Sonic Piで、自作Synthをつくる ref: http://qiita.com/yoppa/items/829d25addf499824d2f9

file0.txt

use_synth :fm
play 60
sleep 0.5

file1.txt

Sonic Pi.app/etc/synthdefs/designs/sonic_pi/synths

file2.c

SynthDef("piTest", {
    //出力先のバスを引数で設定
    arg out_bus = 0;
    //440HzのSin波生成
    var mix = SinOsc.ar(440).dup;
    //Envelope生成
    var env = EnvGen.ar(Env.perc(0.0, 1.0, 1.0), doneAction: 2);
    //Envelope適用
    mix = mix * env;
    Out.ar(out_bus, mix);
}
//ファイルの出力先を指定
).writeDefFile("/Users/tado/Desktop/my-synths");

file3.txt

#Synth定義を読み込む(フォルダの場所を指定)
load_synthdefs "/Users/tado/Desktop/my-synths"
#Synth名を指定
use_synth :piTest

play 60
sleep 1.0

file4.c

SynthDef("piTest", {
  //音程と音量を引数を指定
  arg note = 52, amp = 1, out_bus = 0;
  //音程(MIDI番号)から周波数へ
  var freq = note.midicps;
  //周波数をSin波に適用
  var mix = SinOsc.ar(freq).dup;
  var env = EnvGen.ar(Env.perc(0.0, 1.0, 1.0), doneAction: 2);
  mix = mix * env;
  Out.ar(out_bus, mix);
}
).writeDefFile("/Users/tado/Desktop/my-synths");

file5.txt

load_synthdefs "/Users/tado/Desktop/my-synths"
use_synth :piTest

loop do
  play rrand_i(40, 80), amp: rrand(0.5, 0.8)
  sleep 0.5
end

file6.c

SynthDef("piTest", {
    arg out_bus = 0, note = 52, amp = 1, attack = 0, release = 1, pan=0;
    var freq = note.midicps;
    var mix = SinOsc.ar(freq);
    var env = EnvGen.ar(Env.perc(attack, release, 1.0), doneAction: 2);
    //Panを適用
    mix = Pan2.ar(mix * env, pan);
    Out.ar(out_bus, mix);
}
).writeDefFile("/Users/tado/Desktop/my-synths");

file7.txt

load_synthdefs "/Users/tado/Desktop/my-synths"
use_synth :piTest

loop do
  play rrand_i(40, 80), amp: rrand(0.5, 0.8), pan: rrand(-0.8, 0.8), release: 2.0
  sleep 0.5
end

file8.c

SynthDef("piTest", {
    arg out_bus = 0, note = 52, amp = 1, attack = 0, release = 1, detune = 1.01, pan=0;
    var freq = note.midicps;
    var mix =  MoogFF.ar(
        Pulse.ar([freq,freq*0.5], 0.8),
        freq*2.5,
        128
    );
    var env = EnvGen.ar(Env.perc(attack, release, amp), doneAction: 2);
    mix = Pan2.ar(mix * env, pan);
    Out.ar(out_bus, mix);
}
).writeDefFile("/Users/tado/Desktop/my-synths");

file9.txt

load_synthdefs "/Users/tado/Desktop/my-synths"
use_synth :piTest

live_loop :live do
  with_fx :flanger do
    use_random_seed 8
    32.times do
      3.times do
        ns = (scale :c1, :mixolydian, num_octaves: 8)
        play ns.choose, attack: 0.0, release: 2.0, amp: 1.5
      end
      sleep 0.25
    end
  end
end