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/*
* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
/******************************************************************
iLBC Speech Coder ANSI-C Source Code
WebRtcIlbcfix_SimpleLpcAnalysis.c
******************************************************************/
#include "modules/audio_coding/codecs/ilbc/simple_lpc_analysis.h"
#include "modules/audio_coding/codecs/ilbc/bw_expand.h"
#include "modules/audio_coding/codecs/ilbc/constants.h"
#include "modules/audio_coding/codecs/ilbc/defines.h"
#include "modules/audio_coding/codecs/ilbc/poly_to_lsf.h"
#include "modules/audio_coding/codecs/ilbc/window32_w32.h"
/*----------------------------------------------------------------*
* lpc analysis (subrutine to LPCencode)
*---------------------------------------------------------------*/
void WebRtcIlbcfix_SimpleLpcAnalysis(
int16_t *lsf, /* (o) lsf coefficients */
int16_t *data, /* (i) new block of speech */
IlbcEncoder *iLBCenc_inst
/* (i/o) the encoder state structure */
) {
int k;
int scale;
size_t is;
int16_t stability;
/* Stack based */
int16_t A[LPC_FILTERORDER + 1];
int32_t R[LPC_FILTERORDER + 1];
int16_t windowedData[BLOCKL_MAX];
int16_t rc[LPC_FILTERORDER];
is=LPC_LOOKBACK+BLOCKL_MAX-iLBCenc_inst->blockl;
WEBRTC_SPL_MEMCPY_W16(iLBCenc_inst->lpc_buffer+is,data,iLBCenc_inst->blockl);
/* No lookahead, last window is asymmetric */
for (k = 0; k < iLBCenc_inst->lpc_n; k++) {
is = LPC_LOOKBACK;
if (k < (iLBCenc_inst->lpc_n - 1)) {
/* Hanning table WebRtcIlbcfix_kLpcWin[] is in Q15-domain so the output is right-shifted 15 */
WebRtcSpl_ElementwiseVectorMult(windowedData, iLBCenc_inst->lpc_buffer, WebRtcIlbcfix_kLpcWin, BLOCKL_MAX, 15);
} else {
/* Hanning table WebRtcIlbcfix_kLpcAsymWin[] is in Q15-domain so the output is right-shifted 15 */
WebRtcSpl_ElementwiseVectorMult(windowedData, iLBCenc_inst->lpc_buffer+is, WebRtcIlbcfix_kLpcAsymWin, BLOCKL_MAX, 15);
}
/* Compute autocorrelation */
WebRtcSpl_AutoCorrelation(windowedData, BLOCKL_MAX, LPC_FILTERORDER, R, &scale);
/* Window autocorrelation vector */
WebRtcIlbcfix_Window32W32(R, R, WebRtcIlbcfix_kLpcLagWin, LPC_FILTERORDER + 1 );
/* Calculate the A coefficients from the Autocorrelation using Levinson Durbin algorithm */
stability=WebRtcSpl_LevinsonDurbin(R, A, rc, LPC_FILTERORDER);
/*
Set the filter to {1.0, 0.0, 0.0,...} if filter from Levinson Durbin algorithm is unstable
This should basically never happen...
*/
if (stability!=1) {
A[0]=4096;
WebRtcSpl_MemSetW16(&A[1], 0, LPC_FILTERORDER);
}
/* Bandwidth expand the filter coefficients */
WebRtcIlbcfix_BwExpand(A, A, (int16_t*)WebRtcIlbcfix_kLpcChirpSyntDenum, LPC_FILTERORDER+1);
/* Convert from A to LSF representation */
WebRtcIlbcfix_Poly2Lsf(lsf + k*LPC_FILTERORDER, A);
}
is=LPC_LOOKBACK+BLOCKL_MAX-iLBCenc_inst->blockl;
WEBRTC_SPL_MEMCPY_W16(iLBCenc_inst->lpc_buffer,
iLBCenc_inst->lpc_buffer+LPC_LOOKBACK+BLOCKL_MAX-is, is);
return;
}