drivers/sound/gus

/* */
This source file includes following definitions.
gus_adagio_vol
   1 /*
   2  * gus_vol.c - Compute volume for GUS.
   3  * 
   4  * Greg Lee 1993.
   5  */
   6 #include "sound_config.h"
   7 #ifndef EXCLUDE_GUS
   8 
   9 #define GUS_VOLUME      gus_wave_volume
  10 
  11 
  12 extern int      gus_wave_volume;
  13 
  14 /*
  15  * Calculate gus volume from note velocity, main volume, expression, and
  16  * intrinsic patch volume given in patch library.  Expression is multiplied
  17  * in, so it emphasizes differences in note velocity, while main volume is
  18  * added in -- I don't know whether this is right, but it seems reasonable to
  19  * me.  (In the previous stage, main volume controller messages were changed
  20  * to expression controller messages, if they were found to be used for
  21  * dynamic volume adjustments, so here, main volume can be assumed to be
  22  * constant throughout a song.)
  23  * 
  24  * Intrinsic patch volume is added in, but if over 64 is also multiplied in, so
  25  * we can give a big boost to very weak voices like nylon guitar and the
  26  * basses.  The normal value is 64.  Strings are assigned lower values.
  27  */
  28 unsigned short
  29 gus_adagio_vol (int vel, int mainv, int xpn, int voicev)
     /*  */
  30 {
  31   int             i, m, n, x;
  32 
  33 
  34   /*
  35    * A voice volume of 64 is considered neutral, so adjust the main volume if
  36    * something other than this neutral value was assigned in the patch
  37    * library.
  38    */
  39   x = 256 + 6 * (voicev - 64);
  40 
  41   /* Boost expression by voice volume above neutral. */
  42   if (voicev > 65)
  43     xpn += voicev - 64;
  44   xpn += (voicev - 64) / 2;
  45 
  46   /* Combine multiplicative and level components. */
  47   x = vel * xpn * 6 + (voicev / 4) * x;
  48 
  49 #ifdef GUS_VOLUME
  50   /*
  51    * Further adjustment by installation-specific master volume control
  52    * (default 50).
  53    */
  54   x = (x * GUS_VOLUME * GUS_VOLUME) / 10000;
  55 #endif
  56 
  57   if (x < (1 << 11))
  58     return (11 << 8);
  59   else if (x >= 65535)
  60     return ((15 << 8) | 255);
  61 
  62   /*
  63    * Convert to gus's logarithmic form with 4 bit exponent i and 8 bit
  64    * mantissa m.
  65    */
  66   n = x;
  67   i = 7;
  68   if (n < 128)
  69     {
  70       while (i > 0 && n < (1 << i))
  71         i--;
  72     }
  73   else
  74     while (n > 255)
  75       {
  76         n >>= 1;
  77         i++;
  78       }
  79   /*
  80    * Mantissa is part of linear volume not expressed in exponent.  (This is
  81    * not quite like real logs -- I wonder if it's right.)
  82    */
  83   m = x - (1 << i);
  84 
  85   /* Adjust mantissa to 8 bits. */
  86   if (m > 0)
  87     {
  88       if (i > 8)
  89         m >>= i - 8;
  90       else if (i < 8)
  91         m <<= 8 - i;
  92     }
  93 
  94   /* low volumes give occasional sour notes */
  95   if (i < 11)
  96     return (11 << 8);
  97 
  98   return ((i << 8) + m);
  99 }
 100 
 101 #endif
/* */
root/drivers/sound/gus_vol.c

DEFINITIONS
