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(&det->notch, 39 (int32_t)(-0.7600000 * 32768.0), 40 (int32_t)(-0.1183852 * 32768.0), 41 (int32_t)(-0.5104039 * 32768.0), 42 (int32_t)(0.1567596 * 32768.0), 43 (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(&det->notch, 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