synth.c

   1 /*
   2    Cantaveria - action adventure platform game
   3    Copyright (C) 2009 2010 Evan Rinehart
   4
   5    This program is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU General Public License
   7    as published by the Free Software Foundation; either version 2
   8    of the License, or (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to
  17
  18    The Free Software Foundation, Inc.
  19    51 Franklin Street, Fifth Floor
  20    Boston, MA  02110-1301, USA
  21
  22    evanrinehart@gmail.com
  23 */
  24
  25 #include <synth.h>
  26 #include <seq.h>
  27
  28 /*
  29 timing stuff
  30
  31 ticks -   384 per beat     (tpb)
  32 beats -   120 per minute   (bpm)
  33 samples - 22050 per second (srate)
  34
  35 control happens on tick boundaries
  36 control must take effect on nearest sample boundary
  37
  38 samples per tick = (srate*60) / (bpm*tpb)
  39 which in the above example = 28 and 32760/46080
  40
  41 */
  42
  43
  44 int srate;
  45 int bpm = 120;
  46 int tpb = 384;
  47
  48 int serr = 0; // 1/1000 of a sample
  49
  50 int tick;
  51 int terr = 0; // 1/(bpm*tpb) of a sample
  52 int terrd = 46080; //bpm * tpb
  53
  54 void set_sample_rate(int x){ srate = x; }
  55 void set_bpm(int x){ bpm = x; }
  56
  57
  58 void synth_init(int sample_rate){
  59         srate = sample_rate;
  60         seq_init();
  61 }
  62
  63 void generate(float left[], float right[], int count){
  64         int i;
  65
  66 /* supposed to mix all generators for count samples
  67 this includes synthesizers and sample generators */
  68 /* this loop is unsuitable as an inner loop */
  69         for(i=0; i<count; i++){
  70                 left[i] = 0;
  71                 right[i] = 0;
  72         }
  73
  74
  75 /* instead zero them and pass them to each generator
  76 which will accumulate their output into left and right
  77
  78 in the end divide by maximum number of generators
  79
  80 the final stage is master volume, which will be increased if
  81 the result is too quiet */
  82 }
  83
  84 void control(event* e){
  85 /* we decided on polyphonic synth (and multiple instances of
  86 a playing samlple). important to remember that all controller
  87 events affect entire instrument channels. this means it affects
  88 all generators for that intrument */
  89 }
  90
  91 void synth_generate(float left[], float right[], int samples){
  92         int i=0;
  93         for(;;){
  94                 int next = seq_lookahead(samples);
  95                 if(next < 0) break;
  96                 generate(left+i, right+i, next-i);
  97                 control(seq_get_event());
  98                 i = next;
  99         };
 100         generate(left+i, right+i, samples-i);
 101         seq_advance(samples);
 102 }
 103
 104
 105
 106
 107 /* possible generators (scratch work)
 108
 109 square wave
 110 saw wave
 111 triangle wave
 112 square saw produce a band limited signal
 113
 114 string signal
 115 this uses a karplus strong algorithm
 116 noise -> variable delay (linear interpolating) -> first order low pass
 117
 118 voice signal
 119 formant synthesis
 120 two or three gaussians (perhaps padded) -> IFFT
 121 also works for bell
 122
 123 detuned oscillators
 124
 125 samples on ch 10
 126 just samples
 127
 128 effects
 129 portamento
 130 vibrato
 131 echo
 132 chorus
 133 reverb
 134 appegiator
 135 adsr envelope
 136 */