global {
  srate 48000;   // DAT-quality 
  krate  2400;   // 417 us
}

//
// instr vtone
// shaped sinewave 
//

instr vtone (num) {

  // declarations
 
  // envelope settings
  ivar atime;   // attack
  ivar rtime;   // release

  // internal env state 
  ivar attack;  
  ivar release;
  ivar sustain;

  ivar a;       // sets osc f
  
  ksig env;     // env output

  asig x, y;    // osc state
  asig init;


  // **********************
  // computed during i-pass
  // **********************

  // turns MIDI number into 
  // oscillator constant 

  a = 2*sin(3.1415927*
	    cpsmidi(num)/s_rate);

  // envelope computation

  atime = 0.3; // attack time (s)
  rtime = 0.2; // decay time (s)

  // computes envelope state

  if (dur > atime + rtime)
    {
      attack = atime;
      release = rtime;
      sustain = dur - atime
	- rtime;
    }
  else
    {
      attack = dur/2;
      release = dur/2;
      sustain = 0;
    }

  // **********************
  // computed during k-pass
  // **********************

  env = kline(0, attack, 1, sustain,
	      1, release, 0); 

  // **********************
  // computed during a-pass
  // **********************

  if (init == 0)
    {
      x = 0.25;
      init = 1;
    }

  x = x - a*y;
  y = y + a*x;
  
  output(y*env);

}