(_MODEM_CONNECT_TONES_H_)
32 #define _MODEM_CONNECT_TONES_H_
33
34 /*! \page modem_connect_tones_page Echo cancellor disable tone detection
35
36 \section modem_connect_tones_page_sec_1 What does it do?
37 Some telephony terminal equipment, such as modems, require a channel which is as
38 clear as possible. They use their own echo cancellation. If the network is also
39 performing echo cancellation the two cancellors can end of squabbling about the
40 nature of the channel, with bad results. A special tone is defined which should
41 cause the network to disable any echo cancellation processes.
42
43 \section modem_connect_tones_page_sec_2 How does it work?
44 A sharp notch filter is implemented as a single bi-quad section. The presence of
45 the 2100Hz disable tone is detected by comparing the notched filtered energy
46 with the unfiltered energy. If the notch filtered energy is much lower than the
47 unfiltered energy, then a large proportion of the energy must be at the notch
48 frequency. This type of detector may seem less intuitive than using a narrow
49 bandpass filter to isolate the energy at the notch freqency. However, a sharp
50 bandpass implemented as an IIR filter rings badly, The reciprocal notch filter
51 is very well behaved.
52 */
53
54 enum
55 {
56 MODEM_CONNECT_TONES_FAX_CNG,
57 MODEM_CONNECT_TONES_FAX_CED,
58 MODEM_CONNECT_TONES_EC_DISABLE,
59 /*! \brief The version of EC disable with some 15Hz AM content, as in V.8 */
60 MODEM_CONNECT_TONES_EC_DISABLE_MOD,
61 };
62
63 /*!
64 Modem connect tones generator descriptor. This defines the state
65 of a single working instance of the tone generator.
66 */
67 typedef struct
68 {
69 int tone_type;
70
71 tone_gen_state_t tone_tx;
72 uint32_t tone_phase;
73 int32_t tone_phase_rate;
74 int level;
75 /*! \brief Countdown to the next phase hop */
76 int hop_timer;
77 uint32_t mod_phase;
78 int32_t mod_phase_rate;
79 int mod_level;
80 } modem_connect_tones_tx_state_t;
81
82 /*!
83 Modem connect tones receiver descriptor. This defines the state
84 of a single working instance of the tone detector.
85 */
86 typedef struct
87 {
88 int tone_type;
89 tone_report_func_t tone_callback;
90 void *callback_data;
91
92 float z1;
93 float z2;
94 int notch_level;
95 int channel_level;
96 int tone_present;
97 int tone_cycle_duration;
98 int good_cycles;
99 int hit;
100 } modem_connect_tones_rx_state_t;
101
102 #ifdef __cplusplus
103 extern "C" {
104 #endif
105
106 /*! \brief Initialse an instance of the echo canceller disable tone generator.
107 \param s The context.
108 */
109 modem_connect_tones_tx_state_t *modem_connect_tones_tx_init(modem_connect_tones_tx_state_t *s,
110 int tone_type);
111
112 /*! \brief Generate a block of echo canceller disable tone samples.
113 \param s The context.
114 \param amp An array of signal samples.
115 \param len The number of samples to generate.
116 \return The number of samples generated.
117 */
118 int modem_connect_tones_tx(modem_connect_tones_tx_state_t *s,
119 int16_t amp[],
120 int len);
121
122 /*! \brief Process a block of samples through an instance of the modem_connect
123 tones detector.
124 \param s The context.
125 \param amp An array of signal samples.
126 \param len The number of samples in the array.
127 \return The number of unprocessed samples.
128 */
129 int modem_connect_tones_rx(modem_connect_tones_rx_state_t *s,
130 const int16_t amp[],
131 int len);
132
133 /*! \brief Test if a modem_connect tone has been detected.
134 \param s The context.
135 \return TRUE if tone is detected, else FALSE.
136 */
137 int modem_connect_tones_rx_get(modem_connect_tones_rx_state_t *s);
138
139 /*! \brief Initialise an instance of the modem_connect tones detector.
140 \param s The context.
141 \param tone_type The type of connect tone being tested for.
142 \param tone_callback An optional callback routine, used to report tones
143 \param user_data An opaque pointer passed to the callback routine,
144 \return A pointer to the context.
145 */
146 modem_connect_tones_rx_state_t *modem_connect_tones_rx_init(modem_connect_tones_rx_state_t *s,
147 int tone_type,
148 tone_report_func_t tone_callback,
149 void *user_data);
150
151 #ifdef __cplusplus
152 }
153 #endif
154
155 #endif
156 /*- End of file ------------------------------------------------------------*/

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