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+/*---------------------------------------------------------------------------*\
+
+  FILE........: interp.c
+  AUTHOR......: David Rowe
+  DATE CREATED: 9/10/09
+
+  Interpolation of 20ms frames to 10ms frames.
+
+\*---------------------------------------------------------------------------*/
+
+/*
+  Copyright (C) 2009 David Rowe
+
+  All rights reserved.
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License version 2.1, as
+  published by the Free Software Foundation.  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 Lesser General Public License
+  along with this program; if not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <assert.h>
+#include <math.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "defines.h"
+#include "interp.h"
+#include "lsp.h"
+#include "quantise.h"
+
+float sample_log_amp(MODEL *model, float w);
+
+#if 0
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: interp()
+  AUTHOR......: David Rowe
+  DATE CREATED: 22/8/10
+
+  Given two frames decribed by model parameters 20ms apart, determines
+  the model parameters of the 10ms frame between them.  Assumes
+  voicing is available for middle (interpolated) frame.  Outputs are
+  amplitudes and Wo for the interpolated frame.
+
+  This version can interpolate the amplitudes between two frames of
+  different Wo and L.
+
+  This version works by log linear interpolation, but listening tests
+  showed it creates problems in background noise, e.g. hts2a and mmt1.
+  When this function is used (--dec mode) bg noise appears to be
+  amplitude modulated, and gets louder.  The interp_lsp() function
+  below seems to do a better job.
+
+\*---------------------------------------------------------------------------*/
+
+void interpolate(
+  MODEL *interp,    /* interpolated model params                     */
+  MODEL *prev,      /* previous frames model params                  */
+  MODEL *next,      /* next frames model params                      */
+  float Wo_min 
+)
+{
+    int   l;
+    float w,log_amp;
+
+    /* Wo depends on voicing of this and adjacent frames */
+
+    if (interp->voiced) {
+        if (prev->voiced && next->voiced)
+            interp->Wo = (prev->Wo + next->Wo)/2.0;
+        if (!prev->voiced && next->voiced)
+            interp->Wo = next->Wo;
+        if (prev->voiced && !next->voiced)
+            interp->Wo = prev->Wo;
+    }
+    else {
+        interp->Wo = Wo_min;
+    }
+    interp->L = PI/interp->Wo;
+
+    /* Interpolate amplitudes using linear interpolation in log domain */
+
+    for(l=1; l<=interp->L; l++) {
+        w = l*interp->Wo;
+        log_amp = (sample_log_amp(prev, w) + sample_log_amp(next, w))/2.0;
+        interp->A[l] = powf(10.0, log_amp);
+    }
+}
+#endif
+
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: sample_log_amp()
+  AUTHOR......: David Rowe
+  DATE CREATED: 22/8/10
+
+  Samples the amplitude envelope at an arbitrary frequency w.  Uses
+  linear interpolation in the log domain to sample between harmonic
+  amplitudes.
+
+\*---------------------------------------------------------------------------*/
+
+float sample_log_amp(MODEL *model, float w)
+{
+    int   m;
+    float f, log_amp;
+
+    assert(w > 0.0); assert (w <= PI);
+
+    m = floorf(w/model->Wo + 0.5);
+    f = (w - m*model->Wo)/w;
+    assert(f <= 1.0);
+
+    if (m < 1) {
+        log_amp = f*log10f(model->A[1] + 1E-6);
+    }
+    else if ((m+1) > model->L) {
+        log_amp = (1.0-f)*log10f(model->A[model->L] + 1E-6);
+    }
+    else {
+        log_amp = (1.0-f)*log10f(model->A[m] + 1E-6) +
+                  f*log10f(model->A[m+1] + 1E-6);
+    }
+
+    return log_amp;
+}
+
+#ifdef NOT_NEEDED
+
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: interp_lsp()
+  AUTHOR......: David Rowe
+  DATE CREATED: 10 Nov 2010
+
+  Given two frames decribed by model parameters 20ms apart, determines
+  the model parameters of the 10ms frame between them.  Assumes
+  voicing is available for middle (interpolated) frame.  Outputs are
+  amplitudes and Wo for the interpolated frame.
+
+  This version uses interpolation of LSPs, seems to do a better job
+  with bg noise.
+
+\*---------------------------------------------------------------------------*/
+
+void interpolate_lsp(
+  codec2_fft_cfg  fft_fwd_cfg,
+  MODEL *interp,      /* interpolated model params                     */
+  MODEL *prev,        /* previous frames model params                  */
+  MODEL *next,        /* next frames model params                      */
+  float *prev_lsps,   /* previous frames LSPs                          */
+  float  prev_e,      /* previous frames LPC energy                    */
+  float *next_lsps,   /* next frames LSPs                              */
+  float  next_e,      /* next frames LPC energy                        */
+  float *ak_interp,   /* interpolated aks for this frame               */
+  float *lsps_interp, /* interpolated lsps for this frame              */
+  float  Wo_min
+)
+{
+    int   i;
+    float e;
+    float snr;
+
+    /* trap corner case where V est is probably wrong */
+
+    if (interp->voiced && !prev->voiced && !next->voiced) {
+        interp->voiced = 0;
+    }
+
+    /* Wo depends on voicing of this and adjacent frames */
+
+    if (interp->voiced) {
+        if (prev->voiced && next->voiced)
+            interp->Wo = (prev->Wo + next->Wo)/2.0;
+        if (!prev->voiced && next->voiced)
+            interp->Wo = next->Wo;
+        if (prev->voiced && !next->voiced)
+            interp->Wo = prev->Wo;
+    }
+    else {
+        interp->Wo = Wo_min;
+    }
+    interp->L = PI/interp->Wo;
+
+    //printf("  interp: prev_v: %d next_v: %d prev_Wo: %f next_Wo: %f\n",
+    //     prev->voiced, next->voiced, prev->Wo, next->Wo);
+    //printf("  interp: Wo: %1.5f  L: %d\n", interp->Wo, interp->L);
+
+    /* interpolate LSPs */
+
+    for(i=0; i<LPC_ORD; i++) {
+        lsps_interp[i] = (prev_lsps[i] + next_lsps[i])/2.0;
+    }
+
+    /* Interpolate LPC energy in log domain */
+
+    e = powf(10.0, (log10f(prev_e) + log10f(next_e))/2.0);
+    //printf("  interp: e: %f\n", e);
+
+    /* convert back to amplitudes */
+
+    lsp_to_lpc(lsps_interp, ak_interp, LPC_ORD);
+    aks_to_M2(fft_fwd_cfg, ak_interp, LPC_ORD, interp, e, &snr, 0, 0, 1, 1, LPCPF_BETA, LPCPF_GAMMA);
+    //printf("  interp: ak[1]: %f A[1] %f\n", ak_interp[1], interp->A[1]);
+}
+#endif
+
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: interp_Wo()
+  AUTHOR......: David Rowe
+  DATE CREATED: 22 May 2012
+
+  Interpolates centre 10ms sample of Wo and L samples given two
+  samples 20ms apart. Assumes voicing is available for centre
+  (interpolated) frame.
+
+\*---------------------------------------------------------------------------*/
+
+void interp_Wo(
+  MODEL *interp,    /* interpolated model params                     */
+  MODEL *prev,      /* previous frames model params                  */
+  MODEL *next,      /* next frames model params                      */
+  float  Wo_min
+               )
+{
+    interp_Wo2(interp, prev, next, 0.5, Wo_min);
+}
+
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: interp_Wo2()
+  AUTHOR......: David Rowe
+  DATE CREATED: 22 May 2012
+
+  Weighted interpolation of two Wo samples.
+
+\*---------------------------------------------------------------------------*/
+
+void interp_Wo2(
+  MODEL *interp,    /* interpolated model params                     */
+  MODEL *prev,      /* previous frames model params                  */
+  MODEL *next,      /* next frames model params                      */
+  float  weight,
+  float  Wo_min
+)
+{
+    /* trap corner case where voicing est is probably wrong */
+
+    if (interp->voiced && !prev->voiced && !next->voiced) {
+        interp->voiced = 0;
+    }
+
+    /* Wo depends on voicing of this and adjacent frames */
+
+    if (interp->voiced) {
+        if (prev->voiced && next->voiced)
+            interp->Wo = (1.0 - weight)*prev->Wo + weight*next->Wo;
+        if (!prev->voiced && next->voiced)
+            interp->Wo = next->Wo;
+        if (prev->voiced && !next->voiced)
+            interp->Wo = prev->Wo;
+    }
+    else {
+        interp->Wo = Wo_min;
+    }
+    interp->L = PI/interp->Wo;
+}
+
+
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: interp_energy()
+  AUTHOR......: David Rowe
+  DATE CREATED: 22 May 2012
+
+  Interpolates centre 10ms sample of energy given two samples 20ms
+  apart.
+
+\*---------------------------------------------------------------------------*/
+
+float interp_energy(float prev_e, float next_e)
+{
+    //return powf(10.0, (log10f(prev_e) + log10f(next_e))/2.0);
+    return sqrtf(prev_e * next_e); //looks better is math. identical and faster math
+}
+
+
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: interp_energy2()
+  AUTHOR......: David Rowe
+  DATE CREATED: 22 May 2012
+
+  Interpolates centre 10ms sample of energy given two samples 20ms
+  apart.
+
+\*---------------------------------------------------------------------------*/
+
+float interp_energy2(float prev_e, float next_e, float weight)
+{
+    return POW10F((1.0 - weight)*log10f(prev_e) + weight*log10f(next_e));
+
+}
+
+
+/*---------------------------------------------------------------------------*\
+
+  FUNCTION....: interpolate_lsp_ver2()
+  AUTHOR......: David Rowe
+  DATE CREATED: 22 May 2012
+
+  Weighted interpolation of LSPs.
+
+\*---------------------------------------------------------------------------*/
+
+void interpolate_lsp_ver2(float interp[], float prev[],  float next[], float weight, int order)
+{
+    int i;
+
+    for(i=0; i<order; i++)
+        interp[i] = (1.0 - weight)*prev[i] + weight*next[i];
+}
+