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/*
* gus_vol.c - Compute volume for GUS.
*
* Greg Lee 1993.
*/
#include "sound_config.h"
#ifndef EXCLUDE_GUS
#define GUS_VOLUME gus_wave_volume
extern int gus_wave_volume;
/*
* Calculate gus volume from note velocity, main volume, expression, and
* intrinsic patch volume given in patch library. Expression is multiplied
* in, so it emphasizes differences in note velocity, while main volume is
* added in -- I don't know whether this is right, but it seems reasonable to
* me. (In the previous stage, main volume controller messages were changed
* to expression controller messages, if they were found to be used for
* dynamic volume adjustments, so here, main volume can be assumed to be
* constant throughout a song.)
*
* Intrinsic patch volume is added in, but if over 64 is also multiplied in, so
* we can give a big boost to very weak voices like nylon guitar and the
* basses. The normal value is 64. Strings are assigned lower values.
*/
unsigned short
gus_adagio_vol (int vel, int mainv, int xpn, int voicev)
{
int i, m, n, x;
/*
* A voice volume of 64 is considered neutral, so adjust the main volume if
* something other than this neutral value was assigned in the patch
* library.
*/
x = 256 + 6 * (voicev - 64);
/*
* Boost expression by voice volume above neutral.
*/
if (voicev > 65)
xpn += voicev - 64;
xpn += (voicev - 64) / 2;
/*
* Combine multiplicative and level components.
*/
x = vel * xpn * 6 + (voicev / 4) * x;
#ifdef GUS_VOLUME
/*
* Further adjustment by installation-specific master volume control
* (default 60).
*/
x = (x * GUS_VOLUME * GUS_VOLUME) / 10000;
#endif
#ifdef GUS_USE_CHN_MAIN_VOLUME
/*
* Experimental support for the channel main volume
*/
mainv = (mainv / 2) + 64; /* Scale to 64 to 127 */
x = (x * mainv * mainv) / 16384;
#endif
if (x < 2)
return (0);
else if (x >= 65535)
return ((15 << 8) | 255);
/*
* Convert to gus's logarithmic form with 4 bit exponent i and 8 bit
* mantissa m.
*/
n = x;
i = 7;
if (n < 128)
{
while (i > 0 && n < (1 << i))
i--;
}
else
while (n > 255)
{
n >>= 1;
i++;
}
/*
* Mantissa is part of linear volume not expressed in exponent. (This is
* not quite like real logs -- I wonder if it's right.)
*/
m = x - (1 << i);
/*
* Adjust mantissa to 8 bits.
*/
if (m > 0)
{
if (i > 8)
m >>= i - 8;
else if (i < 8)
m <<= 8 - i;
}
return ((i << 8) + m);
}
#endif