README

STEPPER is a 16-step sequencer for the Game Boy Advance (GBA).

It features an intuitive workflow inspired by Elektron instruments with per-trigger parametrization that allows access to the 4 DMG sound channels in the console (2 square waves channels, 1 custom wave channel and 1 noise channel). Supports 4 banks of 8 patterns that can be queued for live performance.

Controls

• D-Pad: Moves the cursor.
• Start: Start/Stop the sequence.
• Select: Context dependent mod key. Used for:
  • Quick saving the current bank.
  • Copy pasting.
  • Adjusting notes by octaves.
  • Adjusting bpm by multiples of 10.
• B: Toggles channels/triggers and play/pause/stop, switches banks and patterns.
• A: Hold it to adjust trigger parameters.
• L/R: Change trigger notes, parameter values, or BPM.

Save/Load

STEPPER supports up to 4 banks of 8 patterns each. The current bank is saved by switching banks or selecting the current one in the bank section. The banks are saved to the SRAM and upon launching STEPPER the last saved state will be loaded. Use "Select + Start" to quick save the current bank.

Patterns

Patterns can be changed or edited by navigating to the left column with the cursor. Pressing the B button will queue a pattern to run on the next cycle. The queued pattern will be highlighted in blue. Only on pattern can be chained at the moment.

We can edit different patterns other than the one that is currently playing. The pattern we are currently editing is represented by a grey/blue cursor whilst the one in play is highlighted in white.

Each pattern stores information about active channels and their trigger notes and parameters. BPM can also be stored independently for each pattern.

Note selection

Notes can be changed by pressing "L" or "R" over an active trigger. If the cursor is on the channel selection mode, "L" and "R" will transpose all trigger notes instead. Holding "Select" while adjusting notes will make it jump by an octave instead of a semitone.

Parameters

Channels 1 and 2 allow us to control the square wave duty cycle and envelope (Initial volume, direction and time). Additionally, channel 1 can access the "sweep" parameters, which when the time is not zero allows for some interesting FX.

Channel 3 is the wave channel. In this channel we have access to 2 programmable waves that can be edited manually or selected with 4 available presets (sine, saw, square, random). The waves can be played independently (mode A or B) or one after another (Mode A + B). This channel has no volume envelope thus a note will keep playing until it encounters an active trigger with zero volume or a different pitch.

Channel 4 is the noise channel, mostly used for percussive effects. It uses an envelope to shape the sound and has two modes of operation. Mode A is more rounder and mode B sounds more metallic.

Adjust the parameters by holding "A" hovering over a trig. Parameters are stored per trigger and adjusted individually for each of them. If the cursor is on channel selection mode, when adjusting the channel parameters these will be copied to all 16 triggers. Note that this global adjustment is not stored when saving banks and patterns. The grey color on the global adjustment helps differentiate between trigs and channel parameters. A compatible trig/parameter can be pasted into a channel to apply it to all triggers.

Copy/Paste

The GBA has a limited set of controls but using STEPPER's contextual clipboard we can greatly speedup the editing workflow. We can use "Select + B" (Copy) or "Select + A" (Paste) to perform clipboard operations.

If the cursor is selecting a pattern, the entire pattern will be copied, including active channels, triggers and parameters. Patterns can only be pasted in other patterns.

Channels can be copied to other patterns or channels. If the paste destination is a channel other than the original one, only the notes and active triggers will be copied. If the channel is of the same type, all the parameters will also carry over.

Copying a trigger transfer its pitch (note), active state (on/off) and its parameter settings (Assuming the target is compatible, as explained above). If we only want to copy the parameters, hold "A" to enter parameter select mode and press "Select" to copy them. Now you can paste them to any compatible trigger.

Note that the clipboard doesn't currently transfer between banks due to the platform's limitations.

Using other gear and synchronization

Currently STEPPER has no MIDI sync but I've began research on implementing CV gate out using the GBA's link cable. No ETA for this, since I'm missing a few things to test my theories in hardware, but I'll keep you all posted. In the future something like ArduinoBoy could be implemented to provide this functionality, but in the meantime STEPPER can work with other gear by manually timing the playing head using a click/metronome or sampling patterns from STEPPER to later arrange it into a full song in your DAW or sampler of choice. The latter is my preferred approach.

Keep in mind that the BPM reported by STEPPER can be a bit off since it uses whole integer values for timing adjustments, meaning that you may need to set up your DAW/sampler to a fractional BPM value or use time stretching to get the loops perfectly in time (For example 107 BPM in STEPPER and 107.6 on your DAW).