/*
 *  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
 *
 *  $Id$
 *
 */


#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));
}

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