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1/* SPDX-License-Identifier: GPL-2.0-or-later */2/*3 * SpanDSP - a series of DSP components for telephony4 *5 * ec_disable_detector.h - A detector which should eventually meet the6 * G.164/G.165 requirements for detecting the7 * 2100Hz echo cancellor disable tone.8 *9 * Written by Steve Underwood <steveu@coppice.org>10 *11 * Copyright (C) 2001 Steve Underwood12 *13 * All rights reserved.14 */15 16#include "dsp_biquad.h"17 18struct 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 030#define TRUE (!FALSE)31 32static inline void33echo_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, due37 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 54static inline int55echo_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 in62 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 the66 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 * 877 && 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 } else86 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