triggerAttack(note, velocity, secondsFromNow = 0) {
    var freq = noteToFreq(note);
    var vel = velocity || 0.1;
    this.oscillator.freq(freq, 0, secondsFromNow);
    this.env.ramp(this.output.gain, secondsFromNow, vel);
  }
Trigger the Attack, and Decay portion of the Envelope.
 Similar to holding down a key on a piano, but it will
 hold the sustain level until you let go.

 @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
 @method  triggerAttack
 @for p5.MonoSynth
 @example
 <div><code>
 let monoSynth;

 function setup() {
   let cnv = createCanvas(100, 100);
   cnv.mousePressed(triggerAttack);
   background(220);
   text('tap here for attack, let go to release', 5, 20, width - 20);
   monoSynth = new p5.MonoSynth();
 }

 function triggerAttack() {
   userStartAudio();

   monoSynth.triggerAttack("E3");
 }

 function mouseReleased() {
   monoSynth.triggerRelease();
 }
 </code></div>