play(note, velocity, secondsFromNow, susTime) {
    this.triggerAttack(note, velocity, ~~secondsFromNow);
    this.triggerRelease(~~secondsFromNow + (susTime || DEFAULT_SUSTAIN));
  }
Play tells the MonoSynth to start playing a note. This method schedules
 the calling of .triggerAttack and .triggerRelease.

 @method play
 @for p5.MonoSynth
 @param {String | Number} note the note you want to play, specified as a
                                frequency in Hertz (Number) or as a midi
                                value in Note/Octave format ("C4", "Eb3"...etc")
                                See <a href = "https://github.com/Tonejs/Tone.js/wiki/Instruments">
                                Tone</a>. Defaults to 440 hz.
 @param  {Number} [velocity] velocity of the note to play (ranging from 0 to 1)
 @param  {Number} [secondsFromNow]  time from now (in seconds) at which to play
 @param  {Number} [sustainTime] time to sustain before releasing the envelope. Defaults to 0.15 seconds.
 @example
 <div><code>
 let monoSynth;

 function setup() {
   let cnv = createCanvas(100, 100);
   cnv.mousePressed(playSynth);
   background(220);
   textAlign(CENTER);
   text('tap to play', width/2, height/2);

   monoSynth = new p5.MonoSynth();
 }

 function playSynth() {
   userStartAudio();

   let note = random(['Fb4', 'G4']);
   // note velocity (volume, from 0 to 1)
   let velocity = random();
   // time from now (in seconds)
   let time = 0;
   // note duration (in seconds)
   let dur = 1/6;

   monoSynth.play(note, velocity, time, dur);
 }
 </code></div>