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/*
* 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.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
*/
#include "biquad.h"
typedef struct
{
biquad2_state_t notch;
int notch_level;
int channel_level;
int tone_present;
int tone_cycle_duration;
int good_cycles;
int hit;
} echo_can_disable_detector_state_t;
#define FALSE 0
#define TRUE (!FALSE)
static inline void echo_can_disable_detector_init (echo_can_disable_detector_state_t *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 (echo_can_disable_detector_state_t *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 ------------------------------------------------------------*/
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