Chord

What is Chord?

Chord is a monophonic synth program for the original Nintendo Gameboy. The idea was to make something that can be played like an instrument, but with the limitations of the few buttons available. Now with MIDI support through ArduinoBoy.

You build "chords" of five notes and play them back using the pulse wave channel, with full sound register settings control and optional arpeggiator.

How do I get it on my gameboy?

Chord is best enjoyed on a real gameboy. Get the official cart over at HobbyChop, an etsy store focusing on Arduinoboy and custom carts. It looks gorgeous!

Another option is a programmable cartridges, which there are several out there. I did all development using an EMS USB 64M Smart Card. I also like Analogue Pocket, which can run openFPGA off a SD card. Both Android and iOS now have gameboy emulators too, with Delta arriving early 2024 on the App Store.

Get Arduinoboy at HobbyChop, adding MIDI support, allowing you to play notes, change parameters and sync the playback clock.

Videos

Guide

Play Mode

#tip: D-pad is sticky, meaning that if the right button is pressed it will only be released once all d-pad buttons are released.

Editing

1. Channel mode:

• Monophonic or 3 channel polyphonic.

2. Left button mode:

• Shift octave up 1 / move current chord back to start

3. Save/load:

• 8 slots avalable for saving (press A to save/load)

4. Arpeggio:

• External clock sync.
• Timer: An overflow timer incremented at 4096 Hz.
• Arpeggio mode: none, random, up and down.
• Number of octaves.

5. Pitch sweep:

• Sweep Time.
• Frequency increase/decrease.
• Nr of sweeps.

6. Sound:

• Wave duty: (12.5%, 25%, 50% or 75%).
• Sound length.

7. Envelope:

• Initial envelope value.
• Envelope direction (up,down).
• Number of envelope sweeps.

8. Selected control:

• Navigate with d-pad. Change values with a and b.

#tip 1: Some conrols allow notes to be played with a, b, start and select. For example to test arpeggios.

#tip 2: When editing notes d-pad up and down can still be used to shift the current chord up and down.

Polyphonic Mode

Polyphonic mode works slighlty different to monophonic mode. All notes are sustained during button presses and less settings are available, in order to match the sound across all three channels. The channels available are divided into groups to prevent root notes of a chord being discarded, by new key presses.

Arduinoboy

I recommend getting your Arduinoboy from HobbyChop. Chord can be used with MIDI mode 5, but may or may not support MIDI clock (0xf8) depending on what version and/or fork you are using.

MIDI Note On/Off

When a new MIDI note is received it will populate the first available silent slot and start playing. Receiving a note off will silence the note but the slot will stay populated until a new note comes and takes its place.

MIDI CC

Parameters are controlled by the MIDI CC values for CC1 - CC14. MIDI CC64 will shift the parameter groups around by one step to allow keyboards with a limited number of knobs to control more parameters.

Groups: Envelope, Sound, Pitch Sweep, Arpeggio, Tempo

MIDI Clock

MIDI clock sends 24 ticks per beat. Use overflow timer to control the speed of playback. For example 24 will playback at the control device's bpm, 12 will play at double speed and 6 at 4x.