From f63f6e749435108add1d34fdb1d08d722a9b80b6 Mon Sep 17 00:00:00 2001
From: Monty <xiphmont@xiph.org>
Date: Wed, 31 Jan 2001 23:58:49 +0000
Subject: [PATCH] Lower the highpass cutoff frequency a bit; midrange has
 preecho too. Also, look for preecho in the sides of the stereo image, so that
 the center does not dominate detection (eg, ringing hihat in the center).

Monty

svn path=/trunk/vorbis/; revision=1232
---
 lib/envelope.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 49 insertions(+), 7 deletions(-)

diff --git a/lib/envelope.c b/lib/envelope.c
index 259da31..4631dc1 100644
--- a/lib/envelope.c
+++ b/lib/envelope.c
@@ -12,7 +12,7 @@
  ********************************************************************
 
  function: PCM data envelope analysis and manipulation
- last mod: $Id: envelope.c,v 1.29 2001/01/22 01:38:24 xiphmont Exp $
+ last mod: $Id: envelope.c,v 1.30 2001/01/31 23:58:49 xiphmont Exp $
 
  Preecho calculation.
 
@@ -31,10 +31,6 @@
 #include "envelope.h"
 #include "misc.h"
 
-/* We use a Chebyshev bandbass for the preecho trigger bandpass; it's
-   close enough for sample rates 32000-48000 Hz (corner frequencies at
-   6k/14k assuming sample rate of 44.1kHz) */
-
 /* Digital filter designed by mkfilter/mkshape/gencode A.J. Fisher
    Command line: /www/usr/fisher/helpers/mkfilter -Ch \
    -6.0000000000e+00 -Bp -o 5 -a 1.3605442177e-01 3.1746031746e-01 -l */
@@ -57,6 +53,26 @@ static float cheb_bandpass_A[]={
   0.0303413711f};
 #endif 
 
+/* 4kHz Chebyshev highpass */
+static int    cheb_highpass_stages=10;
+static float cheb_highpass_gain= 1.314337427e+01f;
+/* z^-stage, z^-stage+1... */
+static float cheb_highpass_B[]={1.f,-10.f,45.f,-120.f,210.f,
+				-252.f,210.f,-120.f,45.f,-10.f,1.f};
+static float cheb_highpass_A[]={
+  -0.1013448254f,
+  0.4524819695f,
+  -1.3268091670f,
+  3.2875726855f,
+  -7.2782468961f,
+  13.0298867474f,
+  -17.6698599469f,
+  17.2757670409f,
+  -11.6207967046f,
+  4.8672119675f};
+
+#if 0
+/* 6kHz Chebyshev highpass */
 static int    cheb_highpass_stages=10;
 static float cheb_highpass_gain= 5.291963434e+01f;
 /* z^-stage, z^-stage+1... */
@@ -73,6 +89,7 @@ static float cheb_highpass_A[]={
   4.1950871291f,
   -4.2771757867f,
   2.3920318913f};
+#endif
 
 void _ve_envelope_init(envelope_lookup *e,vorbis_info *vi){
   codec_setup_info *ci=vi->codec_setup;
@@ -164,7 +181,8 @@ long _ve_envelope_search(vorbis_dsp_state *v,long searchpoint){
   vorbis_info *vi=v->vi;
   codec_setup_info *ci=vi->codec_setup;
   envelope_lookup *ve=((backend_lookup_state *)(v->backend_state))->ve;
-  long i,j;
+  long i,j,k;
+  float *work=alloca(sizeof(float)*ve->winlength*2);
 
   /* make sure we have enough storage to match the PCM */
   if(v->pcm_storage>ve->storage){
@@ -211,7 +229,31 @@ long _ve_envelope_search(vorbis_dsp_state *v,long searchpoint){
       }
       /*granulepos++;*/
     }
-    
+
+    /* look also for preecho in coupled channel pairs with the center
+       subtracted out (A-B) */
+    for(i=1;i<ve->ch;i+=2){
+      float *filteredA=ve->filtered[i-1]+j-ve->winlength;
+      float *filteredB=ve->filtered[i]+j-ve->winlength;
+      float m;
+
+      for(k=0;k<ve->winlength*2;k++)
+	work[k]=filteredA[k]-filteredB[k];
+
+      m=_ve_deltai(ve,work,work+ve->winlength);
+      
+      if(m>ci->preecho_thresh){
+	/*granulepos++;*/
+	return(0);
+      }
+      if(m<ci->postecho_thresh){
+	/*granulepos++;*/
+	return(0);
+      }
+      /*granulepos++;*/
+    }
+
+
     j+=min(ci->blocksizes[0],ve->winlength)/2;
 
     if(j>=searchpoint){
-- 
2.7.4