From da9ca6a06f2d56401bdb923d3c3e8862b34bd14c Mon Sep 17 00:00:00 2001
From: Monty <xiphmont@xiph.org>
Date: Sat, 4 Nov 2000 10:24:15 +0000
Subject: Clamp IIR highpass in envelope code to zero below a threshhold to
 avoid underflow.

svn path=/branches/branch_beta3/vorbis/; revision=985
---
 lib/envelope.c |  3 ++-
 lib/iir.c      | 15 ++++++++++++---
 lib/iir.h      | 12 ++++++------
 3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/lib/envelope.c b/lib/envelope.c
index 720f9c4f..0914f1c3 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 1.23.2.3 2000/11/04 06:43:49 xiphmont Exp $
+ last mod: $Id: envelope.c,v 1.23.2.4 2000/11/04 10:24:15 xiphmont Exp $
 
  Preecho calculation.
 
@@ -174,6 +174,7 @@ long _ve_envelope_search(vorbis_dsp_state *v,long searchpoint){
     float *filtered=ve->filtered[i];
     float *pcm=v->pcm[i];
     IIR_state *iir=ve->iir+i;
+    IIR_clamp(iir,9e-15);
     
     for(j=ve->current;j<v->pcm_current;j++)
       filtered[j]=IIR_filter(iir,pcm[j]);
diff --git a/lib/iir.c b/lib/iir.c
index 44fe2470..4a336496 100644
--- a/lib/iir.c
+++ b/lib/iir.c
@@ -12,7 +12,7 @@
  ********************************************************************
 
   function: Direct Form I, II IIR filters, plus some specializations
-  last mod: $Id: iir.c,v 1.2.2.2 2000/11/04 06:43:50 xiphmont Exp $
+  last mod: $Id: iir.c,v 1.2.2.3 2000/11/04 10:24:15 xiphmont Exp $
 
  ********************************************************************/
 
@@ -32,7 +32,6 @@ void IIR_init(IIR_state *s,int stages,float gain, float *A, float *B){
   s->coeff_A=_ogg_malloc(stages*sizeof(float));
   s->coeff_B=_ogg_malloc((stages+1)*sizeof(float));
   s->z_A=_ogg_calloc(stages*2,sizeof(float));
-  s->z_B=_ogg_calloc(stages*2,sizeof(float));
 
   memcpy(s->coeff_A,A,stages*sizeof(float));
   memcpy(s->coeff_B,B,(stages+1)*sizeof(float));
@@ -43,7 +42,6 @@ void IIR_clear(IIR_state *s){
     free(s->coeff_A);
     free(s->coeff_B);
     free(s->z_A);
-    free(s->z_B);
     memset(s,0,sizeof(IIR_state));
   }
 }
@@ -67,6 +65,17 @@ float IIR_filter(IIR_state *s,float in){
   return(newB);
 }
 
+/* prevents ringing down to underflow */
+void IIR_clamp(IIR_state *s,float thresh){
+  float *zA=s->z_A+s->ring;
+  int i;
+  for(i=0;i<s->stages;i++)
+    if(fabs(zA[i])>=thresh)break;
+  
+  if(i<s->stages)
+    memset(s->z_A,0,sizeof(float)*s->stages*2);
+}
+
 /* this assumes the symmetrical structure of the feed-forward stage of
    a Chebyshev bandpass to save multiplies */
 float IIR_filter_ChebBand(IIR_state *s,float in){
diff --git a/lib/iir.h b/lib/iir.h
index 9fee1437..4664b38b 100644
--- a/lib/iir.h
+++ b/lib/iir.h
@@ -12,7 +12,7 @@
  ********************************************************************
 
   function: Direct Form I, II IIR filters, plus some specializations
-  last mod: $Id: iir.h,v 1.2.2.1 2000/11/04 06:21:44 xiphmont Exp $
+  last mod: $Id: iir.h,v 1.2.2.2 2000/11/04 10:24:15 xiphmont Exp $
 
  ********************************************************************/
 
@@ -24,14 +24,14 @@ typedef struct {
   float *coeff_A;
   float *coeff_B;
   float *z_A;
-  float *z_B;
   int ring;
   float gain;
 } IIR_state;
 
-void IIR_init(IIR_state *s,int stages,float gain, float *A, float *B);
-void IIR_clear(IIR_state *s);
-float IIR_filter(IIR_state *s,float in);
-float IIR_filter_ChebBand(IIR_state *s,float in);
+extern void IIR_init(IIR_state *s,int stages,float gain, float *A, float *B);
+extern void IIR_clear(IIR_state *s);
+extern float IIR_filter(IIR_state *s,float in);
+extern float IIR_filter_ChebBand(IIR_state *s,float in);
+extern void IIR_clamp(IIR_state *s,float thresh);
 
 #endif
-- 
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