Move library tree where it belongs

lib-src/twolame/libtwolame/ath.c

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+/*
+ *  TwoLAME: an optimized MPEG Audio Layer Two encoder
+ *
+ *  Copyright (C) 2001-2004 Michael Cheng
+ *  Copyright (C) 2004-2006 The TwoLAME Project
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ *  $Id: ath.c,v 1.3 2008-02-01 19:44:27 richardash1981 Exp $
+ *
+ */
+
+
+#include <stdio.h>
+#include <math.h>
+
+#include "twolame.h"
+#include "common.h"
+#include "ath.h"
+
+
+/* freq in hz */
+FLOAT ath_db(FLOAT f, FLOAT 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.*/
+
+	FLOAT ath;
+	FLOAT 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 */
+FLOAT ath_freq2bark(FLOAT 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));
+}
+
+// vim:ts=4:sw=4:nowrap: