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 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 ------------------------------------------------------------*/ 111