Asterisk.org: Developer Documentation (28 Oct 2009)

Wed Oct 28 15:47:55 2009

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# plc.c

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    00001 /*
    00002  * Asterisk -- An open source telephony toolkit.
    00003  *
    00004  * Written by Steve Underwood <steveu@coppice.org>
    00005  *
    00006  * Copyright (C) 2004 Steve Underwood
    00007  *
    00008  * All rights reserved.
    00009  *
    00010  * See http://www.asterisk.org for more information about
    00011  * the Asterisk project. Please do not directly contact
    00012  * any of the maintainers of this project for assistance;
    00013  * the project provides a web site, mailing lists and IRC
    00014  * channels for your use.
    00015  *
    00016  * This program is free software, distributed under the terms of
    00017  * the GNU General Public License Version 2. See the LICENSE file
    00018  * at the top of the source tree.
    00019  *
    00020  * This version may be optionally licenced under the GNU LGPL licence.
    00021  *
    00022  * A license has been granted to Digium (via disclaimer) for the use of
    00023  * this code.
    00024  */
    00025
    00026 /*! \file
    00027  *
    00028  * \brief SpanDSP - a series of DSP components for telephony
    00029  *
    00030  */
    00031
    00032 #include <stdio.h>
    00033 #include <stdlib.h>
    00034 #include <string.h>
    00035 #include <math.h>
    00036 #include <limits.h>
    00037
    00038 #include "asterisk.h"
    00039
    00040 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 34087 $")
    00041
    00042 #include "asterisk/plc.h"
    00043
    00044 #if !defined(FALSE)
    00045 #define FALSE 0
    00046 #endif
    00047 #if !defined(TRUE)
    00048 #define TRUE (!FALSE)
    00049 #endif
    00050
    00051 #if !defined(INT16_MAX)
    00052 #define INT16_MAX (32767)
    00053 #define INT16_MIN (-32767-1)
    00054 #endif
    00055
    00056 /* We do a straight line fade to zero volume in 50ms when we are filling in for missing data. */
    00057 #define ATTENUATION_INCREMENT       0.0025               /* Attenuation per sample */
    00058
    00059 #define ms_to_samples(t)       (((t)*SAMPLE_RATE)/1000)
    00060
    00061 static inline int16_t fsaturate(double damp)
    00062 {
    00063    if (damp > 32767.0)
    00064       return  INT16_MAX;
    00065    if (damp < -32768.0)
    00066       return  INT16_MIN;
    00067    return (int16_t) rint(damp);
    00068 }
    00069
    00070 static void save_history(plc_state_t *s, int16_t *buf, int len)
    00071 {
    00072    if (len >= PLC_HISTORY_LEN) {
    00073       /* Just keep the last part of the new data, starting at the beginning of the buffer */
    00074        memcpy(s->history, buf + len - PLC_HISTORY_LEN, sizeof(int16_t)*PLC_HISTORY_LEN);
    00075       s->buf_ptr = 0;
    00076       return;
    00077    }
    00078    if (s->buf_ptr + len > PLC_HISTORY_LEN) {
    00079       /* Wraps around - must break into two sections */
    00080       memcpy(s->history + s->buf_ptr, buf, sizeof(int16_t)*(PLC_HISTORY_LEN - s->buf_ptr));
    00081       len -= (PLC_HISTORY_LEN - s->buf_ptr);
    00082       memcpy(s->history, buf + (PLC_HISTORY_LEN - s->buf_ptr), sizeof(int16_t)*len);
    00083       s->buf_ptr = len;
    00084       return;
    00085    }
    00086    /* Can use just one section */
    00087    memcpy(s->history + s->buf_ptr, buf, sizeof(int16_t)*len);
    00088    s->buf_ptr += len;
    00089 }
    00090
    00091 /*- End of function --------------------------------------------------------*/
    00092
    00093 static void normalise_history(plc_state_t *s)
    00094 {
    00095    int16_t tmp[PLC_HISTORY_LEN];
    00096
    00097    if (s->buf_ptr == 0)
    00098       return;
    00099    memcpy(tmp, s->history, sizeof(int16_t)*s->buf_ptr);
    00100    memcpy(s->history, s->history + s->buf_ptr, sizeof(int16_t)*(PLC_HISTORY_LEN - s->buf_ptr));
    00101    memcpy(s->history + PLC_HISTORY_LEN - s->buf_ptr, tmp, sizeof(int16_t)*s->buf_ptr);
    00102    s->buf_ptr = 0;
    00103 }
    00104
    00105 /*- End of function --------------------------------------------------------*/
    00106
    00107 static int __inline__ amdf_pitch(int min_pitch, int max_pitch, int16_t amp[], int len)
    00108 {
    00109    int i;
    00110    int j;
    00111    int acc;
    00112    int min_acc;
    00113    int pitch;
    00114
    00115    pitch = min_pitch;
    00116    min_acc = INT_MAX;
    00117    for (i = max_pitch;  i <= min_pitch;  i++) {
    00118       acc = 0;
    00119       for (j = 0;  j < len;  j++)
    00120          acc += abs(amp[i + j] - amp[j]);
    00121       if (acc < min_acc) {
    00122          min_acc = acc;
    00123          pitch = i;
    00124       }
    00125    }
    00126    return pitch;
    00127 }
    00128
    00129 /*- End of function --------------------------------------------------------*/
    00130
    00131 int plc_rx(plc_state_t *s, int16_t amp[], int len)
    00132 {
    00133    int i;
    00134    int pitch_overlap;
    00135    float old_step;
    00136    float new_step;
    00137    float old_weight;
    00138    float new_weight;
    00139    float gain;
    00140
    00141    if (s->missing_samples) {
    00142       /* Although we have a real signal, we need to smooth it to fit well
    00143       with the synthetic signal we used for the previous block */
    00144
    00145       /* The start of the real data is overlapped with the next 1/4 cycle
    00146          of the synthetic data. */
    00147       pitch_overlap = s->pitch >> 2;
    00148       if (pitch_overlap > len)
    00149          pitch_overlap = len;
    00150       gain = 1.0 - s->missing_samples*ATTENUATION_INCREMENT;
    00151       if (gain < 0.0)
    00152          gain = 0.0;
    00153       new_step = 1.0/pitch_overlap;
    00154       old_step = new_step*gain;
    00155       new_weight = new_step;
    00156       old_weight = (1.0 - new_step)*gain;
    00157       for (i = 0;  i < pitch_overlap;  i++) {
    00158          amp[i] = fsaturate(old_weight*s->pitchbuf[s->pitch_offset] + new_weight*amp[i]);
    00159          if (++s->pitch_offset >= s->pitch)
    00160             s->pitch_offset = 0;
    00161          new_weight += new_step;
    00162          old_weight -= old_step;
    00163          if (old_weight < 0.0)
    00164             old_weight = 0.0;
    00165       }
    00166       s->missing_samples = 0;
    00167    }
    00168    save_history(s, amp, len);
    00169    return len;
    00170 }
    00171
    00172 /*- End of function --------------------------------------------------------*/
    00173
    00174 int plc_fillin(plc_state_t *s, int16_t amp[], int len)
    00175 {
    00176    int i;
    00177    int pitch_overlap;
    00178    float old_step;
    00179    float new_step;
    00180    float old_weight;
    00181    float new_weight;
    00182    float gain;
    00183    int16_t *orig_amp;
    00184    int orig_len;
    00185
    00186    orig_amp = amp;
    00187    orig_len = len;
    00188    if (s->missing_samples == 0) {
    00189       /* As the gap in real speech starts we need to assess the last known pitch,
    00190          and prepare the synthetic data we will use for fill-in */
    00191       normalise_history(s);
    00192       s->pitch = amdf_pitch(PLC_PITCH_MIN, PLC_PITCH_MAX, s->history + PLC_HISTORY_LEN - CORRELATION_SPAN - PLC_PITCH_MIN, CORRELATION_SPAN);
    00193       /* We overlap a 1/4 wavelength */
    00194       pitch_overlap = s->pitch >> 2;
    00195       /* Cook up a single cycle of pitch, using a single of the real signal with 1/4
    00196          cycle OLA'ed to make the ends join up nicely */
    00197       /* The first 3/4 of the cycle is a simple copy */
    00198       for (i = 0;  i < s->pitch - pitch_overlap;  i++)
    00199          s->pitchbuf[i] = s->history[PLC_HISTORY_LEN - s->pitch + i];
    00200       /* The last 1/4 of the cycle is overlapped with the end of the previous cycle */
    00201       new_step = 1.0/pitch_overlap;
    00202       new_weight = new_step;
    00203       for (  ;  i < s->pitch;  i++) {
    00204          s->pitchbuf[i] = s->history[PLC_HISTORY_LEN - s->pitch + i]*(1.0 - new_weight) + s->history[PLC_HISTORY_LEN - 2*s->pitch + i]*new_weight;
    00205          new_weight += new_step;
    00206       }
    00207       /* We should now be ready to fill in the gap with repeated, decaying cycles
    00208          of what is in pitchbuf */
    00209
    00210       /* We need to OLA the first 1/4 wavelength of the synthetic data, to smooth
    00211          it into the previous real data. To avoid the need to introduce a delay
    00212          in the stream, reverse the last 1/4 wavelength, and OLA with that. */
    00213       gain = 1.0;
    00214       new_step = 1.0/pitch_overlap;
    00215       old_step = new_step;
    00216       new_weight = new_step;
    00217       old_weight = 1.0 - new_step;
    00218       for (i = 0;  i < pitch_overlap;  i++) {
    00219          amp[i] = fsaturate(old_weight*s->history[PLC_HISTORY_LEN - 1 - i] + new_weight*s->pitchbuf[i]);
    00220          new_weight += new_step;
    00221          old_weight -= old_step;
    00222          if (old_weight < 0.0)
    00223             old_weight = 0.0;
    00224       }
    00225       s->pitch_offset = i;
    00226    } else {
    00227       gain = 1.0 - s->missing_samples*ATTENUATION_INCREMENT;
    00228       i = 0;
    00229    }
    00230    for (  ;  gain > 0.0  &&  i < len;  i++) {
    00231       amp[i] = s->pitchbuf[s->pitch_offset]*gain;
    00232       gain -= ATTENUATION_INCREMENT;
    00233       if (++s->pitch_offset >= s->pitch)
    00234          s->pitch_offset = 0;
    00235    }
    00236    for (  ;  i < len;  i++)
    00237       amp[i] = 0;
    00238    s->missing_samples += orig_len;
    00239    save_history(s, amp, len);
    00240    return len;
    00241 }
    00242
    00243 /*- End of function --------------------------------------------------------*/
    00244
    00245 plc_state_t *plc_init(plc_state_t *s)
    00246 {
    00247    memset(s, 0, sizeof(*s));
    00248    return s;
    00249 }
    00250 /*- End of function --------------------------------------------------------*/
    00251 /*- End of file ------------------------------------------------------------*/