DOOM OS: a custom firmware for the Roland SP-404MK2

DOOM OS

DOOM OS is a heavily modified version of the original 5.52 firmware. It adds a graphical pattern sequencer, a mixer, instruments, an arpeggiator, parameter locking, effect automation, custom shortcuts and much, much more.

Current version: 0.7.3 build 733D (2026-11-04)

Quick installation: Use the web patcher to install DOOM OS

Features

DOOM OS includes many more features and improvements than can be listed here. Check out the full manual for a complete overview.

Pattern sequencer with a graphical interface: see and edit your pattern as a grid while it plays
Piano roll
Live recording with a rehearse mode, quantize, swing, fixed velocity and note length
Eight pattern tools: quantize, swing, shift, double, halve, reverse, humanise, transpose
Track and pattern settings: mute, solo, volume, swap pad, paste, clear, tempo, pattern length
Mixer with a live level meter for every track
Easy visual side chaining
Live waveform view
20 Built-in instruments and 11 drum kits
Parameter locking of every instrument's parameters
An arpeggiator
Effect automation: record your effect knob moves and edit them step by step
3-band parametric EQ for up to 16 tracks
Pad mute and solo mode
Zoomed view of four tracks
Undo and redo up to 12 steps
Help mode: press any button to show what it does
Custom shortcuts (key combos)
A DOOM OS tab in the system settings
Six boot animations
And much, much more!

Improvements

Safer pattern saving: patterns are first written to a new file, and the original is only removed once the new file has been written successfully
Everything from the original firmware remains available. DOOM OS doesn't remove or replace any stock functionality. Simply exit DOOM OS to return to the original interface.

How to install

The easiest way to install DOOM OS is by using the web patcher:

https://klangfeldlabs.com/doom-os/patcher

You can also download this repository as a ZIP file (under the Code button), unzip it and open index.html in your browser. Just follow the instructions on the page.

Manual installation

Download the 5.52 system update from Roland's support page and unzip it.
Open the patcher and load SP404MKII_APP1.bin. Everything happens in your browser, nothing is uploaded. The patcher only accepts the official 5.52 file and checks the result against checksums.txt.
Download the patched SP404MKII_APP1.bin and copy it to the root of an SD card formatted as FAT32. The updater does not support exFAT.
Insert the card, hold SHIFT while you turn the SP on, and press the VALUE knob when the update menu appears.
When the update is done, turn the SP off and on again.

To go back to the original firmware, just run the updater with the original Roland firmware.

Main controls

It's recommended to read the full manual as there are too many new features and shortcuts to list here.

The basics:

Control	What it does
REMAIN + SUB PAD	Open DOOM OS! (works from any screen)
EXIT	Close DOOM OS and save your changes
Hold SHIFT for 3 seconds	Help mode: press any control to see what it does
PATTERN SELECT	Start / stop
Pads 1-16	Turn steps on or off in the selected row
Turn VALUE	Select a row
Hold SUB PAD + tap pads	Choose the sample for a new row
Hold a step + CTRL 1 / 2 / 3	Velocity / length / timing of that step
Hold a step + SHIFT + CTRL 1	Pitch of that step
Press VALUE	Open the piano roll
HOLD	Play the pads instead of editing steps
REC	Press once to rehearse, again to record
PATTERN EDIT	Pattern tools
RECORD SETTING	Show track panel or pattern panel
Hold RECORD SETTING	Open the mixer
START/END	Open the instrument editor on an instrument track
SHIFT + START/END	Show live waveform view
SHIFT + PATTERN SELECT	Undo
REMAIN + PATTERN SELECT	Redo

The full guide and every control are in the manual.

Coming next

This is not a roadmap, but upcoming features include a song mode, clip launcher, advanced sample editing and chopping, and a modular system to load in custom modifications.

Status

DOOM OS is still in the early stages of development, so expect some rough edges.

Found a bug? Open an issue and include the version shown on the VERSION tab in Utility > System.

You can also drop feature requests at the DOOM OS subreddit at reddit.com/DOOMOS.

Changes are listed in CHANGELOG.md.

Disclaimer

This is an unofficial project, not affiliated with or endorsed by Roland. Modifying your firmware is at your own risk and may void your warranty. DOOM OS is named in tribute to MF DOOM. Made by Klangfeld Labs. Free to use, commercial music included; copying, changing or passing it on needs permission (LICENSE).