Mon Oct 8 12:39:26 2012

Asterisk developer's documentation


plc.c File Reference

SpanDSP - a series of DSP components for telephony. More...

#include "asterisk.h"
#include <math.h>
#include "asterisk/plc.h"

Go to the source code of this file.

Defines

#define ATTENUATION_INCREMENT   0.0025
#define FALSE   0
#define INT16_MAX   (32767)
#define INT16_MIN   (-32767-1)
#define ms_to_samples(t)   (((t)*DEFAULT_SAMPLE_RATE)/1000)
#define TRUE   (!FALSE)

Functions

static int __inline__ amdf_pitch (int min_pitch, int max_pitch, int16_t amp[], int len)
static int16_t fsaturate (double damp)
static void normalise_history (plc_state_t *s)
int plc_fillin (plc_state_t *s, int16_t amp[], int len)
 Fill-in a block of missing audio samples.
plc_state_tplc_init (plc_state_t *s)
 Process a block of received V.29 modem audio samples.
int plc_rx (plc_state_t *s, int16_t amp[], int len)
 Process a block of received audio samples.
static void save_history (plc_state_t *s, int16_t *buf, int len)


Detailed Description

SpanDSP - a series of DSP components for telephony.

Author:
Steve Underwood <steveu@coppice.org>

Definition in file plc.c.


Define Documentation

#define ATTENUATION_INCREMENT   0.0025

Definition at line 58 of file plc.c.

Referenced by plc_fillin(), and plc_rx().

#define FALSE   0

Definition at line 46 of file plc.c.

#define INT16_MAX   (32767)

Definition at line 53 of file plc.c.

#define INT16_MIN   (-32767-1)

Definition at line 54 of file plc.c.

#define ms_to_samples (  )     (((t)*DEFAULT_SAMPLE_RATE)/1000)

Definition at line 60 of file plc.c.

#define TRUE   (!FALSE)

Definition at line 49 of file plc.c.


Function Documentation

static int __inline__ amdf_pitch ( int  min_pitch,
int  max_pitch,
int16_t  amp[],
int  len 
) [static]

Definition at line 108 of file plc.c.

Referenced by plc_fillin().

00109 {
00110    int i;
00111    int j;
00112    int acc;
00113    int min_acc;
00114    int pitch;
00115 
00116    pitch = min_pitch;
00117    min_acc = INT_MAX;
00118    for (i = max_pitch; i <= min_pitch; i++) {
00119       acc = 0;
00120       for (j = 0; j < len; j++)
00121          acc += abs(amp[i + j] - amp[j]);
00122       if (acc < min_acc) {
00123          min_acc = acc;
00124          pitch = i;
00125       }
00126    }
00127    return pitch;
00128 }

static int16_t fsaturate ( double  damp  )  [inline, static]

Definition at line 62 of file plc.c.

References INT16_MAX, and INT16_MIN.

Referenced by plc_fillin(), and plc_rx().

00063 {
00064    if (damp > 32767.0)
00065       return  INT16_MAX;
00066    if (damp < -32768.0)
00067       return  INT16_MIN;
00068    return (int16_t) rint(damp);
00069 }

static void normalise_history ( plc_state_t s  )  [static]

Definition at line 94 of file plc.c.

References plc_state_t::buf_ptr, plc_state_t::history, and PLC_HISTORY_LEN.

Referenced by plc_fillin().

00095 {
00096    int16_t tmp[PLC_HISTORY_LEN];
00097 
00098    if (s->buf_ptr == 0)
00099       return;
00100    memcpy(tmp, s->history, sizeof(int16_t)*s->buf_ptr);
00101    memcpy(s->history, s->history + s->buf_ptr, sizeof(int16_t) * (PLC_HISTORY_LEN - s->buf_ptr));
00102    memcpy(s->history + PLC_HISTORY_LEN - s->buf_ptr, tmp, sizeof(int16_t) * s->buf_ptr);
00103    s->buf_ptr = 0;
00104 }

int plc_fillin ( plc_state_t s,
int16_t  amp[],
int  len 
)

Fill-in a block of missing audio samples.

Fill-in a block of missing audio samples.

Parameters:
s The packet loss concealer context.
amp The audio sample buffer.
len The number of samples to be synthesised.
Returns:
The number of samples synthesized.

Definition at line 175 of file plc.c.

References amdf_pitch(), ATTENUATION_INCREMENT, CORRELATION_SPAN, fsaturate(), plc_state_t::history, plc_state_t::missing_samples, normalise_history(), plc_state_t::pitch, plc_state_t::pitch_offset, plc_state_t::pitchbuf, PLC_HISTORY_LEN, PLC_PITCH_MAX, PLC_PITCH_MIN, and save_history().

Referenced by adjust_frame_for_plc().

00176 {
00177    int i;
00178    int pitch_overlap;
00179    float old_step;
00180    float new_step;
00181    float old_weight;
00182    float new_weight;
00183    float gain;
00184    int orig_len;
00185 
00186    orig_len = len;
00187    if (s->missing_samples == 0) {
00188       /* As the gap in real speech starts we need to assess the last known pitch,
00189          and prepare the synthetic data we will use for fill-in */
00190       normalise_history(s);
00191       s->pitch = amdf_pitch(PLC_PITCH_MIN, PLC_PITCH_MAX, s->history + PLC_HISTORY_LEN - CORRELATION_SPAN - PLC_PITCH_MIN, CORRELATION_SPAN);
00192       /* We overlap a 1/4 wavelength */
00193       pitch_overlap = s->pitch >> 2;
00194       /* Cook up a single cycle of pitch, using a single of the real signal with 1/4
00195          cycle OLA'ed to make the ends join up nicely */
00196       /* The first 3/4 of the cycle is a simple copy */
00197       for (i = 0;  i < s->pitch - pitch_overlap;  i++)
00198          s->pitchbuf[i] = s->history[PLC_HISTORY_LEN - s->pitch + i];
00199       /* The last 1/4 of the cycle is overlapped with the end of the previous cycle */
00200       new_step = 1.0/pitch_overlap;
00201       new_weight = new_step;
00202       for ( ; i < s->pitch; i++) {
00203          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;
00204          new_weight += new_step;
00205       }
00206       /* We should now be ready to fill in the gap with repeated, decaying cycles
00207          of what is in pitchbuf */
00208 
00209       /* We need to OLA the first 1/4 wavelength of the synthetic data, to smooth
00210          it into the previous real data. To avoid the need to introduce a delay
00211          in the stream, reverse the last 1/4 wavelength, and OLA with that. */
00212       gain = 1.0;
00213       new_step = 1.0 / pitch_overlap;
00214       old_step = new_step;
00215       new_weight = new_step;
00216       old_weight = 1.0 - new_step;
00217       for (i = 0; i < pitch_overlap; i++) {
00218          amp[i] = fsaturate(old_weight * s->history[PLC_HISTORY_LEN - 1 - i] + new_weight * s->pitchbuf[i]);
00219          new_weight += new_step;
00220          old_weight -= old_step;
00221          if (old_weight < 0.0)
00222             old_weight = 0.0;
00223       }
00224       s->pitch_offset = i;
00225    } else {
00226       gain = 1.0 - s->missing_samples*ATTENUATION_INCREMENT;
00227       i = 0;
00228    }
00229    for ( ; gain > 0.0 && i < len; i++) {
00230       amp[i] = s->pitchbuf[s->pitch_offset] * gain;
00231       gain -= ATTENUATION_INCREMENT;
00232       if (++s->pitch_offset >= s->pitch)
00233          s->pitch_offset = 0;
00234    }
00235    for ( ; i < len; i++)
00236       amp[i] = 0;
00237    s->missing_samples += orig_len;
00238    save_history(s, amp, len);
00239    return len;
00240 }

plc_state_t* plc_init ( plc_state_t s  ) 

Process a block of received V.29 modem audio samples.

Process a block of received V.29 modem audio samples.

Parameters:
s The packet loss concealer context.
Returns:
A pointer to the he packet loss concealer context.

Definition at line 244 of file plc.c.

00245 {
00246    memset(s, 0, sizeof(*s));
00247    return s;
00248 }

int plc_rx ( plc_state_t s,
int16_t  amp[],
int  len 
)

Process a block of received audio samples.

Process a block of received audio samples.

Parameters:
s The packet loss concealer context.
amp The audio sample buffer.
len The number of samples in the buffer.
Returns:
The number of samples in the buffer.

Definition at line 132 of file plc.c.

References ATTENUATION_INCREMENT, fsaturate(), plc_state_t::missing_samples, plc_state_t::pitch, plc_state_t::pitch_offset, plc_state_t::pitchbuf, and save_history().

Referenced by adjust_frame_for_plc().

00133 {
00134    int i;
00135    int pitch_overlap;
00136    float old_step;
00137    float new_step;
00138    float old_weight;
00139    float new_weight;
00140    float gain;
00141    
00142    if (s->missing_samples) {
00143       /* Although we have a real signal, we need to smooth it to fit well
00144       with the synthetic signal we used for the previous block */
00145 
00146       /* The start of the real data is overlapped with the next 1/4 cycle
00147          of the synthetic data. */
00148       pitch_overlap = s->pitch >> 2;
00149       if (pitch_overlap > len)
00150          pitch_overlap = len;
00151       gain = 1.0 - s->missing_samples*ATTENUATION_INCREMENT;
00152       if (gain < 0.0)
00153          gain = 0.0;
00154       new_step = 1.0/pitch_overlap;
00155       old_step = new_step*gain;
00156       new_weight = new_step;
00157       old_weight = (1.0 - new_step)*gain;
00158       for (i = 0; i < pitch_overlap; i++) {
00159          amp[i] = fsaturate(old_weight * s->pitchbuf[s->pitch_offset] + new_weight * amp[i]);
00160          if (++s->pitch_offset >= s->pitch)
00161             s->pitch_offset = 0;
00162          new_weight += new_step;
00163          old_weight -= old_step;
00164          if (old_weight < 0.0)
00165             old_weight = 0.0;
00166       }
00167       s->missing_samples = 0;
00168    }
00169    save_history(s, amp, len);
00170    return len;
00171 }

static void save_history ( plc_state_t s,
int16_t *  buf,
int  len 
) [static]

Definition at line 71 of file plc.c.

References plc_state_t::buf_ptr, plc_state_t::history, and PLC_HISTORY_LEN.

Referenced by plc_fillin(), and plc_rx().

00072 {
00073    if (len >= PLC_HISTORY_LEN) {
00074       /* Just keep the last part of the new data, starting at the beginning of the buffer */
00075        memcpy(s->history, buf + len - PLC_HISTORY_LEN, sizeof(int16_t) * PLC_HISTORY_LEN);
00076       s->buf_ptr = 0;
00077       return;
00078    }
00079    if (s->buf_ptr + len > PLC_HISTORY_LEN) {
00080       /* Wraps around - must break into two sections */
00081       memcpy(s->history + s->buf_ptr, buf, sizeof(int16_t) * (PLC_HISTORY_LEN - s->buf_ptr));
00082       len -= (PLC_HISTORY_LEN - s->buf_ptr);
00083       memcpy(s->history, buf + (PLC_HISTORY_LEN - s->buf_ptr), sizeof(int16_t)*len);
00084       s->buf_ptr = len;
00085       return;
00086    }
00087    /* Can use just one section */
00088    memcpy(s->history + s->buf_ptr, buf, sizeof(int16_t)*len);
00089    s->buf_ptr += len;
00090 }


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