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annotate spandsp-0.0.6pre17/src/spandsp/dc_restore.h @ 4:26cd8f1ef0b1

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import spandsp-0.0.6pre17
author Peter Meerwald <pmeerw@cosy.sbg.ac.at>
date Fri, 25 Jun 2010 15:50:58 +0200
parents
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26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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1 /*
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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2 * SpanDSP - a series of DSP components for telephony
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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3 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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4 * dc_restore.h - General telephony routines to restore the zero D.C.
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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5 * level to audio which has a D.C. bias.
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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6 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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7 * Written by Steve Underwood <steveu@coppice.org>
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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8 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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9 * Copyright (C) 2001 Steve Underwood
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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10 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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11 * All rights reserved.
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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12 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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13 * This program is free software; you can redistribute it and/or modify
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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14 * it under the terms of the GNU Lesser General Public License version 2.1,
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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15 * as published by the Free Software Foundation.
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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16 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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17 * This program is distributed in the hope that it will be useful,
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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20 * GNU Lesser General Public License for more details.
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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21 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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22 * You should have received a copy of the GNU Lesser General Public
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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23 * License along with this program; if not, write to the Free Software
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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24 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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25 *
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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26 * $Id: dc_restore.h,v 1.24 2008/09/19 14:02:05 steveu Exp $
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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27 */
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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28
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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29 /*! \file */
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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30
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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31 #if !defined(_SPANDSP_DC_RESTORE_H_)
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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32 #define _SPANDSP_DC_RESTORE_H_
26cd8f1ef0b1 import spandsp-0.0.6pre17
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33
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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34 /*! \page dc_restore_page Removing DC bias from a signal
26cd8f1ef0b1 import spandsp-0.0.6pre17
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35
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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36 \section dc_restore_page_sec_1 What does it do?
26cd8f1ef0b1 import spandsp-0.0.6pre17
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37
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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38 Telecoms signals often contain considerable DC, but DC upsets a lot of signal
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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39 processing functions. Placing a zero DC restorer at the front of the processing
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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40 chain can often simplify the downstream processing.
26cd8f1ef0b1 import spandsp-0.0.6pre17
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41
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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42 \section dc_restore_page_sec_2 How does it work?
26cd8f1ef0b1 import spandsp-0.0.6pre17
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43
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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44 The DC restorer uses a leaky integrator to provide a long-ish term estimate of
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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45 the DC bias in the signal. A 32 bit estimate is used for the 16 bit audio, so
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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46 the noise introduced by the estimation can be keep in the lower bits, and the 16
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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47 bit DC value, which is subtracted from the signal, is fairly clean. The
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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48 following code fragment shows the algorithm used. dc_bias is a 32 bit integer,
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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49 while the sample and the resulting clean_sample are 16 bit integers.
26cd8f1ef0b1 import spandsp-0.0.6pre17
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50
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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51 dc_bias += ((((int32_t) sample << 15) - dc_bias) >> 14);
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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52 clean_sample = sample - (dc_bias >> 15);
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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53 */
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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54
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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55 /*!
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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56 Zero DC restoration descriptor. This defines the working state for a single
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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57 instance of DC content filter.
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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58 */
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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59 typedef struct
26cd8f1ef0b1 import spandsp-0.0.6pre17
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60 {
26cd8f1ef0b1 import spandsp-0.0.6pre17
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61 int32_t state;
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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62 } dc_restore_state_t;
26cd8f1ef0b1 import spandsp-0.0.6pre17
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63
26cd8f1ef0b1 import spandsp-0.0.6pre17
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64 #if defined(__cplusplus)
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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65 extern "C"
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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66 {
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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67 #endif
26cd8f1ef0b1 import spandsp-0.0.6pre17
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68
26cd8f1ef0b1 import spandsp-0.0.6pre17
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69 static __inline__ void dc_restore_init(dc_restore_state_t *dc)
26cd8f1ef0b1 import spandsp-0.0.6pre17
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70 {
26cd8f1ef0b1 import spandsp-0.0.6pre17
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71 dc->state = 0;
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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72 }
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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73 /*- End of function --------------------------------------------------------*/
26cd8f1ef0b1 import spandsp-0.0.6pre17
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74
26cd8f1ef0b1 import spandsp-0.0.6pre17
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75 static __inline__ int16_t dc_restore(dc_restore_state_t *dc, int16_t sample)
26cd8f1ef0b1 import spandsp-0.0.6pre17
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76 {
26cd8f1ef0b1 import spandsp-0.0.6pre17
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77 dc->state += ((((int32_t) sample << 15) - dc->state) >> 14);
26cd8f1ef0b1 import spandsp-0.0.6pre17
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78 return (int16_t) (sample - (dc->state >> 15));
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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79 }
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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80 /*- End of function --------------------------------------------------------*/
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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81
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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82 static __inline__ int16_t dc_restore_estimate(dc_restore_state_t *dc)
26cd8f1ef0b1 import spandsp-0.0.6pre17
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83 {
26cd8f1ef0b1 import spandsp-0.0.6pre17
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84 return (int16_t) (dc->state >> 15);
26cd8f1ef0b1 import spandsp-0.0.6pre17
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85 }
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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86 /*- End of function --------------------------------------------------------*/
26cd8f1ef0b1 import spandsp-0.0.6pre17
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87
26cd8f1ef0b1 import spandsp-0.0.6pre17
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88 #if defined(__cplusplus)
26cd8f1ef0b1 import spandsp-0.0.6pre17
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89 }
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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90 #endif
26cd8f1ef0b1 import spandsp-0.0.6pre17
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91
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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92 #endif
26cd8f1ef0b1 import spandsp-0.0.6pre17
Peter Meerwald <pmeerw@cosy.sbg.ac.at>
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93 /*- End of file ------------------------------------------------------------*/

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