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PLC: Added lag windowing and constraint to synthesis energy

--- a/libcelt/celt.c

+++ b/libcelt/celt.c

@@ -54,6 +54,8 @@

 #include "float_cast.h"

 #include <stdarg.h>

+#define LPC_ORDER 24

+

 static const celt_word16 preemph = QCONST16(0.8f,15);

 #ifdef FIXED_POINT

@@ -1089,6 +1091,10 @@

    celt_word16 *oldBandE;

+#ifndef FIXED_POINT

+   celt_word16 *lpc;

+#endif

+

    int last_pitch_index;

    int loss_count;

 };

@@ -1163,9 +1169,16 @@

    st->preemph_memD = (celt_sig*)celt_alloc(C*sizeof(celt_sig));

+#ifndef FIXED_POINT

+   st->lpc = (celt_word16*)celt_alloc(C*LPC_ORDER*sizeof(celt_word16));

+#endif

+

    st->loss_count = 0;

    if ((st->decode_mem!=NULL) && (st->out_mem!=NULL) && (st->oldBandE!=NULL) &&

+#ifndef FIXED_POINT

+         (st->lpc!=NULL) &&

+#endif

        (st->preemph_memD!=NULL))

    {

       if (error)

@@ -1208,6 +1221,10 @@

    celt_free(st->decode_mem);

    celt_free(st->oldBandE);

    celt_free(st->preemph_memD);

+

+#ifndef FIXED_POINT

+   celt_free(st->lpc);

+#endif

    st->marker = DECODERFREED;

@@ -1217,7 +1234,6 @@

 #ifndef FIXED_POINT

 #include "plc.c"

 #endif

-#define LPC_ORDER 24

 static void celt_decode_lost(CELTDecoder * restrict st, celt_word16 * restrict pcm)

 {

    int c, N;

@@ -1271,18 +1287,30 @@

       float e[MAX_PERIOD];

       float exc[MAX_PERIOD];

       float ac[LPC_ORDER+1];

-      float lpc[LPC_ORDER];

       float decay = 1;

       celt_word32 mem[LPC_ORDER]={0};

       for (i=0;i<MAX_PERIOD;i++)

          exc[i] = st->out_mem[i*C+c];

-      _celt_autocorr(exc, ac, st->mode->window, st->mode->overlap,

-            LPC_ORDER, MAX_PERIOD);

-      ac[0] *= 1.0001;

-      _celt_lpc(lpc, ac, LPC_ORDER);

-      fir(exc, lpc, exc, MAX_PERIOD, LPC_ORDER, mem);

+      if (st->loss_count == 0)

+      {

+         _celt_autocorr(exc, ac, st->mode->window, st->mode->overlap,

+                        LPC_ORDER, MAX_PERIOD);

+

+         /* Noise floor -50 dB */

+         ac[0] *= 1.00001;

+         /* Lag windowing */

+         for (i=1;i<=LPC_ORDER;i++)

+         {

+            /*ac[i] *= exp(-.5*(2*M_PI*.002*i)*(2*M_PI*.002*i));*/

+            ac[i] -= ac[i]*(.008*i)*(.008*i);

+         }

+

+         _celt_lpc(st->lpc, ac, LPC_ORDER);

+      }

+      fir(exc, st->lpc, exc, MAX_PERIOD, LPC_ORDER, mem);

+

       /* Check if the waveform is decaying (and if so how fast) */

       {

          float E1=0, E2=0;

@@ -1301,6 +1329,7 @@

             decay = 1;

       }

+      float S1=0;

       /* Copy excitation, taking decay into account */

       for (i=0;i<len+st->mode->overlap;i++)

       {

@@ -1310,13 +1339,24 @@

             decay *= decay;

          }

          e[i] = decay*exc[offset+i];

+         S1 += st->out_mem[offset+i]*st->out_mem[offset+i];

       }

+      iir(e, st->lpc, e, len+st->mode->overlap, LPC_ORDER, mem);

+

+      {

+         float ratio, S2=0;

+         for (i=0;i<len+overlap;i++)

+            S2 += e[i]*e[i];

+         ratio = sqrt((S1+1)/(S2+1));

+         if (ratio < 1)

+            for (i=0;i<len+overlap;i++)

+               e[i] *= ratio;

+      }

+

       for (i=0;i<MAX_PERIOD+st->mode->overlap-N;i++)

          st->out_mem[C*i+c] = st->out_mem[C*(N+i)+c];

-      iir(e, lpc, e, len+st->mode->overlap, LPC_ORDER, mem);

-

       /* Apply TDAC to the concealed audio so that it blends with the

          previous and next frames */

       for (i=0;i<overlap/2;i++)

@@ -1338,17 +1378,7 @@

    }

 #endif

-   for (c=0;c<C;c++)

-   {

-      int j;

-      for (j=0;j<N;j++)

-      {

-         celt_sig tmp = MAC16_32_Q15(st->out_mem[C*(MAX_PERIOD-N)+C*j+c],

-                                preemph,st->preemph_memD[c]);

-         st->preemph_memD[c] = tmp;

-         pcm[C*j+c] = SCALEOUT(SIG2WORD16(tmp));

-      }

-   }

+   deemphasis(st->out_mem, pcm, N, C, preemph, st->preemph_memD);

    st->loss_count++;

--- a/libcelt/plc.c

+++ b/libcelt/plc.c

@@ -26,9 +26,9 @@

       for (j = 0; j < i; j++) 

          rr = SUB32(rr,MULT16_16(lpc[j],ac[i - j]));

 #ifdef FIXED_POINT

-      r = DIV32_16(rr+PSHR32(error,1),ADD16(error,8));

+      r = DIV32_16(rr+PSHR32(error,1),ADD16(error,1));

 #else

-      r = rr/(error+.003*ac[0]);

+      r = rr/(error+1e-15);

 #endif

       /*  Update LPC coefficients and total error */

       lpc[i] = r;

@@ -42,6 +42,8 @@

          lpc[j] = MAC16_16_P13(lpc[j],lpc[j],r);

       error = SUB16(error,MULT16_16_Q13(r,MULT16_16_Q13(error,r)));

+      if (error<.00001*ac[0])

+         break;

    }

    return error;

 }