SpanDSP - a series of DSP components for telephony. More...
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Data Structures | |
struct | plc_state_t |
Defines | |
#define | _PLC_H_ |
#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. | |
plc_state_t * | plc_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. |
SpanDSP - a series of DSP components for telephony.
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.
#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().
#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().
#define PLC_PITCH_MAX 40 |
#define PLC_PITCH_MIN 120 |
#define PLC_PITCH_OVERLAP_MAX (PLC_PITCH_MIN >> 2) |
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.
s | The packet loss concealer context. | |
amp | The audio sample buffer. | |
len | The number of samples to be synthesised. |
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.
s | The packet loss concealer context. |
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.
s | The packet loss concealer context. | |
amp | The audio sample buffer. | |
len | 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 }