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dsp_ecdis.h
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1 /*
2  * SpanDSP - a series of DSP components for telephony
3  *
4  * ec_disable_detector.h - A detector which should eventually meet the
5  * G.164/G.165 requirements for detecting the
6  * 2100Hz echo cancellor disable tone.
7  *
8  * Written by Steve Underwood <[email protected]>
9  *
10  * Copyright (C) 2001 Steve Underwood
11  *
12  * All rights reserved.
13  *
14  * This program is free software; you can redistribute it and/or modify
15  * it under the terms of the GNU General Public License as published by
16  * the Free Software Foundation; either version 2 of the License, or
17  * (at your option) any later version.
18  *
19  * This program is distributed in the hope that it will be useful,
20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22  * GNU General Public License for more details.
23  *
24  * You should have received a copy of the GNU General Public License
25  * along with this program; if not, write to the Free Software
26  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
27  *
28  */
29 
30 #include "dsp_biquad.h"
31 
32 struct ec_disable_detector_state {
33  struct biquad2_state notch;
34  int notch_level;
35  int channel_level;
36  int tone_present;
37  int tone_cycle_duration;
38  int good_cycles;
39  int hit;
40 };
41 
42 
43 #define FALSE 0
44 #define TRUE (!FALSE)
45 
46 static inline void
47 echo_can_disable_detector_init(struct ec_disable_detector_state *det)
48 {
49  /* Elliptic notch */
50  /* This is actually centred at 2095Hz, but gets the balance we want, due
51  to the asymmetric walls of the notch */
52  biquad2_init(&det->notch,
53  (int32_t)(-0.7600000 * 32768.0),
54  (int32_t)(-0.1183852 * 32768.0),
55  (int32_t)(-0.5104039 * 32768.0),
56  (int32_t)(0.1567596 * 32768.0),
57  (int32_t)(1.0000000 * 32768.0));
58 
59  det->channel_level = 0;
60  det->notch_level = 0;
61  det->tone_present = FALSE;
62  det->tone_cycle_duration = 0;
63  det->good_cycles = 0;
64  det->hit = 0;
65 }
66 /*- End of function --------------------------------------------------------*/
67 
68 static inline int
69 echo_can_disable_detector_update(struct ec_disable_detector_state *det,
70  int16_t amp)
71 {
72  int16_t notched;
73 
74  notched = biquad2(&det->notch, amp);
75  /* Estimate the overall energy in the channel, and the energy in
76  the notch (i.e. overall channel energy - tone energy => noise).
77  Use abs instead of multiply for speed (is it really faster?).
78  Damp the overall energy a little more for a stable result.
79  Damp the notch energy a little less, so we don't damp out the
80  blip every time the phase reverses */
81  det->channel_level += ((abs(amp) - det->channel_level) >> 5);
82  det->notch_level += ((abs(notched) - det->notch_level) >> 4);
83  if (det->channel_level > 280) {
84  /* There is adequate energy in the channel.
85  Is it mostly at 2100Hz? */
86  if (det->notch_level * 6 < det->channel_level) {
87  /* The notch says yes, so we have the tone. */
88  if (!det->tone_present) {
89  /* Do we get a kick every 450+-25ms? */
90  if (det->tone_cycle_duration >= 425 * 8
91  && det->tone_cycle_duration <= 475 * 8) {
92  det->good_cycles++;
93  if (det->good_cycles > 2)
94  det->hit = TRUE;
95  }
96  det->tone_cycle_duration = 0;
97  }
98  det->tone_present = TRUE;
99  } else
100  det->tone_present = FALSE;
101  det->tone_cycle_duration++;
102  } else {
103  det->tone_present = FALSE;
104  det->tone_cycle_duration = 0;
105  det->good_cycles = 0;
106  }
107  return det->hit;
108 }
109 /*- End of function --------------------------------------------------------*/
110 /*- End of file ------------------------------------------------------------*/
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