[PATCH] Fixing incoherent mono lowpass

Hi

Regarding the bug I previously reported here :
http://sourceforge.net/tracker/?func=detail&atid=100290&aid=3498760&group_id=290 
<http://sourceforge.net/tracker/?func=detail&atid=100290&aid=3498760&group_id=290>
<http://www.hydrogenaudio.org/forums/index.php?showtopic=93864&st=0&gopid=788612>http://www.hydrogenaudio.org/forums/index.php?showtopic=93864

I wrote a small patch to fix it, it basically adds a third parameter to 
/optimum_bandwidth/ function to inform that the track is in mono/stereo 
and change the lowpass frequency calculation accordingly.

Here is the patch :

diff -rupN lame-3.99.5/libmp3lame/lame.c 
lame-3.99.5-lowpassfix/libmp3lame/lame.c
--- lame-3.99.5/libmp3lame/lame.c    2011-10-18 23:51:20.000000000 +0200
+++ lame-3.99.5-lowpassfix/libmp3lame/lame.c    2012-03-08 
20:33:53.981285364 +0100
@@ -191,11 +191,12 @@ lame_init_params_ppflt(lame_internal_fla


  static void
-optimum_bandwidth(double *const lowerlimit, double *const upperlimit, 
const unsigned bitrate)
+optimum_bandwidth(double *const lowerlimit, double *const upperlimit, 
const unsigned bitrate, const int stereo)
  {
  /*
   *  Input:
   *      bitrate     total bitrate in kbps
+ *      stereo      0 for mono channel calculation, non 0 for stereo
   *
   *   Output:
   *      lowerlimit: best lowpass frequency limit for input filter in Hz
@@ -228,8 +229,10 @@ optimum_bandwidth(double *const lowerlim
          {320, 20500}
      };

-
-    table_index = nearestBitrateFullIndex(bitrate);
+    if(stereo)
+        table_index = nearestBitrateFullIndex(bitrate);
+    else
+        table_index = nearestBitrateFullIndex(bitrate*2);

      (void) freq_map[table_index].bitrate;
      *lowerlimit = freq_map[table_index].lowpass;
@@ -711,11 +714,11 @@ lame_init_params(lame_global_flags * gfp

          switch (gfp->VBR) {
          case vbr_off:{
-                optimum_bandwidth(&lowpass, &highpass, gfp->brate);
+                optimum_bandwidth(&lowpass, &highpass, gfp->brate, 
gfp->mode!=MONO);
                  break;
              }
          case vbr_abr:{
-                optimum_bandwidth(&lowpass, &highpass, 
gfp->VBR_mean_bitrate_kbps);
+                optimum_bandwidth(&lowpass, &highpass, 
gfp->VBR_mean_bitrate_kbps, gfp->mode!=MONO);
                  break;
              }
          case vbr_rh:{
@@ -759,9 +762,6 @@ lame_init_params(lame_global_flags * gfp
              }
          }

-        if (gfp->mode == MONO && (gfp->VBR == vbr_off || gfp->VBR == 
vbr_abr))
-            lowpass *= 1.5;
-
          gfp->lowpassfreq = lowpass;
      }


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