1 | /* SPDX-License-Identifier: GPL-2.0-or-later */ |
2 | /* |
3 | * SpanDSP - a series of DSP components for telephony |
4 | * |
5 | * ec_disable_detector.h - A detector which should eventually meet the |
6 | * G.164/G.165 requirements for detecting the |
7 | * 2100Hz echo cancellor disable tone. |
8 | * |
9 | * Written by Steve Underwood <steveu@coppice.org> |
10 | * |
11 | * Copyright (C) 2001 Steve Underwood |
12 | * |
13 | * All rights reserved. |
14 | */ |
15 | |
16 | #include "dsp_biquad.h" |
17 | |
18 | struct ec_disable_detector_state { |
19 | struct biquad2_state notch; |
20 | int notch_level; |
21 | int channel_level; |
22 | int tone_present; |
23 | int tone_cycle_duration; |
24 | int good_cycles; |
25 | int hit; |
26 | }; |
27 | |
28 | |
29 | #define FALSE 0 |
30 | #define TRUE (!FALSE) |
31 | |
32 | static inline void |
33 | echo_can_disable_detector_init(struct ec_disable_detector_state *det) |
34 | { |
35 | /* Elliptic notch */ |
36 | /* This is actually centred at 2095Hz, but gets the balance we want, due |
37 | to the asymmetric walls of the notch */ |
38 | biquad2_init(bq: &det->notch, |
39 | gain: (int32_t)(-0.7600000 * 32768.0), |
40 | a1: (int32_t)(-0.1183852 * 32768.0), |
41 | a2: (int32_t)(-0.5104039 * 32768.0), |
42 | b1: (int32_t)(0.1567596 * 32768.0), |
43 | b2: (int32_t)(1.0000000 * 32768.0)); |
44 | |
45 | det->channel_level = 0; |
46 | det->notch_level = 0; |
47 | det->tone_present = FALSE; |
48 | det->tone_cycle_duration = 0; |
49 | det->good_cycles = 0; |
50 | det->hit = 0; |
51 | } |
52 | /*- End of function --------------------------------------------------------*/ |
53 | |
54 | static inline int |
55 | echo_can_disable_detector_update(struct ec_disable_detector_state *det, |
56 | int16_t amp) |
57 | { |
58 | int16_t notched; |
59 | |
60 | notched = biquad2(bq: &det->notch, sample: amp); |
61 | /* Estimate the overall energy in the channel, and the energy in |
62 | the notch (i.e. overall channel energy - tone energy => noise). |
63 | Use abs instead of multiply for speed (is it really faster?). |
64 | Damp the overall energy a little more for a stable result. |
65 | Damp the notch energy a little less, so we don't damp out the |
66 | blip every time the phase reverses */ |
67 | det->channel_level += ((abs(amp) - det->channel_level) >> 5); |
68 | det->notch_level += ((abs(notched) - det->notch_level) >> 4); |
69 | if (det->channel_level > 280) { |
70 | /* There is adequate energy in the channel. |
71 | Is it mostly at 2100Hz? */ |
72 | if (det->notch_level * 6 < det->channel_level) { |
73 | /* The notch says yes, so we have the tone. */ |
74 | if (!det->tone_present) { |
75 | /* Do we get a kick every 450+-25ms? */ |
76 | if (det->tone_cycle_duration >= 425 * 8 |
77 | && det->tone_cycle_duration <= 475 * 8) { |
78 | det->good_cycles++; |
79 | if (det->good_cycles > 2) |
80 | det->hit = TRUE; |
81 | } |
82 | det->tone_cycle_duration = 0; |
83 | } |
84 | det->tone_present = TRUE; |
85 | } else |
86 | det->tone_present = FALSE; |
87 | det->tone_cycle_duration++; |
88 | } else { |
89 | det->tone_present = FALSE; |
90 | det->tone_cycle_duration = 0; |
91 | det->good_cycles = 0; |
92 | } |
93 | return det->hit; |
94 | } |
95 | /*- End of function --------------------------------------------------------*/ |
96 | /*- End of file ------------------------------------------------------------*/ |
97 | |