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Diffstat (limited to '1.2-netsec/include/asterisk/plc.h')
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diff --git a/1.2-netsec/include/asterisk/plc.h b/1.2-netsec/include/asterisk/plc.h deleted file mode 100644 index a790ca167..000000000 --- a/1.2-netsec/include/asterisk/plc.h +++ /dev/null @@ -1,161 +0,0 @@ -/*! \file - * \brief SpanDSP - a series of DSP components for telephony - * - * plc.h - * - * \author Steve Underwood <steveu@coppice.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. - * This version is disclaimed to DIGIUM for inclusion in the Asterisk project. - */ - - -#if !defined(_PLC_H_) -#define _PLC_H_ - -#ifdef SOLARIS -#include <sys/int_types.h> -#else -#if defined(__OpenBSD__) || defined( __FreeBSD__) -#include <inttypes.h> -#else -#include <stdint.h> -#endif -#endif - -/*! \page plc_page Packet loss concealment -\section plc_page_sec_1 What does it do? -The packet loss concealment module provides a suitable synthetic fill-in signal, -to minimise the audible effect of lost packets in VoIP applications. It is not -tied to any particular codec, and could be used with almost any codec which does not -specify its own procedure for packet loss concealment. - -Where a codec specific concealment procedure exists, the algorithm is usually built -around knowledge of the characteristics of the particular codec. It will, therefore, -generally give better results for that particular codec than this generic concealer will. - -\section plc_page_sec_2 How does it work? -While good packets are being received, the plc_rx() routine keeps a record of the trailing -section of the known speech signal. If a packet is missed, plc_fillin() is called to produce -a synthetic replacement for the real speech signal. The average mean difference function -(AMDF) is applied to the last known good signal, to determine its effective pitch. -Based on this, the last pitch period of signal is saved. Essentially, this cycle of speech -will be repeated over and over until the real speech resumes. However, several refinements -are needed to obtain smooth pleasant sounding results. - -- The two ends of the stored cycle of speech will not always fit together smoothly. This can - cause roughness, or even clicks, at the joins between cycles. To soften this, the - 1/4 pitch period of real speech preceeding the cycle to be repeated is blended with the last - 1/4 pitch period of the cycle to be repeated, using an overlap-add (OLA) technique (i.e. - in total, the last 5/4 pitch periods of real speech are used). - -- The start of the synthetic speech will not always fit together smoothly with the tail of - real speech passed on before the erasure was identified. Ideally, we would like to modify - the last 1/4 pitch period of the real speech, to blend it into the synthetic speech. However, - it is too late for that. We could have delayed the real speech a little, but that would - require more buffer manipulation, and hurt the efficiency of the no-lost-packets case - (which we hope is the dominant case). Instead we use a degenerate form of OLA to modify - the start of the synthetic data. The last 1/4 pitch period of real speech is time reversed, - and OLA is used to blend it with the first 1/4 pitch period of synthetic speech. The result - seems quite acceptable. - -- As we progress into the erasure, the chances of the synthetic signal being anything like - correct steadily fall. Therefore, the volume of the synthesized signal is made to decay - linearly, such that after 50ms of missing audio it is reduced to silence. - -- When real speech resumes, an extra 1/4 pitch period of sythetic speech is blended with the - start of the real speech. If the erasure is small, this smoothes the transition. If the erasure - is long, and the synthetic signal has faded to zero, the blending softens the start up of the - real signal, avoiding a kind of "click" or "pop" effect that might occur with a sudden onset. - -\section plc_page_sec_3 How do I use it? -Before audio is processed, call plc_init() to create an instance of the packet loss -concealer. For each received audio packet that is acceptable (i.e. not including those being -dropped for being too late) call plc_rx() to record the content of the packet. Note this may -modify the packet a little after a period of packet loss, to blend real synthetic data smoothly. -When a real packet is not available in time, call plc_fillin() to create a sythetic substitute. -That's it! -*/ - -#define SAMPLE_RATE 8000 - -/*! Minimum allowed pitch (66 Hz) */ -#define PLC_PITCH_MIN 120 -/*! Maximum allowed pitch (200 Hz) */ -#define PLC_PITCH_MAX 40 -/*! Maximum pitch OLA window */ -#define PLC_PITCH_OVERLAP_MAX (PLC_PITCH_MIN >> 2) -/*! The length over which the AMDF function looks for similarity (20 ms) */ -#define CORRELATION_SPAN 160 -/*! 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. */ -#define PLC_HISTORY_LEN (CORRELATION_SPAN + PLC_PITCH_MIN) - -typedef struct -{ - /*! Consecutive erased samples */ - int missing_samples; - /*! Current offset into pitch period */ - int pitch_offset; - /*! Pitch estimate */ - int pitch; - /*! Buffer for a cycle of speech */ - float pitchbuf[PLC_PITCH_MIN]; - /*! History buffer */ - int16_t history[PLC_HISTORY_LEN]; - /*! Current pointer into the history buffer */ - int buf_ptr; -} plc_state_t; - - -#ifdef __cplusplus -extern "C" { -#endif - -/*! Process a block of received audio samples. - \brief Process a block of received audio samples. - \param s The packet loss concealer context. - \param amp The audio sample buffer. - \param len The number of samples in the buffer. - \return The number of samples in the buffer. */ -int plc_rx(plc_state_t *s, int16_t amp[], int len); - -/*! Fill-in a block of missing audio samples. - \brief Fill-in a block of missing audio samples. - \param s The packet loss concealer context. - \param amp The audio sample buffer. - \param len The number of samples to be synthesised. - \return The number of samples synthesized. */ -int plc_fillin(plc_state_t *s, int16_t amp[], int len); - -/*! Process a block of received V.29 modem audio samples. - \brief Process a block of received V.29 modem audio samples. - \param s The packet loss concealer context. - \return A pointer to the he packet loss concealer context. */ -plc_state_t *plc_init(plc_state_t *s); - -#ifdef __cplusplus -} -#endif - -#endif -/*- End of file ------------------------------------------------------------*/ |