shithub: libopusenc

Info  •  Files  •  Log  •  Branches

Adds windowing to the LPC output

--- a/src/opusenc.c

+++ b/src/opusenc.c

@@ -50,6 +50,8 @@

 #define LPC_PADDING 120

 #define LPC_ORDER 24

 #define LPC_INPUT 480

+/* Make the following constant always equal to 2*cos(M_PI/LPC_PADDING) */

+#define LPC_GOERTZEL_CONST 1.99931465f

 /* Allow up to 2 seconds for delayed decision. */

 #define MAX_LOOKAHEAD 96000

@@ -622,7 +624,6 @@

   int pad_samples = 3000;

   if (!enc->streams->stream_is_init) init_stream(enc);

   shift_buffer(enc);

-  /* FIXME: Do LPC extension instead. */

   memset(&enc->buffer[enc->channels*enc->buffer_end], 0, pad_samples*enc->channels*sizeof(enc->buffer[0]));

   extend_signal(&enc->buffer[enc->channels*enc->buffer_end], enc->buffer_end, LPC_PADDING, enc->channels);

   enc->decision_delay = 0;

@@ -866,6 +867,9 @@

 static void extend_signal(float *x, int before, int after, int channels) {

   int c;

+  int i;

+  float window[LPC_PADDING];

+  if (after==0) return;

   before = MIN(before, LPC_INPUT);

   if (before < 4*LPC_ORDER) {

     int i;

@@ -872,8 +876,19 @@

     for (i=0;i<after*channels;i++) x[i] = 0;

     return;

   }

+  {

+    /* Generate Window using a resonating IIR aka Goertzel's algorithm. */

+    float m0=1, m1=1;

+    float a1 = LPC_GOERTZEL_CONST;

+    window[0] = 1;

+    for (i=1;i<LPC_PADDING;i++) {

+      window[i] = a1*m0 - m1;

+      m1 = m0;

+      m0 = window[i];

+    }

+    for (i=0;i<LPC_PADDING;i++) window[i] = .5+.5*window[i];

+  }

   for (c=0;c<channels;c++) {

-    int i;

     float lpc[LPC_ORDER];

     vorbis_lpc_from_data(x-channels*before+c, lpc, before, channels);

     for (i=0;i<after;i++) {

@@ -883,6 +898,7 @@

       for (j=0;j<LPC_ORDER;j++) sum -= x[(i-j-1)*channels + c]*lpc[j];

       x[i*channels + c] = sum;

     }

+    for (i=0;i<after;i++) x[i*channels + c] *= window[i];

   }

 }

@@ -930,13 +946,18 @@

     aut[j]=d;

   }

-  /* FIXME: Apply lag windowing (better than bandwidth expansion) */

+  /* Apply lag windowing (better than bandwidth expansion) */

+  if (LPC_ORDER <= 32) {

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

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

+      aut[i] -= aut[i]*(0.008f*0.008f)*i*i;

+    }

+  }

   /* Generate lpc coefficients from autocorr values */

-  /* FIXME: This noise floor is insane! */

   /* set our noise floor to about -100dB */

-  error=aut[0] * (1. + 1e-10);

-  epsilon=1e-9*aut[0]+1e-10;

+  error=aut[0] * (1. + 1e-7);

+  epsilon=1e-6*aut[0]+1e-7;

   for(i=0;i<LPC_ORDER;i++){

     double r= -aut[i+1];

@@ -973,7 +994,7 @@

   /* slightly damp the filter */

   {

-    double g = .99;

+    double g = .999;

     double damp = g;

     for(j=0;j<LPC_ORDER;j++){

       lpc[j]*=damp;