Giant Leap

- A step sequencer built on streams.

General concept

Like the header image. There exists a Metronome being a readable stream. It generates objects with a time property consistent with the supplied beats per minute, say 120.

Several transform streams can be applied to extend the message with extra properties, like note information, e.g. a C# with a length of 5 seconds.

Finally the properties are transformed to a message that can streamed to the final write stream MidiOut which wraps the npm module node-midi really and keeps track of messages and if it is time to play them.

So to sum up, messages are basic js objects. The Metronome creates messages and ads a time property. Any following transform streams add on to this object. Finally its written by MidiOut to /dev/midi somehow via node-midi/RtMidi.

When I mention a message I refer to a the plain old js object representing the message.

Warning: Do NOT reuse any instantiated streams like the metronome. Just instantiate another one if you need it. The reason for this is that stream handlers communicate to each other. You don't want to mess with this communication.

Getting started

Dependencies:

Linux/Mac/Windows*
Node 11.9 or higher
node-midi / RtMidi

In the post install script the command ln is used for the creation of a symbolic link to the modules folder. This is a specific linux cmd and will not work on windows. Create a link in the node_modules folder named @giantleap and point it to the modules folder.

$ git clone git@github.com:t638403/giantleap.git
$ cd giantleap
$ npm install

Open myFirstSong.js in an editor.

1. Create a metronome

const Metronome = require('@giantleap/Metronome');
const metronome = new Metronome(120, 4);

2. Create a pattern

const Pattern = require('@giantleap/Pattern');
cont pattern = new Pattern([
	'x...x...x...x...x...x...x...x...',
	'x...x...x.......x...x...x.......',
	'x.x.x.x.x...x...x.x.x.x.x...x...',
	'x...x...x.......x...x...x.......'
]);

2. Create some notes

Add notes in an array, and it will play the round

const Note = require('@giantleap/Note');
const notes = new Note([
	'C3','D3','E3','C3',
	'C3','D3','E3','C3',
	'E3','F3','G3',
	'E3','F3','G3',
	'G3','A3','G3','F3','E3','C3',
	'G3','A3','G3','F3','E3','C3',
	'C3','G2','C3',
	'C3','G2','C3',
]);

3. Find out midi devices

If you have no midi hardware you can still download dozens of virtual devices like synthv1. Once installed run synthv1 and connect it to the output so you can hear it (use Patchage for example). Then run the following js lines.

const MidiOut = require('@giantleap/MidiOut');
MidiOut.displayAvailablePorts();

You'll see something like this.

0: Midi Through 14:0
1: synthv1 129:0

synthv1 has a MIDI in indicator, in the bottem left corner, which flashes when it receives midi input. When it flashes but you do not hear anything you're on the right track at least. Just find out how to connect it to your sound device or turn on the volume.

4. Create an instrument

An instrument adds two keys to the message, device and midi channel.

const midiChannel = 1;
const deviceName = /synthv1 \d+:0/;
const Instrument = require('@giantleap/Instrument');
const synthv1 = new Instrument(deviceName, midiChannel);

Note 1: I use a short reg exp notation to select the device, since numbers seem to change.
Note 2: ALSA makes sensible device names like Jack does not.
Note 3: You can compile node-midi for jack by changing the binding.gyp file in the npm package. You'll find __LINUX_ALSA__ somewhere. Change it to __UNIX_JACK__ or rfm.

5. Stitch together

const MidiMsgr = require('@giantleap/MidiMsgr');
metronome
	.pipe(pattern)
	.pipe(notes)
	.pipe(synthv1)
	.pipe(new MidiMsgr())
	.pipe(new MidiOut())
;