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