Keypad synth revA

SPEAK//HARD

A handheld speech beat machine on an ESP32-S3. Four instruments (SAM voice, Talkie LPC voice, bytebeat, a 12-piece drum kit) on a 16-step sequencer, seven voice FX plus stutter/reverse/tape-stop/scratch, and a live HUD on a 128x128 OLED.

Co-created by Mark Hellar and Claude (Anthropic AI): hardware, design and sound direction by Mark; firmware and PCB layout co-written with Claude. PCB milled and soldered by Mark Hellar.

Hardware

Pins

PCB

Single-sided, all copper on B.Cu, designed for CNC isolation milling on a 100 x 70 mm copper-clad blank. Modules plug into female headers; the keypad and pot modules lie on SMD edge pads with their right-angle pins.

• hardware/ KiCad 10 project (schematic, PCB, symbol library, ks_cnc.pretty footprints)
• hardware/cnc/ Gerbers (B.Cu, Edge.Cuts), PTH/NPTH drills, a 1:1 fit-test PDF, and ready-made GRBL G-code: 1_isolation_0.1vbit.nc (0.1 mm 20 deg V-bit, Z -0.05) -> 2_holes_1.0drill.nc -> 3_mounting_2.0drill.nc -> 4_outline_score_0.1vbit.nc. load_and_mirror.tcl regenerates the G-code in FlatCAM (mirrored, since the copper is on the bottom); fix_drill_spinup.py patches drill files for GRBL laser mode. See CNC_CHEATSHEET.txt.

Print PRINT_1to1_fit_test.pdf and check your modules against it before milling: the OLED, keypad and pot outlines were measured from photos and typical specs.

Firmware

firmware/speakbeat_hard/ is the instrument. firmware/keypad_bringup/ is a quick test (keys play notes, OLED grid).

Build with the Arduino IDE or arduino-cli:

• ESP32 Arduino core 3.x (tested on 3.3.5)
• Board: ESP32S3 Dev Module, USB CDC On Boot: Enabled, PSRAM: enabled
• Library: U8g2. esp-dsp ships with the ESP32 core.

arduino-cli compile --fqbn "esp32:esp32:esp32s3:CDCOnBoot=cdc,PSRAM=enabled" firmware/speakbeat_hard
arduino-cli upload  --fqbn "esp32:esp32:esp32s3:CDCOnBoot=cdc,PSRAM=enabled" -p <port> firmware/speakbeat_hard

If the board sits silent after an upload, press RST: on the SuperMini the auto-reset can leave it in the bootloader.

Audio runs at 22.05 kHz in a task on core 0 (it also scans the keypad); the display loop runs on core 1.

Controls

The left keypad column holds the modifiers; the other 12 keys are pads.

[MODE ] [ pad 0 ] [ pad 1 ] [ pad 2 ]
[FX   ] [ pad 3 ] [ pad 4 ] [ pad 5 ]
[SEQ  ] [ pad 6 ] [ pad 7 ] [ pad 8 ]
[SHIFT] [ pad 9 ] [ pad 10] [ pad 11]

Tap a modifier for its quick action. Hold it and the screen shows what the 12 pads do while it's held.

With REC on, everything you play is quantized into the 16 steps. It boots stopped with an empty pattern.

Sound engine

• SAM words are pre-rendered into PSRAM, so they can be scratched, stuttered and granulated.
• Talkie words are decoded to LPC frames at boot and resynthesized live through the 10-pole lattice filter, so pitch, formant, voicing and coefficients can be bent while it talks.
• VOX is a 16-band vocoder (esp-dsp biquads) with SAM as the modulator and a driven polyBLEP chord carrier. Chord sets: DROP, DREAD, EPIC, MACHINE.
• Drums are synthesized: driven sine kick with a click, metal snare, multi-burst clap, 808-style hats from six detuned square waves, FM clangs, and CHUG, a fuzz power chord that follows the chord progression.
• Kick, 808 and SLAM duck the voices; a soft compressor and a 40 Hz highpass sit on the master.
• tools/drumsim.py is a Python port of the drum engine that prints each hit's level; run it after changing the PERC[] table.

Credits

• SAM (Software Automatic Mouth, Don't Ask Software, 1982). C port by Sebastian Macke; ESP8266SAM by Earle Philhower.
• Talkie by Peter Knight; vocabularies converted by Armin Joachimsmeyer. LPC tables and lattice filter via ESP8266Audio's AudioGeneratorTalkie.
• esp-dsp by Espressif.
• U8g2 by olikraus.
• Bytebeat formulas from the viznut (2011) bytebeat scene.

Details in THIRD_PARTY.md.

License

GPL v3. See LICENSE.