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#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 */
FLOAT8 ATH_energy(FLOAT8 freq, FLOAT8 value) {
FLOAT 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));
}
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