Death's Hand

Listen to it → Fourteen renders from the same DSP the module runs.

An evil West-Coast style complex oscillator for the Electrosmith patch.Init and VCV Rack — two oscillators where the modulator shapes the primary through through-zero FM, a wavefolder (timbre + symmetry), and AM / ring mod — plus three ways to make it misbehave: self-feedback, chaos (the primary FMs the modulator back) and a Lorenz-attractor modulator, and a unison stack of up to four drifting voices and a sub. Three character macros play all of it from the front panel: FLESH, MALICE and LEGION. One portable DSP core, three targets:

dsp/      portable engine — no heap, no platform headers, volts in / volts out
hw/       Electrosmith patch.Init() firmware (libDaisy)
vcv/      VCV Rack 2 plugin
test/     host tests, WAV renders, aliasing analysis

     ┌──────── chaos: primary FMs the modulator back ◄─────┐
     ▼                                                      │
modulator ──┬───────────────────────────────────────► MOD OUT
(sine/tri/  │ linear through-zero FM                        │
 saw/sq/    ├──► primary (sine core) ◄── self-feedback PM ──┤
 Lorenz)    │        │ ─────────────────────────────────────┘
            ├──► timbre mod ─► wavefolder (timbre, symmetry; exact DC removal)
            │                    │
            └──► AM / ring ─────►× ─► 4× decimator ─► OUT

Everything runs 4× oversampled and is decimated with a 129-tap Kaiser FIR.

Reading the panel

There are no words on the panel, only sigils. The top row is the voice: pitch and the three character macros. Below them are the settings the patch.Init keeps on its shift layer. Each sigil repeats on the jack that modulates it, so the panel reads in columns.

Sigil	Means
Eye (lashes)	Pitch · V/OCT input
Zigzag in a circle	FLESH macro · its CV
Eight-arrow star	MALICE macro · its CV
Four rings	LEGION macro · its CV
Vesica (two rings)	Ratio, or modulator pitch when free
Triangle in a circle	Modulator shape. The red last stop is Lorenz
Hourglass	Symmetry trim · its CV
Slit eye	Fine tune
Key	Ratio lock. The red arrow is up = locked
Crossed ring ⊗	Routing: FM, + timbre mod, + AM, + ring · its trigger input
Spiral	External FM input
Pillars and lightning	Sync input
Blood drop (solid)	Primary out
Blood drop with rings	Modulator out

Bone rings mark inputs, red rings mark outputs, and the outputs sit on the altar. The hand, the edge runes and the summoning circle are decoration.

The macros

Each macro sweeps several parameters at once, each over its own stretch of the knob, so one knob (or one CV) tells one story. +/-5 V at a macro's jack sweeps its whole range, so an envelope into FLESH opens the whole voice.

Macro	Sweeps	Along the knob
FLESH	FM index, wavefold, symmetry, modulator → timbre	FM sidebands first, then the fold opens (glassy, then snarling), then asymmetry and a moving fold
MALICE	self-feedback, chaos, extra FM	The lower half is feedback only: sine to saw, still harmonic. The edge into chaos runs from about 0.55 to 0.8. The top is possessed
LEGION	sub, voices, spread, drift	The sub arrives first, then detuned voices fade in one by one, then they drift apart

The host tests hold each macro to its story: FLESH's brightness climbs at every step (220 Hz → 6.8 kHz centroid), MALICE stays harmonic to halfway and is fully inharmonic by 0.9, and LEGION's beating grows from 2.8× to 4.8×. The curves live in dsp/Macros.hpp.

Measured (host tests)

1V/oct tracking, −3 V … +5 V	worst error 0.09 cents
Alias energy, heavy fold @ 2.96 kHz	−9 dB → −84 dB with 4×
Alias energy, FM index 1.0 @ C7	−40 dB → −84 dB with 4×
Self-feedback 0 → 0.5 → 1	pure sine (H2 −117 dB) → saw-like (H2 −10 dB) → noisy
60 s worst-case evil (fb, chaos, Lorenz, all max)	finite, alive, no DC lock-up, at 4 pitches
Output range	±5 V nominal, DC-free; heavy feedback/chaos peaks are soft-capped at 7.2 V
FLESH 0 → 1: spectral centroid	220 Hz → 6.8 kHz, rising at every step
MALICE: inharmonic share at 0.5 / 0.8 / 0.9	0.00 / 0.97 / 1.00
LEGION 0.4 → 1: beating	2.8× → 4.8×
Unison: 4 voices, no spread vs 1 voice	identical to within 0.05 mV
Unison: 4 voices spread, biased fold	beat-rate wobble 0.05 V (0.26 V without the envelope-aware DC fix)
patch.Init flash / RAM	106 KB of 128 KB / 36 KB (arm-gcc 13.3)

Flash your patch.Init

Fastest: prebuilt binary

1. Download deaths-hand.bin from the latest release. Every asset is signed; see Verifying releases.
2. Put the Patch SM into its bootloader: hold BOOT, tap RESET, release BOOT (both buttons are on the Patch SM board on the back of the module).
3. Open Electrosmith's Daisy Web Programmer in Chrome (it uses WebUSB), connect the module over USB, choose deaths-hand.bin and flash.

From source (macOS)

brew install --cask gcc-arm-embedded
brew install dfu-util
git submodule update --init --recursive     # pulls lib/libDaisy
make -C lib/libDaisy                        # once
make -C hw                                  # → hw/build/deaths-hand.bin
make -C hw program-dfu                      # after BOOT + RESET

make -C hw CPU_METER=1 builds a variant that prints DSP load once a second over USB serial (screen /dev/tty.usbmodem* 115200). That's the number to watch as the engine grows.

patch.Init control map

Each knob has two jobs. Hold the button to reach the shift layer. A parameter only moves once its knob passes through the stored value (soft takeover), so switching layers never makes the sound jump.

Knob	Front	Hold button (shift)
1 (CV_1) + jack CV_5	Pitch, 6 octaves around C4. Jack is 1V/oct	Ratio, 11 steps (0.25, 0.5, 1, 1.5, 2, 3 … 8). With the toggle down: free modulator pitch, ~1 Hz LFO up to C7
2 (CV_2) + jack CV_6	FLESH	Modulator shape: sine, triangle, saw, square, Lorenz (5 zones)
3 (CV_3) + jack CV_7	MALICE	Symmetry trim (noon = none), added to FLESH's
4 (CV_4) + jack CV_8	LEGION	Fine tune, ±1 semitone (noon = in tune)

Jacks always drive the front-panel parameter: ±5 V sweeps a macro's whole range.

Other	Does
Button tap	Next routing: FM → FM + timbre mod → FM + AM → FM + ring (LED gets brighter each step)
Toggle	Up = ratio-locked modulator, down = free
Audio IN L	External FM, audio rate, summed with the modulator
Audio IN R	Symmetry CV (±5 V), added to the trim
Gate 1 / Gate 2	Hard sync / next routing
Audio OUT L / R	Primary / modulator
CV OUT 1	Modulator as 0–5 V CV (an LFO in free mode, a chaotic one with Lorenz)
CV OUT 2 / LED	Routing brightness; full while shift is held

Six evil patches

Rendered in test/out/ex*.wav by the same engine and the same panel mapping the firmware runs. Knob positions are clock faces: 7:00 is fully counter-clockwise, 12:00 is centre, 5:00 is fully clockwise. "S1"–"S4" means hold the button and turn knob 1–4. Routing is the number of taps after power-on. Untouched shift knobs stay at their defaults: ratio 1:1, sine, symmetry and fine at noon.

1 · Reactor hum. A low drone whose feedback breathes in and out. Toggle up, routing 0. Pitch 8:40, FLESH 10:30, LEGION 8:10, S1 8:20 (ratio ½), S3 1:30. Rock MALICE slowly between 8:00 and 12:00.

2 · Lorenz growl. A chaotic modulator in audio range, like an engine that won't idle. Toggle down, routing 1. Pitch 9:30, S1 1:10, S2 4:00 (Lorenz). Ease FLESH from 11:00 to 1:00.

3 · Chaos bells. Inharmonic struck metal that gets more unhinged as it goes. Toggle up, routing 2. Pitch 12:00, FLESH 7:30, S1 12:00 (ratio 3). Sequencer into CV_5, a fast decaying envelope (0–2.5 V) into CV_6 (FLESH), trigger both together. Turn MALICE from 11:30 to 3:30.

4 · Feedback scream. The pitch dives while feedback tears into noise. Toggle up, routing 0. FLESH 1:00, S1 10:10 (ratio 1.5), S3 10:00. Together, sweep pitch from 4:10 to 9:30 and MALICE from 12:00 to 5:00.

5 · Possession. Everything rising, then the modulator turns chaotic. Toggle up, routing 3. Pitch 10:20, LEGION 10:00, S1 11:05 (ratio 2), S2 2:00 (square), S3 2:30. Sweep FLESH from 11:30 to 4:00 and MALICE from 9:30 to 3:30, then flip S2 to 4:00 (Lorenz) halfway.

6 · Legion. One voice becomes a swarm while the fold opens. Toggle up, routing 0. Pitch 8:40, MALICE 9:00. Sweep LEGION from 8:30 to 5:00 and FLESH from 10:00 to 1:00.

Things to verify on your unit (top of hw/main.cpp)

• kAudioFullScaleV: the volts a full-scale codec sample produces. It's set conservatively, so if the output is quiet, measure it and lower the number.
• kInvertAudio: the Patch SM's audio stages invert polarity. It doesn't matter for tones, but it does for a ramp used as CV.
• kPitchCvScale / kPitchCvOffset: 1V/oct trim. Send exactly 1 V and 3 V into CV_5 and use libDaisy's VoctCalibration to get the two numbers.
• Toggle direction: if "up" turns out to be free mode, flip ps.ratioLock.

Host tests

make -C test analyze    # tests + renders + spectrograms (needs numpy/scipy/matplotlib)

Writes test/out/*.wav (including demo.wav, the six ex*.wav patches and the feedback/chaos sweeps) and test/out/aliasing.png. The suite checks pitch accuracy, stability under abusive parameters and external FM, through-zero behaviour, the feedback spectrum, that chaos actually breaks periodicity, Lorenz boundedness from 0.01 Hz to 20 kHz, 60-second worst-case runs, the shift-layer pickup logic, and output bounds.

VCV Rack

The plugin mirrors the patch.Init: the same four front knobs, the shift-layer settings as their own knobs, a routing knob with a trigger input, and the same jacks. Knobs and CVs go through the same cosc::panelToParams as the firmware, so a patch translates one-to-one.

Each release has signed packages for Linux x64, Windows x64, macOS x64 and macOS arm64. To build one yourself:

scripts/fetch-rack-sdk.sh ../Rack-SDK lin-x64   # or win-x64, mac-x64, mac-arm64
make -C vcv RACK_DIR=../../Rack-SDK install

The panel is generated: make panel writes res/ComplexOsc.svg, res/panel-preview.svg (with stand-in knobs and jacks) and src/PanelLayout.hpp from one table, so the widget positions can't drift from the artwork. Every sigil is drawn from code (no fonts or images), so it renders in Rack and scales cleanly to a printed panel. It uses real Eurorack dimensions (16 HP × 128.5 mm), so it's also a starting point for a physical panel.

Design notes

• Wavefolder DC: symmetry biases a sine folder, which creates DC. A high-pass alone re-centres the wave and pushes peaks to about ±8 V. Because the core is a sine, the DC is exactly sin(a·b)·J0(a), so it's subtracted analytically (a small J0 table), with no limiter and no added aliasing.
• Through-zero FM: the primary phase increment is allowed to go negative. The phasor wraps in both directions.
• Self-feedback is phase modulation by the primary's own output, averaged over the last two samples (the DX7 trick). Without the average, feedback "hunts" at Nyquist and turns to hiss far too early.
• Chaos feeds the primary's output into the modulator's frequency, clamped to ±20 kHz so heavy settings can't push it far past the band limit.
• Unison stacks up to four primary voices before the wavefolder, so the fold intermodulates them (the growl a single voice can't make). Every voice gets the same through-zero FM and its own self-feedback history. An idle voice shadows voice 0, so it fades in exactly in phase and only spread or drift pull it away; with no spread, four voices sound like one. Detuned sines this close look like one sine with a beating amplitude A, so the folder's DC becomes sin(a·b)·J0(a·A), with A tracked per sample from the voices' phasors; that keeps the beat from leaking through as a slow wobble.
• Macros are piecewise-linear curves in dsp/Macros.hpp, applied by dsp/Panel.hpp, the one mapping from panel to engine that the firmware, the plugin and the patch renders all share. MALICE brings in a little FM of its own because chaos only reaches the primary through FM; without it, MALICE alone would stop at a saw. Chaos is a tipping point, so its curve is stretched to put the edge across 0.55–0.8 of the knob rather than one 5% step.
• Lorenz is integrated with a midpoint (RK2) step capped at 0.02, with a reset guard, so no setting can make it run away or produce NaN.
• CPU: cost is dominated by two 129-tap decimators. If the CPU meter says you need headroom, cascaded half-band filters are the next optimization.

Contributing

Bug reports, DSP fixes, tests and new ways to misbehave are welcome. Read CONTRIBUTING.md first; make check runs the lint, host tests and panel check that CI runs. This project follows the Contributor Covenant. Report security problems privately, as described in SECURITY.md.

License

MIT © 2026 Ross Edman. The vendored fonts in docs/assets/ are under the SIL Open Font License.