Set up basic sequencer API

src/modules/Sequencer.js

@@ -0,0 +1,51 @@
+import notesToFrequencies from 'notes-to-frequencies';
+
+/**
+ * A 64-step sequencer with grid and recording modes
+ */
+export default class Sequencer {
+  constructor(length) {
+    this._sequence = new Array(length);
+    this._tempo = 120;
+    this._currentIndex = 0;
+  }
+
+  setTempo(bpm) {
+    this._tempo = bpm
+  }
+
+  getMillisecondsPerStep() {
+    return (60000 / this._tempo) / 4;
+  }
+
+  setNoteAtIndex(index, note) {
+    this._sequence[index] = note;
+  }
+
+  trigger(callbacks) {
+    this._onTriggerCallbacks = callbacks;
+  }
+
+  play() {
+    const index = this._currentIndex;
+    const note = this._sequence[index];
+    const frequency = notesToFrequencies(note);
+
+    if (note) {
+      this._onTriggerCallbacks.forEach(cb => cb(frequency));
+    }
+
+    setTimeout(::this.play, this.getMillisecondsPerStep());
+
+    if (index === this._sequence.length - 1) {
+      this._currentIndex = 0;
+    }
+    else {
+      this._currentIndex++;
+    }
+  }
+
+  clear() {
+    this._sequence = new Array(16);
+  }
+}

src/stock-synths/ThreeOscSynth.js

@@ -13,6 +13,7 @@ import FrequencyAnalyzer from '../modules/FrequencyAnalyzer.js';
 import Ringmod from '../modules/Ringmod.js';
 import Chorus from '../modules/Chorus.js';
 import Panner from '../modules/Panner.js';
+import Sequencer from '../modules/Sequencer.js';
 
 export default class ThreeOscSynth {
   constructor() {
@@ -31,8 +32,9 @@ export default class ThreeOscSynth {
     this.ringmod = new Ringmod();
     this.chorus = new Chorus();
     this.panner = new Panner();
+    this.sequencer = new Sequencer(16);
 
-    const { synth, midi, oscGroup, filter, mixer, vca, envelope, lfo, delay, eq3, computerKeyboard, frequencyAnalyzer, ringmod, chorus, panner } = this;
+    const { synth, midi, oscGroup, filter, mixer, vca, envelope, lfo, delay, eq3, computerKeyboard, frequencyAnalyzer, ringmod, chorus, panner, sequencer } = this;
     const { osc1, osc2, osc3 } = oscGroup;
 
     synth.addModule(oscGroup);
@@ -69,6 +71,21 @@ export default class ThreeOscSynth {
       envelope::envelope.triggerRelease
     ]);
 
+    envelope.setAttack(0);
+    envelope.setSustain(1);
+    envelope.setDecay(0.2);
+    envelope.setRelease(0.2);
+
+    sequencer.trigger([
+      osc1::osc1.setFrequency,
+      envelope::envelope.triggerADS
+    ]);
+
+    sequencer.setNoteAtIndex(0, 'C4');
+    sequencer.setNoteAtIndex(4, 'C#4');
+    sequencer.setNoteAtIndex(8, 'D4');
+    sequencer.setNoteAtIndex(12, 'C#4');
+
     midi.trigger(osc1::osc1.setFrequency);
   }
 }