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 <steveu@coppice.org>
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
echo_can_disable_detector_init(struct ec_disable_detector_state * det)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
echo_can_disable_detector_update(struct ec_disable_detector_state * det,int16_t amp)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 ------------------------------------------------------------*/
111