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comparison spandsp-0.0.3/spandsp-0.0.3/src/echo.c @ 5:f762bf195c4b
import spandsp-0.0.3
author | Peter Meerwald <pmeerw@cosy.sbg.ac.at> |
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date | Fri, 25 Jun 2010 16:00:21 +0200 |
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1 /* | |
2 * SpanDSP - a series of DSP components for telephony | |
3 * | |
4 * echo.c - A line echo canceller. This code is being developed | |
5 * against and partially complies with G168. | |
6 * | |
7 * Written by Steve Underwood <steveu@coppice.org> | |
8 * and David Rowe <david_at_rowetel_dot_com> | |
9 * | |
10 * Copyright (C) 2001, 2003 Steve Underwood, 2007 David Rowe | |
11 * | |
12 * Based on a bit from here, a bit from there, eye of toad, ear of | |
13 * bat, 15 years of failed attempts by David and a few fried brain | |
14 * cells. | |
15 * | |
16 * All rights reserved. | |
17 * | |
18 * This program is free software; you can redistribute it and/or modify | |
19 * it under the terms of the GNU General Public License version 2, as | |
20 * published by the Free Software Foundation. | |
21 * | |
22 * This program is distributed in the hope that it will be useful, | |
23 * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
24 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
25 * GNU General Public License for more details. | |
26 * | |
27 * You should have received a copy of the GNU General Public License | |
28 * along with this program; if not, write to the Free Software | |
29 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
30 * | |
31 * $Id: echo.c,v 1.20 2006/12/01 18:00:48 steveu Exp $ | |
32 */ | |
33 | |
34 /*! \file */ | |
35 | |
36 /* Implementation Notes | |
37 David Rowe | |
38 April 2007 | |
39 | |
40 This code started life as Steve's NLMS algorithm with a tap | |
41 rotation algorithm to handle divergence during double talk. I | |
42 added a Geigel Double Talk Detector (DTD) [2] and performed some | |
43 G168 tests. However I had trouble meeting the G168 requirements, | |
44 especially for double talk - there were always cases where my DTD | |
45 failed, for example where near end speech was under the 6dB | |
46 threshold required for declaring double talk. | |
47 | |
48 So I tried a two path algorithm [1], which has so far given better | |
49 results. The original tap rotation/Geigel algorithm is available | |
50 in SVN http://svn.rowetel.com/software/oslec/tags/before_16bit. | |
51 It's probably possible to make it work if some one wants to put some | |
52 serious work into it. | |
53 | |
54 At present no special treatment is provided for tones, which | |
55 generally cause NLMS algorithms to diverge. Initial runs of a | |
56 subset of the G168 tests for tones (e.g ./echo_test 6) show the | |
57 current algorithm is passing OK, which is kind of surprising. The | |
58 full set of tests needs to be performed to confirm this result. | |
59 | |
60 One other interesting change is that I have managed to get the NLMS | |
61 code to work with 16 bit coefficients, rather than the original 32 | |
62 bit coefficents. This reduces the MIPs and storage required. | |
63 I evaulated the 16 bit port using g168_tests.sh and listening tests | |
64 on 4 real-world samples. | |
65 | |
66 I also attempted the implementation of a block based NLMS update | |
67 [2] but although this passes g168_tests.sh it didn't converge well | |
68 on the real-world samples. I have no idea why, perhaps a scaling | |
69 problem. The block based code is also available in SVN | |
70 http://svn.rowetel.com/software/oslec/tags/before_16bit. If this | |
71 code can be debugged, it will lead to further reduction in MIPS, as | |
72 the block update code maps nicely onto DSP instruction sets (it's a | |
73 dot product) compared to the current sample-by-sample update. | |
74 | |
75 Steve also has some nice notes on echo cancellers in echo.h | |
76 | |
77 | |
78 References: | |
79 | |
80 [1] Ochiai, Areseki, and Ogihara, "Echo Canceller with Two Echo | |
81 Path Models", IEEE Transactions on communications, COM-25, | |
82 No. 6, June | |
83 1977. | |
84 http://www.rowetel.com/images/echo/dual_path_paper.pdf | |
85 | |
86 [2] The classic, very useful paper that tells you how to | |
87 actually build a real world echo canceller: | |
88 Messerschmitt, Hedberg, Cole, Haoui, Winship, "Digital Voice | |
89 Echo Canceller with a TMS320020, | |
90 http://www.rowetel.com/images/echo/spra129.pdf | |
91 | |
92 [3] I have written a series of blog posts on this work, here is | |
93 Part 1: http://www.rowetel.com/blog/?p=18 | |
94 | |
95 [4] The source code http://svn.rowetel.com/software/oslec/ | |
96 | |
97 [5] A nice reference on LMS filters: | |
98 http://en.wikipedia.org/wiki/Least_mean_squares_filter | |
99 | |
100 Credits: | |
101 | |
102 Thanks to Steve Underwood, Jean-Marc Valin, and Ramakrishnan | |
103 Muthukrishnan for their suggestions and email discussions. Thanks | |
104 also to those people who collected echo samples for me such as | |
105 Mark, Pawel, and Pavel. | |
106 */ | |
107 | |
108 #ifdef HAVE_CONFIG_H | |
109 #include <config.h> | |
110 #endif | |
111 #ifdef __KERNEL__ | |
112 #include <linux/kernel.h> /* We're doing kernel work */ | |
113 #include <linux/module.h> | |
114 #include <linux/kernel.h> | |
115 #include <linux/slab.h> | |
116 #define malloc(a) kmalloc((a), GFP_KERNEL) | |
117 #define free(a) kfree(a) | |
118 #else | |
119 #include <stdio.h> | |
120 #include <stdlib.h> | |
121 #include <string.h> | |
122 #include <inttypes.h> | |
123 | |
124 #endif | |
125 | |
126 #include "spandsp/bit_operations.h" | |
127 #include "spandsp/echo.h" | |
128 | |
129 #if !defined(NULL) | |
130 #define NULL (void *) 0 | |
131 #endif | |
132 #if !defined(FALSE) | |
133 #define FALSE 0 | |
134 #endif | |
135 #if !defined(TRUE) | |
136 #define TRUE (!FALSE) | |
137 #endif | |
138 | |
139 #define MIN_TX_POWER_FOR_ADAPTION 64 | |
140 #define MIN_RX_POWER_FOR_ADAPTION 64 | |
141 #define DTD_HANGOVER 600 /* 600 samples, or 75ms */ | |
142 #define DC_LOG2BETA 3 /* log2() of DC filter Beta */ | |
143 | |
144 /*-----------------------------------------------------------------------*\ | |
145 | |
146 FUNCTIONS | |
147 | |
148 \*-----------------------------------------------------------------------*/ | |
149 | |
150 /* adapting coeffs using the traditional stochastic descent (N)LMS algorithm */ | |
151 | |
152 | |
153 #ifdef __BLACKFIN_ASM__ | |
154 static void __inline__ lms_adapt_bg(echo_can_state_t *ec, int clean, int shift) | |
155 { | |
156 int i, j; | |
157 int offset1; | |
158 int offset2; | |
159 int factor; | |
160 int exp; | |
161 int16_t *phist; | |
162 int n; | |
163 | |
164 if (shift > 0) | |
165 factor = clean << shift; | |
166 else | |
167 factor = clean >> -shift; | |
168 | |
169 /* Update the FIR taps */ | |
170 | |
171 offset2 = ec->curr_pos; | |
172 offset1 = ec->taps - offset2; | |
173 phist = &ec->fir_state_bg.history[offset2]; | |
174 | |
175 /* st: and en: help us locate the assembler in echo.s */ | |
176 | |
177 //asm("st:"); | |
178 n = ec->taps; | |
179 for (i = 0, j = offset2; i < n; i++, j++) | |
180 { | |
181 exp = *phist++ * factor; | |
182 ec->fir_taps16[1][i] += (int16_t) ((exp+(1<<14)) >> 15); | |
183 } | |
184 //asm("en:"); | |
185 | |
186 /* Note the asm for the inner loop above generated by Blackfin gcc | |
187 4.1.1 is pretty good (note even parallel instructions used): | |
188 | |
189 R0 = W [P0++] (X); | |
190 R0 *= R2; | |
191 R0 = R0 + R3 (NS) || | |
192 R1 = W [P1] (X) || | |
193 nop; | |
194 R0 >>>= 15; | |
195 R0 = R0 + R1; | |
196 W [P1++] = R0; | |
197 | |
198 A block based update algorithm would be much faster but the | |
199 above can't be improved on much. Every instruction saved in | |
200 the loop above is 2 MIPs/ch! The for loop above is where the | |
201 Blackfin spends most of it's time - about 17 MIPs/ch measured | |
202 with speedtest.c with 256 taps (32ms). Write-back and | |
203 Write-through cache gave about the same performance. | |
204 */ | |
205 } | |
206 | |
207 /* | |
208 IDEAS for further optimisation of lms_adapt_bg(): | |
209 | |
210 1/ The rounding is quite costly. Could we keep as 32 bit coeffs | |
211 then make filter pluck the MS 16-bits of the coeffs when filtering? | |
212 However this would lower potential optimisation of filter, as I | |
213 think the dual-MAC architecture requires packed 16 bit coeffs. | |
214 | |
215 2/ Block based update would be more efficient, as per comments above, | |
216 could use dual MAC architecture. | |
217 | |
218 3/ Look for same sample Blackfin LMS code, see if we can get dual-MAC | |
219 packing. | |
220 | |
221 4/ Execute the whole e/c in a block of say 20ms rather than sample | |
222 by sample. Processing a few samples every ms is inefficient. | |
223 */ | |
224 | |
225 #else | |
226 static __inline__ void lms_adapt_bg(echo_can_state_t *ec, int clean, int shift) | |
227 { | |
228 int i; | |
229 | |
230 int offset1; | |
231 int offset2; | |
232 int factor; | |
233 int exp; | |
234 | |
235 if (shift > 0) | |
236 factor = clean << shift; | |
237 else | |
238 factor = clean >> -shift; | |
239 | |
240 /* Update the FIR taps */ | |
241 | |
242 offset2 = ec->curr_pos; | |
243 offset1 = ec->taps - offset2; | |
244 | |
245 for (i = ec->taps - 1; i >= offset1; i--) | |
246 { | |
247 exp = (ec->fir_state_bg.history[i - offset1]*factor); | |
248 ec->fir_taps16[1][i] += (int16_t) ((exp+(1<<14)) >> 15); | |
249 } | |
250 for ( ; i >= 0; i--) | |
251 { | |
252 exp = (ec->fir_state_bg.history[i + offset2]*factor); | |
253 ec->fir_taps16[1][i] += (int16_t) ((exp+(1<<14)) >> 15); | |
254 } | |
255 } | |
256 #endif | |
257 | |
258 /*- End of function --------------------------------------------------------*/ | |
259 | |
260 echo_can_state_t *echo_can_create(int len, int adaption_mode) | |
261 { | |
262 echo_can_state_t *ec; | |
263 int i; | |
264 int j; | |
265 | |
266 ec = (echo_can_state_t *) malloc(sizeof(*ec)); | |
267 if (ec == NULL) | |
268 return NULL; | |
269 memset(ec, 0, sizeof(*ec)); | |
270 | |
271 ec->taps = len; | |
272 ec->log2taps = top_bit(len); | |
273 ec->curr_pos = ec->taps - 1; | |
274 | |
275 for (i = 0; i < 2; i++) | |
276 { | |
277 if ((ec->fir_taps16[i] = (int16_t *) malloc((ec->taps)*sizeof(int16_t))) == NULL) | |
278 { | |
279 for (j = 0; j < i; j++) | |
280 free(ec->fir_taps16[j]); | |
281 free(ec); | |
282 return NULL; | |
283 } | |
284 memset(ec->fir_taps16[i], 0, (ec->taps)*sizeof(int16_t)); | |
285 } | |
286 | |
287 fir16_create(&ec->fir_state, | |
288 ec->fir_taps16[0], | |
289 ec->taps); | |
290 fir16_create(&ec->fir_state_bg, | |
291 ec->fir_taps16[1], | |
292 ec->taps); | |
293 | |
294 for(i=0; i<5; i++) { | |
295 ec->xvtx[i] = ec->yvtx[i] = ec->xvrx[i] = ec->yvrx[i] = 0; | |
296 } | |
297 | |
298 ec->cng_level = 1000; | |
299 echo_can_adaption_mode(ec, adaption_mode); | |
300 | |
301 ec->snapshot = (int16_t*)malloc(ec->taps*sizeof(int16_t)); | |
302 memset(ec->snapshot, 0, sizeof(int16_t)*ec->taps); | |
303 | |
304 ec->cond_met = 0; | |
305 ec->Pstates = 0; | |
306 ec->Ltxacc = ec->Lrxacc = ec->Lcleanacc = ec->Lclean_bgacc = 0; | |
307 ec->Ltx = ec->Lrx = ec->Lclean = ec->Lclean_bg = 0; | |
308 ec->tx_1 = ec->tx_2 = ec->rx_1 = ec->rx_2 = 0; | |
309 ec->Lbgn = ec->Lbgn_acc = 0; | |
310 ec->Lbgn_upper = 200; | |
311 ec->Lbgn_upper_acc = ec->Lbgn_upper << 13; | |
312 | |
313 return ec; | |
314 } | |
315 /*- End of function --------------------------------------------------------*/ | |
316 | |
317 void echo_can_free(echo_can_state_t *ec) | |
318 { | |
319 int i; | |
320 | |
321 fir16_free(&ec->fir_state); | |
322 fir16_free(&ec->fir_state_bg); | |
323 for (i = 0; i < 2; i++) | |
324 free(ec->fir_taps16[i]); | |
325 free(ec->snapshot); | |
326 free(ec); | |
327 } | |
328 /*- End of function --------------------------------------------------------*/ | |
329 | |
330 void echo_can_adaption_mode(echo_can_state_t *ec, int adaption_mode) | |
331 { | |
332 ec->adaption_mode = adaption_mode; | |
333 } | |
334 /*- End of function --------------------------------------------------------*/ | |
335 | |
336 void echo_can_flush(echo_can_state_t *ec) | |
337 { | |
338 int i; | |
339 | |
340 ec->Ltxacc = ec->Lrxacc = ec->Lcleanacc = ec->Lclean_bgacc = 0; | |
341 ec->Ltx = ec->Lrx = ec->Lclean = ec->Lclean_bg = 0; | |
342 ec->tx_1 = ec->tx_2 = ec->rx_1 = ec->rx_2 = 0; | |
343 | |
344 ec->Lbgn = ec->Lbgn_acc = 0; | |
345 ec->Lbgn_upper = 200; | |
346 ec->Lbgn_upper_acc = ec->Lbgn_upper << 13; | |
347 | |
348 ec->nonupdate_dwell = 0; | |
349 | |
350 fir16_flush(&ec->fir_state); | |
351 fir16_flush(&ec->fir_state_bg); | |
352 ec->fir_state.curr_pos = ec->taps - 1; | |
353 ec->fir_state_bg.curr_pos = ec->taps - 1; | |
354 for (i = 0; i < 2; i++) | |
355 memset(ec->fir_taps16[i], 0, ec->taps*sizeof(int16_t)); | |
356 | |
357 ec->curr_pos = ec->taps - 1; | |
358 ec->Pstates = 0; | |
359 } | |
360 /*- End of function --------------------------------------------------------*/ | |
361 | |
362 void echo_can_snapshot(echo_can_state_t *ec) { | |
363 memcpy(ec->snapshot, ec->fir_taps16[0], ec->taps*sizeof(int16_t)); | |
364 } | |
365 /*- End of function --------------------------------------------------------*/ | |
366 | |
367 /* Dual Path Echo Canceller ------------------------------------------------*/ | |
368 | |
369 int16_t echo_can_update(echo_can_state_t *ec, int16_t tx, int16_t rx) | |
370 { | |
371 int32_t echo_value; | |
372 int clean_bg; | |
373 int tmp, tmp1; | |
374 | |
375 /* Input scaling was found be required to prevent problems when tx | |
376 starts clipping. Another possible way to handle this would be the | |
377 filter coefficent scaling. */ | |
378 | |
379 ec->tx = tx; ec->rx = rx; | |
380 tx >>=1; | |
381 rx >>=1; | |
382 | |
383 /* | |
384 Filter DC, 3dB point is 160Hz (I think), note 32 bit precision required | |
385 otherwise values do not track down to 0. Zero at DC, Pole at (1-Beta) | |
386 only real axis. Some chip sets (like Si labs) don't need | |
387 this, but something like a $10 X100P card does. Any DC really slows | |
388 down convergence. | |
389 | |
390 Note: removes some low frequency from the signal, this reduces | |
391 the speech quality when listening to samples through headphones | |
392 but may not be obvious through a telephone handset. | |
393 | |
394 Note that the 3dB frequency in radians is approx Beta, e.g. for | |
395 Beta = 2^(-3) = 0.125, 3dB freq is 0.125 rads = 159Hz. | |
396 */ | |
397 | |
398 if (ec->adaption_mode & ECHO_CAN_USE_RX_HPF) { | |
399 tmp = rx << 15; | |
400 #if 1 | |
401 /* Make sure the gain of the HPF is 1.0. This can still saturate a little under | |
402 impulse conditions, and it might roll to 32768 and need clipping on sustained peak | |
403 level signals. However, the scale of such clipping is small, and the error due to | |
404 any saturation should not markedly affect the downstream processing. */ | |
405 tmp -= (tmp >> 4); | |
406 #endif | |
407 ec->rx_1 += -(ec->rx_1>>DC_LOG2BETA) + tmp - ec->rx_2; | |
408 | |
409 /* hard limit filter to prevent clipping. Note that at this stage | |
410 rx should be limited to +/- 16383 due to right shift above */ | |
411 tmp1 = ec->rx_1 >> 15; | |
412 if (tmp1 > 16383) tmp1 = 16383; | |
413 if (tmp1 < -16383) tmp1 = -16383; | |
414 rx = tmp1; | |
415 ec->rx_2 = tmp; | |
416 } | |
417 | |
418 /* Block average of power in the filter states. Used for | |
419 adaption power calculation. */ | |
420 | |
421 { | |
422 int new, old; | |
423 | |
424 /* efficient "out with the old and in with the new" algorithm so | |
425 we don't have to recalculate over the whole block of | |
426 samples. */ | |
427 new = (int)tx * (int)tx; | |
428 old = (int)ec->fir_state.history[ec->fir_state.curr_pos] * | |
429 (int)ec->fir_state.history[ec->fir_state.curr_pos]; | |
430 ec->Pstates += ((new - old) + (1<<(ec->log2taps-1))) >> ec->log2taps; | |
431 if (ec->Pstates < 0) ec->Pstates = 0; | |
432 } | |
433 | |
434 /* Calculate short term average levels using simple single pole IIRs */ | |
435 | |
436 ec->Ltxacc += abs(tx) - ec->Ltx; | |
437 ec->Ltx = (ec->Ltxacc + (1<<4)) >> 5; | |
438 ec->Lrxacc += abs(rx) - ec->Lrx; | |
439 ec->Lrx = (ec->Lrxacc + (1<<4)) >> 5; | |
440 | |
441 /* Foreground filter ---------------------------------------------------*/ | |
442 | |
443 ec->fir_state.coeffs = ec->fir_taps16[0]; | |
444 echo_value = fir16(&ec->fir_state, tx); | |
445 ec->clean = rx - echo_value; | |
446 ec->Lcleanacc += abs(ec->clean) - ec->Lclean; | |
447 ec->Lclean = (ec->Lcleanacc + (1<<4)) >> 5; | |
448 | |
449 /* Background filter ---------------------------------------------------*/ | |
450 | |
451 echo_value = fir16(&ec->fir_state_bg, tx); | |
452 clean_bg = rx - echo_value; | |
453 ec->Lclean_bgacc += abs(clean_bg) - ec->Lclean_bg; | |
454 ec->Lclean_bg = (ec->Lclean_bgacc + (1<<4)) >> 5; | |
455 | |
456 /* Background Filter adaption -----------------------------------------*/ | |
457 | |
458 /* Almost always adap bg filter, just simple DT and energy | |
459 detection to minimise adaption in cases of strong double talk. | |
460 However this is not critical for the dual path algorithm. | |
461 */ | |
462 ec->factor = 0; | |
463 ec->shift = 0; | |
464 if ((ec->nonupdate_dwell == 0)) { | |
465 int P, logP, shift; | |
466 | |
467 /* Determine: | |
468 | |
469 f = Beta * clean_bg_rx/P ------ (1) | |
470 | |
471 where P is the total power in the filter states. | |
472 | |
473 The Boffins have shown that if we obey (1) we converge | |
474 quickly and avoid instability. | |
475 | |
476 The correct factor f must be in Q30, as this is the fixed | |
477 point format required by the lms_adapt_bg() function, | |
478 therefore the scaled version of (1) is: | |
479 | |
480 (2^30) * f = (2^30) * Beta * clean_bg_rx/P | |
481 factor = (2^30) * Beta * clean_bg_rx/P ----- (2) | |
482 | |
483 We have chosen Beta = 0.25 by experiment, so: | |
484 | |
485 factor = (2^30) * (2^-2) * clean_bg_rx/P | |
486 | |
487 (30 - 2 - log2(P)) | |
488 factor = clean_bg_rx 2 ----- (3) | |
489 | |
490 To avoid a divide we approximate log2(P) as top_bit(P), | |
491 which returns the position of the highest non-zero bit in | |
492 P. This approximation introduces an error as large as a | |
493 factor of 2, but the algorithm seems to handle it OK. | |
494 | |
495 Come to think of it a divide may not be a big deal on a | |
496 modern DSP, so its probably worth checking out the cycles | |
497 for a divide versus a top_bit() implementation. | |
498 */ | |
499 | |
500 P = MIN_TX_POWER_FOR_ADAPTION + ec->Pstates; | |
501 logP = top_bit(P) + ec->log2taps; | |
502 shift = 30 - 2 - logP; | |
503 ec->shift = shift; | |
504 | |
505 lms_adapt_bg(ec, clean_bg, shift); | |
506 } | |
507 | |
508 /* very simple DTD to make sure we dont try and adapt with strong | |
509 near end speech */ | |
510 | |
511 ec->adapt = 0; | |
512 if ((ec->Lrx > MIN_RX_POWER_FOR_ADAPTION) && (ec->Lrx > ec->Ltx)) | |
513 ec->nonupdate_dwell = DTD_HANGOVER; | |
514 if (ec->nonupdate_dwell) | |
515 ec->nonupdate_dwell--; | |
516 | |
517 /* Transfer logic ------------------------------------------------------*/ | |
518 | |
519 /* These conditions are from the dual path paper [1], I messed with | |
520 them a bit to improve performance. */ | |
521 | |
522 if ((ec->adaption_mode & ECHO_CAN_USE_ADAPTION) && | |
523 (ec->nonupdate_dwell == 0) && | |
524 (8*ec->Lclean_bg < 7*ec->Lclean) /* (ec->Lclean_bg < 0.875*ec->Lclean) */ && | |
525 (8*ec->Lclean_bg < ec->Ltx) /* (ec->Lclean_bg < 0.125*ec->Ltx) */ ) | |
526 { | |
527 if (ec->cond_met == 6) { | |
528 /* BG filter has had better results for 6 consecutive samples */ | |
529 ec->adapt = 1; | |
530 memcpy(ec->fir_taps16[0], ec->fir_taps16[1], ec->taps*sizeof(int16_t)); | |
531 } | |
532 else | |
533 ec->cond_met++; | |
534 } | |
535 else | |
536 ec->cond_met = 0; | |
537 | |
538 /* Non-Linear Processing ---------------------------------------------------*/ | |
539 | |
540 ec->clean_nlp = ec->clean; | |
541 if (ec->adaption_mode & ECHO_CAN_USE_NLP) | |
542 { | |
543 /* Non-linear processor - a fancy way to say "zap small signals, to avoid | |
544 residual echo due to (uLaw/ALaw) non-linearity in the channel.". */ | |
545 | |
546 if ((16*ec->Lclean < ec->Ltx)) | |
547 { | |
548 /* Our e/c has improved echo by at least 24 dB (each factor of 2 is 6dB, | |
549 so 2*2*2*2=16 is the same as 6+6+6+6=24dB) */ | |
550 if (ec->adaption_mode & ECHO_CAN_USE_CNG) | |
551 { | |
552 ec->cng_level = ec->Lbgn; | |
553 | |
554 /* Very elementary comfort noise generation. Just random | |
555 numbers rolled off very vaguely Hoth-like. DR: This | |
556 noise doesn't sound quite right to me - I suspect there | |
557 are some overlfow issues in the filtering as it's too | |
558 "crackly". TODO: debug this, maybe just play noise at | |
559 high level or look at spectrum. | |
560 */ | |
561 | |
562 ec->cng_rndnum = 1664525U*ec->cng_rndnum + 1013904223U; | |
563 ec->cng_filter = ((ec->cng_rndnum & 0xFFFF) - 32768 + 5*ec->cng_filter) >> 3; | |
564 ec->clean_nlp = (ec->cng_filter*ec->cng_level*8) >> 14; | |
565 | |
566 } | |
567 else if (ec->adaption_mode & ECHO_CAN_USE_CLIP) | |
568 { | |
569 /* This sounds much better than CNG */ | |
570 if (ec->clean_nlp > ec->Lbgn) | |
571 ec->clean_nlp = ec->Lbgn; | |
572 if (ec->clean_nlp < -ec->Lbgn) | |
573 ec->clean_nlp = -ec->Lbgn; | |
574 } | |
575 else | |
576 { | |
577 /* just mute the residual, doesn't sound very good, used mainly | |
578 in G168 tests */ | |
579 ec->clean_nlp = 0; | |
580 } | |
581 } | |
582 else { | |
583 /* Background noise estimator. I tried a few algorithms | |
584 here without much luck. This very simple one seems to | |
585 work best, we just average the level using a slow (1 sec | |
586 time const) filter if the current level is less than a | |
587 (experimentally derived) constant. This means we dont | |
588 include high level signals like near end speech. When | |
589 combined with CNG or especially CLIP seems to work OK. | |
590 */ | |
591 if (ec->Lclean < 40) { | |
592 ec->Lbgn_acc += abs(ec->clean) - ec->Lbgn; | |
593 ec->Lbgn = (ec->Lbgn_acc + (1<<11)) >> 12; | |
594 } | |
595 } | |
596 } | |
597 | |
598 /* Roll around the taps buffer */ | |
599 if (ec->curr_pos <= 0) | |
600 ec->curr_pos = ec->taps; | |
601 ec->curr_pos--; | |
602 | |
603 if (ec->adaption_mode & ECHO_CAN_DISABLE) | |
604 ec->clean_nlp = rx; | |
605 | |
606 /* Output scaled back up again to match input scaling */ | |
607 | |
608 return (int16_t) ec->clean_nlp << 1; | |
609 } | |
610 | |
611 /*- End of function --------------------------------------------------------*/ | |
612 | |
613 /* This function is seperated from the echo canceller is it is usually called | |
614 as part of the tx process. See rx HP (DC blocking) filter above, it's | |
615 the same design. | |
616 | |
617 Some soft phones send speech signals with a lot of low frequency | |
618 energy, e.g. down to 20Hz. This can make the hybrid non-linear | |
619 which causes the echo canceller to fall over. This filter can help | |
620 by removing any low frequency before it gets to the tx port of the | |
621 hybrid. | |
622 | |
623 It can also help by removing and DC in the tx signal. DC is bad | |
624 for LMS algorithms. | |
625 | |
626 This is one of the classic DC removal filters, adjusted to provide sufficient | |
627 bass rolloff to meet the above requirement to protect hybrids from things that | |
628 upset them. The difference between successive samples produces a lousy HPF, and | |
629 then a suitably placed pole flattens things out. The final result is a nicely | |
630 rolled off bass end. The filtering is implemented with extended fractional | |
631 precision, which noise shapes things, giving very clean DC removal. | |
632 */ | |
633 | |
634 int16_t echo_can_hpf_tx(echo_can_state_t *ec, int16_t tx) { | |
635 int tmp, tmp1; | |
636 | |
637 if (ec->adaption_mode & ECHO_CAN_USE_TX_HPF) { | |
638 tmp = tx << 15; | |
639 #if 1 | |
640 /* Make sure the gain of the HPF is 1.0. The first can still saturate a little under | |
641 impulse conditions, and it might roll to 32768 and need clipping on sustained peak | |
642 level signals. However, the scale of such clipping is small, and the error due to | |
643 any saturation should not markedly affect the downstream processing. */ | |
644 tmp -= (tmp >> 4); | |
645 #endif | |
646 ec->tx_1 += -(ec->tx_1>>DC_LOG2BETA) + tmp - ec->tx_2; | |
647 tmp1 = ec->tx_1 >> 15; | |
648 if (tmp1 > 32767) tmp1 = 32767; | |
649 if (tmp1 < -32767) tmp1 = -32767; | |
650 tx = tmp1; | |
651 ec->tx_2 = tmp; | |
652 } | |
653 | |
654 return tx; | |
655 } | |
656 | |
657 /*- End of function --------------------------------------------------------*/ | |
658 /*- End of file ------------------------------------------------------------*/ |