diff options
Diffstat (limited to 'drivers/isdn/mISDN/dsp_ecdis.h')
| -rw-r--r-- | drivers/isdn/mISDN/dsp_ecdis.h | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/drivers/isdn/mISDN/dsp_ecdis.h b/drivers/isdn/mISDN/dsp_ecdis.h new file mode 100644 index 00000000..21dbd153 --- /dev/null +++ b/drivers/isdn/mISDN/dsp_ecdis.h @@ -0,0 +1,110 @@ +/* + * 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 "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 ------------------------------------------------------------*/ |