plc.h File Reference

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

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Data Structures
struct	plc_state_t

Macros
#define	CORRELATION_SPAN   160
#define	PLC_HISTORY_LEN   (CORRELATION_SPAN + PLC_PITCH_MIN)
#define	PLC_PITCH_MAX   40
#define	PLC_PITCH_MIN   120
#define	PLC_PITCH_OVERLAP_MAX   (PLC_PITCH_MIN >> 2)

Functions
int	plc_fillin (plc_state_t *s, int16_t amp[], int len)
	Fill-in a block of missing audio samples. More...
plc_state_t *	plc_init (plc_state_t *s)
	Process a block of received V.29 modem audio samples. More...
int	plc_rx (plc_state_t *s, int16_t amp[], int len)
	Process a block of received audio samples. More...

Detailed Description

SpanDSP - a series of DSP components for telephony.

plc.h

Author

Steve Underwood steve.nosp@m.u@co.nosp@m.ppice.nosp@m..org

Copyright (C) 2004 Steve Underwood

All rights reserved.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

This version may be optionally licenced under the GNU LGPL licence.

A license has been granted to Digium (via disclaimer) for the use of this code.

Definition in file plc.h.

Macro Definition Documentation

CORRELATION_SPAN

#define CORRELATION_SPAN   160

The length over which the AMDF function looks for similarity (20 ms)

Definition at line 99 of file plc.h.

Referenced by plc_fillin().

PLC_HISTORY_LEN

#define PLC_HISTORY_LEN   (CORRELATION_SPAN + PLC_PITCH_MIN)

History buffer length. The buffer much also be at leat 1.25 times PLC_PITCH_MIN, but that is much smaller than the buffer needs to be for the pitch assessment.

Definition at line 103 of file plc.h.

Referenced by normalise_history(), plc_fillin(), and save_history().

PLC_PITCH_MAX

#define PLC_PITCH_MAX   40

Maximum allowed pitch (200 Hz)

Definition at line 95 of file plc.h.

Referenced by plc_fillin().

PLC_PITCH_MIN

#define PLC_PITCH_MIN   120

Minimum allowed pitch (66 Hz)

Definition at line 93 of file plc.h.

Referenced by plc_fillin().

PLC_PITCH_OVERLAP_MAX

#define PLC_PITCH_OVERLAP_MAX   (PLC_PITCH_MIN >> 2)

Maximum pitch OLA window

Definition at line 97 of file plc.h.

Function Documentation

plc_fillin()

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, len(), 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().

{
   int i;
   int pitch_overlap;
   float old_step;
   float new_step;
   float old_weight;
   float new_weight;
   float gain;
   int orig_len;

   orig_len = len;
   if (s->missing_samples == 0) {
      /* As the gap in real speech starts we need to assess the last known pitch,
      and prepare the synthetic data we will use for fill-in */
      normalise_history(s);
      s->pitch = amdf_pitch(PLC_PITCH_MIN, PLC_PITCH_MAX, s->history + PLC_HISTORY_LEN - CORRELATION_SPAN - PLC_PITCH_MIN, CORRELATION_SPAN);
      /* We overlap a 1/4 wavelength */
      pitch_overlap = s->pitch >> 2;
      /* Cook up a single cycle of pitch, using a single of the real signal with 1/4
      cycle OLA'ed to make the ends join up nicely */
      /* The first 3/4 of the cycle is a simple copy */
      for (i = 0;  i < s->pitch - pitch_overlap;  i++)
         s->pitchbuf[i] = s->history[PLC_HISTORY_LEN - s->pitch + i];
      /* The last 1/4 of the cycle is overlapped with the end of the previous cycle */
      new_step = 1.0/pitch_overlap;
      new_weight = new_step;
      for ( ; i < s->pitch; i++) {
         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;
         new_weight += new_step;
      }
      /* We should now be ready to fill in the gap with repeated, decaying cycles
      of what is in pitchbuf */

      /* We need to OLA the first 1/4 wavelength of the synthetic data, to smooth
      it into the previous real data. To avoid the need to introduce a delay
      in the stream, reverse the last 1/4 wavelength, and OLA with that. */
      gain = 1.0;
      new_step = 1.0 / pitch_overlap;
      old_step = new_step;
      new_weight = new_step;
      old_weight = 1.0 - new_step;
      for (i = 0; i < pitch_overlap; i++) {
         amp[i] = fsaturate(old_weight * s->history[PLC_HISTORY_LEN - 1 - i] + new_weight * s->pitchbuf[i]);
         new_weight += new_step;
         old_weight -= old_step;
         if (old_weight < 0.0)
            old_weight = 0.0;
      }
      s->pitch_offset = i;
   } else {
      gain = 1.0 - s->missing_samples*ATTENUATION_INCREMENT;
      i = 0;
   }
   for ( ; gain > 0.0 && i < len; i++) {
      amp[i] = s->pitchbuf[s->pitch_offset] * gain;
      gain -= ATTENUATION_INCREMENT;
      if (++s->pitch_offset >= s->pitch)
         s->pitch_offset = 0;
   }
   for ( ; i < len; i++)
      amp[i] = 0;
   s->missing_samples += orig_len;
   save_history(s, amp, len);
   return len;
}

plc_init()

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.

{
   memset(s, 0, sizeof(*s));
   return s;
}

plc_rx()

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(), len(), 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().

{
   int i;
   int pitch_overlap;
   float old_step;
   float new_step;
   float old_weight;
   float new_weight;
   float gain;

   if (s->missing_samples) {
      /* Although we have a real signal, we need to smooth it to fit well
      with the synthetic signal we used for the previous block */

      /* The start of the real data is overlapped with the next 1/4 cycle
         of the synthetic data. */
      pitch_overlap = s->pitch >> 2;
      if (pitch_overlap > len)
         pitch_overlap = len;
      gain = 1.0 - s->missing_samples*ATTENUATION_INCREMENT;
      if (gain < 0.0)
         gain = 0.0;
      new_step = 1.0/pitch_overlap;
      old_step = new_step*gain;
      new_weight = new_step;
      old_weight = (1.0 - new_step)*gain;
      for (i = 0; i < pitch_overlap; i++) {
         amp[i] = fsaturate(old_weight * s->pitchbuf[s->pitch_offset] + new_weight * amp[i]);
         if (++s->pitch_offset >= s->pitch)
            s->pitch_offset = 0;
         new_weight += new_step;
         old_weight -= old_step;
         if (old_weight < 0.0)
            old_weight = 0.0;
      }
      s->missing_samples = 0;
   }
   save_history(s, amp, len);
   return len;
}