/* SPDX-License-Identifier: GPL-2.0-or-later */ /* * SpanDSP - a series of DSP components for telephony * * ec_disable_detector.h - A detector which should eventually meet the * G.164/G.165 requirements for detecting the * 2100Hz echo cancellor disable tone. * * Written by Steve Underwood <steveu@coppice.org> * * Copyright (C) 2001 Steve Underwood * * All rights reserved. */ #include "dsp_biquad.h" struct ec_disable_detector_state { struct biquad2_state notch; int notch_level; int channel_level; int tone_present; int tone_cycle_duration; int good_cycles; int hit; }; #define FALSE 0 #define TRUE (!FALSE) static inline void echo_can_disable_detector_init(struct ec_disable_detector_state *det) { /* Elliptic notch */ /* This is actually centred at 2095Hz, but gets the balance we want, due to the asymmetric walls of the notch */ biquad2_init(&det->notch, (int32_t)(-0.7600000 * 32768.0), (int32_t)(-0.1183852 * 32768.0), (int32_t)(-0.5104039 * 32768.0), (int32_t)(0.1567596 * 32768.0), (int32_t)(1.0000000 * 32768.0)); det->channel_level = 0; det->notch_level = 0; det->tone_present = FALSE; det->tone_cycle_duration = 0; det->good_cycles = 0; det->hit = 0; } /*- End of function --------------------------------------------------------*/ static inline int echo_can_disable_detector_update(struct ec_disable_detector_state *det, int16_t amp) { int16_t notched; notched = biquad2(&det->notch, amp); /* Estimate the overall energy in the channel, and the energy in the notch (i.e. overall channel energy - tone energy => noise). Use abs instead of multiply for speed (is it really faster?). Damp the overall energy a little more for a stable result. Damp the notch energy a little less, so we don't damp out the blip every time the phase reverses */ det->channel_level += ((abs(amp) - det->channel_level) >> 5); det->notch_level += ((abs(notched) - det->notch_level) >> 4); if (det->channel_level > 280) { /* There is adequate energy in the channel. Is it mostly at 2100Hz? */ if (det->notch_level * 6 < det->channel_level) { /* The notch says yes, so we have the tone. */ if (!det->tone_present) { /* Do we get a kick every 450+-25ms? */ if (det->tone_cycle_duration >= 425 * 8 && det->tone_cycle_duration <= 475 * 8) { det->good_cycles++; if (det->good_cycles > 2) det->hit = TRUE; } det->tone_cycle_duration = 0; } det->tone_present = TRUE; } else det->tone_present = FALSE; det->tone_cycle_duration++; } else { det->tone_present = FALSE; det->tone_cycle_duration = 0; det->good_cycles = 0; } return det->hit; } /*- End of function --------------------------------------------------------*/ /*- End of file ------------------------------------------------------------*/