1 files changed, 79 insertions, 0 deletions
diff --git a/libtoolame-dab/ath.c b/libtoolame-dab/ath.c
new file mode 100644
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--- /dev/null
+++ b/libtoolame-dab/ath.c
@@ -0,0 +1,79 @@
+#include <stdio.h>
+#include <math.h>
+#include "common.h"
+#include "ath.h"
+
+  /* freq in hz */
+FLOAT8 ATH_dB(FLOAT8 f, FLOAT8 value)
+{
+  /* from Painter & Spanias
+    modified by Gabriel Bouvigne to better fit the reality
+  ath =    3.640 * pow(f,-0.8)
+         - 6.800 * exp(-0.6*pow(f-3.4,2.0))
+         + 6.000 * exp(-0.15*pow(f-8.7,2.0))
+         + 0.6* 0.001 * pow(f,4.0);
+
+
+  In the past LAME was using the Painter &Spanias formula.
+  But we had some recurrent problems with HF content.
+  We measured real ATH values, and found the older formula
+  to be inacurate in the higher part. So we made this new
+  formula and this solved most of HF problematic testcases.
+  The tradeoff is that in VBR mode it increases a lot the
+  bitrate.*/
+
+
+/*this curve can be udjusted according to the VBR scale:
+it adjusts from something close to Painter & Spanias
+on V9 up to Bouvigne's formula for V0. This way the VBR
+bitrate is more balanced according to the -V value.*/
+
+  FLOAT8 ath;
+  FLOAT8 valueold = 0.0;
+
+  if (f < -.3)
+      f=3410;
+
+  f /= 1000;  // convert to khz
+  f  = MAX(0.01, f);
+  f  = MIN(18.0, f);
+
+  ath =    3.640 * pow(f,-0.8)
+         - 6.800 * exp(-0.6*pow(f-3.4,2.0))
+         + 6.000 * exp(-0.15*pow(f-8.7,2.0))
+         + (0.6+0.04*valueold)* 0.001 * pow(f,4.0);
+
+  /* MFC Feb 2003
+     I've changed the fudge technique on the code.
+     The "-l [float]" value raises/lowers the ATH by this many dB */
+  return (ath + value);
+}
+
+
+/* Convert ATH values from dB into energy values as required by the psycho model */
+float ATH_energy(float freq, float value) {
+  float db;
+  db = ATH_dB(freq, 0) + value; // Originally: ATH_dB(freq,value)
+  /* The values in the standard, and from the ATH formula are in dB.
+     In the psycho model we are working in the energy domain. Hence the values that 
+     are in the absthr_X tables are not in dB. This function converts from dB into the energy domain.
+     As noted on the LAME mailing list from years ago (MFC FIX find the reference), the 
+     absolute threhsold of hearing values in the tables in the standard are dodgy - the
+     ATH in the tables do not correspond to any previously known values of the ATH. 
+     From ISO 11172 Tables D.4.x
+       "A value of 0dB represents a level in the absolute threshold calculation of
+        96dB below the energy of a sine wave of amplitude 32760."
+     But I still don't know why the factor of 41.837375 is the value that it is. MFC Feb 2003 */
+  return(pow(10.0, (db+41.837375)*0.1));
+}
+
+
+/* Convert a frequency (in Hz) to a bark value
+   Taken from LAME. MFC Feb 2003 
+   see for example "Zwicker: Psychoakustik, 1982; ISBN 3-540-11401-7 */
+FLOAT8 freq2bark(FLOAT8 freq)
+{
+    if (freq<0) freq=0;
+    freq = freq * 0.001;
+    return 13.0*atan(.76*freq) + 3.5*atan(freq*freq/(7.5*7.5));
+}