LXR linux/drivers/isdn/mISDN/dsp

   1/* SPDX-License-Identifier: GPL-2.0-or-later */
   2/*
   3 * SpanDSP - a series of DSP components for telephony
   4 *
   5 * ec_disable_detector.h - A detector which should eventually meet the
   6 *                         G.164/G.165 requirements for detecting the
   7 *                         2100Hz echo cancellor disable tone.
   8 *
   9 * Written by Steve Underwood <steveu@coppice.org>
  10 *
  11 * Copyright (C) 2001 Steve Underwood
  12 *
  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 0
  30#define TRUE (!FALSE)
  31
  32static inline void
  33echo_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, due
  37           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 int
  55echo_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 in
  62           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 the
  66           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 * 8
  77                                    && 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                } else
  86                        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