Mercurial > hg > audiostuff

comparison spandsp-0.0.3/spandsp-0.0.3/src/modem_echo.c @ 5:f762bf195c4b

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
import spandsp-0.0.3
author Peter Meerwald <pmeerw@cosy.sbg.ac.at>
date Fri, 25 Jun 2010 16:00:21 +0200
parents
children
comparison
equal deleted inserted replaced
4:26cd8f1ef0b1 5:f762bf195c4b
1 /*
2 * SpanDSP - a series of DSP components for telephony
3 *
4 * modem_echo.c - An echo cancellor, suitable for electrical echos in GSTN modems
5 *
6 * Written by Steve Underwood <steveu@coppice.org>
7 *
8 * Copyright (C) 2001, 2003, 2004 Steve Underwood
9 *
10 * All rights reserved.
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License version 2, as
14 * published by the Free Software Foundation.
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
20 *
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24 *
25 * $Id: modem_echo.c,v 1.17 2006/11/19 14:07:24 steveu Exp $
26 */
27
28 /*! \file */
29
30 /* The FIR taps must be adapted as 32 bit values, to get the necessary finesse
31 in the adaption process. However, they are applied as 16 bit values (bits 30-15
32 of the 32 bit values) in the FIR. For the working 16 bit values, we need 4 sets.
33 */
34
35 #ifdef HAVE_CONFIG_H
36 #include <config.h>
37 #endif
38
39 #include <stdlib.h>
40 #include <inttypes.h>
41 #include <string.h>
42 #include <stdio.h>
43 #if defined(HAVE_TGMATH_H)
44 #include <tgmath.h>
45 #endif
46 #if defined(HAVE_MATH_H)
47 #include <math.h>
48 #endif
49
50 #include "spandsp/telephony.h"
51 #include "spandsp/bit_operations.h"
52 #include "spandsp/dc_restore.h"
53 #include "spandsp/modem_echo.h"
54
55 modem_echo_can_state_t *modem_echo_can_create(int len)
56 {
57 modem_echo_can_state_t *ec;
58
59 ec = (modem_echo_can_state_t *) malloc(sizeof(*ec));
60 if (ec == NULL)
61 return NULL;
62 memset(ec, 0, sizeof(*ec));
63 ec->taps = len;
64 ec->curr_pos = ec->taps - 1;
65 if ((ec->fir_taps32 = (int32_t *) malloc(ec->taps*sizeof(int32_t))) == NULL)
66 {
67 free(ec);
68 return NULL;
69 }
70 memset(ec->fir_taps32, 0, ec->taps*sizeof(int32_t));
71 if ((ec->fir_taps16 = (int16_t *) malloc(ec->taps*sizeof(int16_t))) == NULL)
72 {
73 free(ec->fir_taps32);
74 free(ec);
75 return NULL;
76 }
77 memset(ec->fir_taps16, 0, ec->taps*sizeof(int16_t));
78 if (fir16_create(&ec->fir_state, ec->fir_taps16, ec->taps) == NULL)
79 {
80 free(ec->fir_taps16);
81 free(ec->fir_taps32);
82 free(ec);
83 return NULL;
84 }
85 return ec;
86 }
87 /*- End of function --------------------------------------------------------*/
88
89 void modem_echo_can_free(modem_echo_can_state_t *ec)
90 {
91 fir16_free(&ec->fir_state);
92 free(ec->fir_taps32);
93 free(ec->fir_taps16);
94 free(ec);
95 }
96 /*- End of function --------------------------------------------------------*/
97
98 void modem_echo_can_flush(modem_echo_can_state_t *ec)
99 {
100 ec->tx_power = 0;
101
102 fir16_flush(&ec->fir_state);
103 ec->fir_state.curr_pos = ec->taps - 1;
104 memset(ec->fir_taps32, 0, ec->taps*sizeof(int32_t));
105 memset(ec->fir_taps16, 0, ec->taps*sizeof(int16_t));
106 ec->curr_pos = ec->taps - 1;
107 }
108 /*- End of function --------------------------------------------------------*/
109
110 void modem_echo_can_adaption_mode(modem_echo_can_state_t *ec, int adapt)
111 {
112 ec->adapt = adapt;
113 }
114 /*- End of function --------------------------------------------------------*/
115
116 int16_t modem_echo_can_update(modem_echo_can_state_t *ec, int16_t tx, int16_t rx)
117 {
118 int32_t echo_value;
119 int clean_rx;
120 int shift;
121 int i;
122 int offset1;
123 int offset2;
124
125 /* Evaluate the echo - i.e. apply the FIR filter */
126 /* Assume the gain of the FIR does not exceed unity. Exceeding unity
127 would seem like a rather poor thing for an echo cancellor to do :)
128 This means we can compute the result with a total disregard for
129 overflows. 16bits x 16bits -> 31bits, so no overflow can occur in
130 any multiply. While accumulating we may overflow and underflow the
131 32 bit scale often. However, if the gain does not exceed unity,
132 everything should work itself out, and the final result will be
133 OK, without any saturation logic. */
134 /* Overflow is very much possible here, and we do nothing about it because
135 of the compute costs */
136 echo_value = fir16(&ec->fir_state, tx);
137
138 /* And the answer is..... */
139 clean_rx = rx - echo_value;
140 //printf("%8d %8d %8d %8d\n", tx, rx, echo_value, clean_rx);
141 if (ec->adapt)
142 {
143 /* Calculate short term power levels using very simple single pole IIRs */
144 /* TODO: Is the nasty modulus approach the fastest, or would a real
145 tx*tx power calculation actually be faster? Using the squares
146 makes the numbers grow a lot! */
147 ec->tx_power += ((tx*tx - ec->tx_power) >> 5);
148
149 shift = 1;
150 /* Update the FIR taps */
151 offset2 = ec->curr_pos;
152 offset1 = ec->taps - offset2;
153 for (i = ec->taps - 1; i >= offset1; i--)
154 {
155 /* Leak to avoid the coefficients drifting beyond the ability of the
156 adaption process to bring them back under control. */
157 ec->fir_taps32[i] -= (ec->fir_taps32[i] >> 23);
158 ec->fir_taps32[i] += (ec->fir_state.history[i - offset1]*clean_rx) >> shift;
159 ec->fir_taps16[i] = (int16_t) (ec->fir_taps32[i] >> 15);
160 }
161 for ( ; i >= 0; i--)
162 {
163 ec->fir_taps32[i] -= (ec->fir_taps32[i] >> 23);
164 ec->fir_taps32[i] += (ec->fir_state.history[i + offset2]*clean_rx) >> shift;
165 ec->fir_taps16[i] = (int16_t) (ec->fir_taps32[i] >> 15);
166 }
167 }
168
169 /* Roll around the rolling buffer */
170 if (ec->curr_pos <= 0)
171 ec->curr_pos = ec->taps;
172 ec->curr_pos--;
173 return (int16_t) clean_rx;
174 }
175 /*- End of function --------------------------------------------------------*/
176 /*- End of file ------------------------------------------------------------*/

Repositories maintained by Peter Meerwald, pmeerw@pmeerw.net.