nes-sequencer

This is a attempt to emulate the NES audio hardware using the Web Audio API. The NES traditionally had 4 oscillators:

Two pulse-width oscillators with configurable duty cycles of 12.5%, 25%, and 50%
A triangle wave oscillator (typically used for the bass-line)
A noise channel

Getting the project setup, with examples

After cloning the repo, simply run

npm install
make all

to concatenate files, and open the provided html file in a browser

Docs

Also, make docs will also build the docs and dump them into a docs folder, which you can peek through if you need.

Building songs

Building songs is fairly easy, by passing an object to play. The object will have keys for each oscillator, and arrays for each value. Here's an example

var notes = [
  { frequency: 440, cycles: 30, volume: 0.1 },
  { frequency: 880, cycles: 60, volume: 0.1 },
  { frequency: 440, cycles: 30, volume: 0.1 },
];
var fullMelody = {};
fullMelody[NesSequencer.OSCILLATOR_TYPES.PWM1] = notes;
NES.Sequencer.play(fullMelody);

Note that all time units are provided in integer cycles. The cycles correspond to the NES' APU processor speed, which was 60Hz.

There is also MML support which can make writing songs considerably easier. You can see here in the Kart Kingdom example how you might go about that.

Building the oscillators

The Web Audio API has built-in support for a triangle wave, but the others must be implemented.

For the pulse width oscillator, I was forced to create my own custom PeriodicWave instance after calculating the Fourier series by hand (which came out something similar to series here).

For the noise channel, I created a buffer source and attached a custom buffer and filled it with Math.random() values. I then also attached a BiquadFilterNode to allow me to bandpass-filter frequencies to get "high" and "low" noise.

Basic Pitch Setting etc.

The easiest way to set a pitch is using setPitch:

NES.Oscillator.setPitch('PWM1', 880, 0.1);
NES.Oscillator.setPitch('PWM2', 440, 0.1);
NES.Oscillator.setPitch('TRI' 220, 0.1);
NES.Oscillator.setPitch('NOISE', 100, 0.1);

You can change the pulse width as well

NES.Oscillator.setPulseWidth('PWM1', 0.25);

Listening for events

The sequencer also emits a handful of events you can use to react to internal changes

NES.Events.Bus.addEventListener(NES.Events.Types.OSCILLATOR_CHANGE, function(e) {
  console.log(e.oscillatorIndex, e.frequency, e.volume);
});

NES.Events.Bus.addEventListener(NES.Events.Types.SEQUENCER_TICK, function(e) {
  console.log('The sequencer ticked (this happens A LOT)', e.currentCycle);
});