drivers/isdn/mISDN/dsp_ecdis.h

   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 ------------------------------------------------------------*/