/*
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* SpanDSP - a series of DSP components for telephony
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*
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* ec_disable_detector.h - A detector which should eventually meet the
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* G.164/G.165 requirements for detecting the
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* 2100Hz echo cancellor disable tone.
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*
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* Written by Steve Underwood <steveu@coppice.org>
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*
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* Copyright (C) 2001 Steve Underwood
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*
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* All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*/
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#include "dsp_biquad.h"
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struct ec_disable_detector_state {
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struct biquad2_state notch;
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int notch_level;
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int channel_level;
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int tone_present;
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int tone_cycle_duration;
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int good_cycles;
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int hit;
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};
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#define FALSE 0
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#define TRUE (!FALSE)
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static inline void
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echo_can_disable_detector_init(struct ec_disable_detector_state *det)
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{
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/* Elliptic notch */
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/* This is actually centred at 2095Hz, but gets the balance we want, due
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to the asymmetric walls of the notch */
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biquad2_init(&det->notch,
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(int32_t)(-0.7600000 * 32768.0),
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(int32_t)(-0.1183852 * 32768.0),
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(int32_t)(-0.5104039 * 32768.0),
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(int32_t)(0.1567596 * 32768.0),
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(int32_t)(1.0000000 * 32768.0));
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det->channel_level = 0;
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det->notch_level = 0;
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det->tone_present = FALSE;
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det->tone_cycle_duration = 0;
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det->good_cycles = 0;
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det->hit = 0;
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}
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/*- End of function --------------------------------------------------------*/
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static inline int
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echo_can_disable_detector_update(struct ec_disable_detector_state *det,
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int16_t amp)
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{
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int16_t notched;
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notched = biquad2(&det->notch, amp);
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/* Estimate the overall energy in the channel, and the energy in
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the notch (i.e. overall channel energy - tone energy => noise).
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Use abs instead of multiply for speed (is it really faster?).
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Damp the overall energy a little more for a stable result.
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Damp the notch energy a little less, so we don't damp out the
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blip every time the phase reverses */
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det->channel_level += ((abs(amp) - det->channel_level) >> 5);
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det->notch_level += ((abs(notched) - det->notch_level) >> 4);
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if (det->channel_level > 280) {
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/* There is adequate energy in the channel.
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Is it mostly at 2100Hz? */
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if (det->notch_level * 6 < det->channel_level) {
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/* The notch says yes, so we have the tone. */
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if (!det->tone_present) {
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/* Do we get a kick every 450+-25ms? */
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if (det->tone_cycle_duration >= 425 * 8
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&& det->tone_cycle_duration <= 475 * 8) {
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det->good_cycles++;
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if (det->good_cycles > 2)
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det->hit = TRUE;
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}
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det->tone_cycle_duration = 0;
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}
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det->tone_present = TRUE;
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} else
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det->tone_present = FALSE;
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det->tone_cycle_duration++;
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} else {
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det->tone_present = FALSE;
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det->tone_cycle_duration = 0;
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det->good_cycles = 0;
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}
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return det->hit;
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}
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/*- End of function --------------------------------------------------------*/
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/*- End of file ------------------------------------------------------------*/
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