Stocharythm Box §§ Bruitenkor !

Another drum machine for STM32F4 Discovery kit

Electronic free jazz ready !

Funny and strange drum machine controlled by any PC USB AZERTY/QWERTY keyboard plugged into the board. The STM32F4 Discovery kit acts as a USB host for the keyboard.

Work In Progress !!

Features :
9 voices at the moment :

• 6 sample players which can access to 41 famous short samples (800kB)
• 1 sampled kick (no more Synthetic Bass Drum (DaisySP/ Emilie Gillet) because too greedy...)
• 1 white noise with ADSR
• 1 808 snare

Adjustable pan for each instrument.
FX : simple stereo reverb based on Freeverb (in freeverb_stm32.hpp).
Stereo output.

The sequencer is not step based. You define a loop duration and call for sound events which are randomly dispatched in the loop.
These are so-called "stocharythms". You can however quantize their position on a defined grid. You can also do live recording !

Many debug messages through UART (Pin PA2). Please configure your serial port terminal to ISO-8859-15 encoding.

To improve :
[x] noise during UART transmissions
[x] add stereo placement
[ ] make debug messages optional
[ ] remove clicks at the end of some samples
[ ] mute/unmute instruments
[x] delete instrument events in loop
[x] more LED indicators

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Keyboard control :

Single key controls : just hit the key !

• + and - -> final volume (Output DAC)
• ( and ) or arrows up and down -> source volume
• . -> clear loop
• space -> play/pause sequencer
• ! -> play/stop sequencer
• left and and right arrows : slow down or speed up
• * -> start live recording
• / -> stop live recording
• n -> add 2 random events
• b -> delete 2 random events
• T : add 1 event played by instrument 0 / t : play or record instrument 0
• Y : add 1 event played by instrument 1 / y : play or record instrument 1
• U : add 1 event played by instrument 2 / u : play or record instrument 2
• I : add 1 event played by instrument 3 / i : play or record instrument 3
• O : add 1 event played by instrument 4 / o : play or record instrument 4
• P : add 1 event played by instrument 5 / p : play or record instrument 5
• H : add 1 Synthetic Bass Drum event / h : play or record Synthetic Bass Drum
• J : add 1 white noise event / j : play or record white noise
• K : add 1 808 snare event / k : play or record snare
• m : mix up all events in loop
• z : change the 6 samples
• a : randomize velocities of events at the beginning of each loop
• v : randomize velocities of all events
• s : display sequencer status
• d : display list of events in the loop

Multi key commands : press a sequence of keys and submit it with enter
They must all start with letter c, no space, just comma to separate numbers.

• cl : cl<n> : Sets the loop duration at n x 0.1 seconds (ex : cl20 for 2 seconds)
• ca : ca<n> : Creates n random events for each instrument (ex : ca4)
• cr : cr<n>,<instr> : Creates n regular events in the loop for instrument instr (ex : cr1,5 )
• cn : cn<n> : Creates n events (ex : cn10 )
• cq : cq<n> : Quantize events on a n steps loop (original position is lost)

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Developer notes :

I'm using STM32CubeIDE (v1.19).
This is a configurable project with ioc (STM32CubeMX) and BSP files written in C and C++.
It should be easily tailored for other powerful STM32 mcu (cortex M33, M4, M7, M55, ...)

Keyboard configuration :

• Keyboard layout is in azerty_hid_map.h (This one is for AZERTY french keyboards, sorry)
• For mapping single key functions, in file bruitenkor.cpp, modify function : void InterpretKey(uint8_t key, uint8_t keycode)
• You can define new multi key functions in file keyb_command_parser.cpp, don't forget to fill also the table static const Command commandTable[MAX_COMMANDS] = {...}

There are several Git branches :

• Stocharythm : main one
• Simple_demo : minimal synth platform

<<< By Xavier Halgand, Summer 2025 >>>
Thanks : Electrosmith/DaisySP, Emilie Gillet, STM32 team, ChatGPT, ...