polyhelm

polyhelm · sources · schema v1

POLYHELM — HELM with a polyphonic (poly bus) input. The full HELM polyphonic subtractive synth (algorithm port of Matt Tytel's Helm; originally GPL-3.0, this port AGPL-3.0-or-later) reusing HELM's entire DSP engine (shared packages/dsp/src/lib/helm-engine.ts) — the same 4-8 voice allocator, 2 morphing oscillators with transpose/tune/unison, sub + noise, Cytomic TPT state-variable filter (12/24dB, LP↔BP↔HP blend, drive, key-track), three ADSR envelopes (amp/filter/mod), two pre-wired LFOs, 16-step gate-clocked step sequencer, and stereo voice-spread as HELM. The difference: POLYHELM ALSO accepts the project's 10-channel polyPitchGate poly bus on its POLY input, so a chord from MIDI LANE / POLYSEQZ / a chord sequencer plays it polyphonically — lane i drives one allocator voice (the DX7 pattern). Each lane's gate rising edge is a note-on at the lane's pitch and the falling edge a note-off; the played pitch is held on the voice so the ADSR release tail sounds at the played note (not C4) — held-pitch-through-release is correct because the pitch lives on the persistent voice, not a per-block cache. While a lane stays gated its pitch is tracked live (pitch glide / bend). The mono pitch_cv (V/oct) + gate fallback path still drives a single voice when no poly/MIDI source is patched (HELM-compatible), and the gear-icon Web MIDI settings panel works identically (device picker + per-channel rx). MIDI + poly + mono-CV can coexist (MIDI/CV use a non-lane allocator slot). The shipped HELM module is unchanged; POLYHELM is HELM + poly, not a stripped variant.

POLYHELM is the HELM polyphonic subtractive synth — a faithful port of Matt Tytel's open-source Helm — with a true POLY input bus. It is a full voice: two morphable oscillators plus a sub and a noise source, a multi-mode state-variable filter, three ADSR envelopes (amp / filter / a free 'mod' env), two LFOs, and an internal step sequencer, mixed across up to 8 allocator voices into a stereo output. The whole point vs. plain HELM is the `poly` input: feed it the project's 10-channel poly bus from a real polyphonic source (MIDI LANE in poly mode, POLYSEQZ, or a chord sequencer) and each gated lane lights up its own voice so it plays genuine chords. A mono pitch+gate pair is the single-voice fallback when nothing polyphonic is patched, and a hardware MIDI keyboard can also play it via the card's Web-MIDI gear panel. Every panel knob maps to the same Helm parameter it does in the standalone module, so patches/MIDI-learn transfer.

the faceplate

5 inputs · 2 outputs · 48 params

about this module

Hover a control, or open the patch panel and hover a jack.

inputs

id	cable	what it does
`poly`	polyPitchGate	The preferred polyphonic input: the 10-channel poly bus (5 lanes of pitch + gate) from MIDI LANE / POLYSEQZ / a chord sequencer. Each gated lane drives its own Helm voice, so POLYHELM plays chords. This MUST be fed by a real poly source to hear polyphony — patch MIDI LANE → poly, or POLYSEQZ → poly. While any lane is gated this bus takes priority over the mono PITCH/GATE fallback. poly pitch+gate bus; 10-channel poly bus (5 pitch + 5 gate lanes)
`pitch_cv`	cv	Mono V/oct pitch — the single-voice fallback used when nothing is patched into POLY (and no MIDI). Sets the pitch of the one voice the GATE input articulates. control voltage (CV)
`gate`	gate	Mono gate for the single-voice fallback: a rising edge starts a note (envelopes attack), and the falling edge releases it. Used together with PITCH when POLY/MIDI are not driving the synth. gate / trigger
`midi_in`	cv	A visual-only MIDI marker port. Actual MIDI flows in over the Web-MIDI API via the card's gear/settings panel (device + channel picker), not through a patch cable — this jack just shows that MIDI is a supported source. control voltage (CV)
`seq_reset`	gate	Reset trigger for the internal step sequencer: a rising edge restarts the modulation sequence from step 1, re-syncing it to your groove. gate / trigger

outputs

id	cable	what it does
`out_l`	audio	Left channel of the mixed polyphonic voices (after the stereo SPREAD). Pair with OUT R to keep the width. audio signal
`out_r`	audio	Right channel of the mixed voices, the partner of OUT L. audio signal

params

id	label	range	default	curve
`voiceCount`	Voices	1..8	6	discrete
`volume`	Vol	0..2	0.7	linear
`osc1Wave`	O1 Wav	0..3	0	discrete
`osc1Trans`	O1 Tr	-24..24st	0	linear
`osc1Tune`	O1 Tu	-100..100c	0	linear
`osc1Unison`	O1 Uni	1..7	1	discrete
`osc1Detune`	O1 Det	0..50c	10	linear
`osc1Vol`	O1 Vol	0..1	0.8	linear
`osc2Wave`	O2 Wav	0..3	1	discrete
`osc2Trans`	O2 Tr	-24..24st	0	linear
`osc2Tune`	O2 Tu	-100..100c	7	linear
`osc2Unison`	O2 Uni	1..7	1	discrete
`osc2Detune`	O2 Det	0..50c	10	linear
`osc2Vol`	O2 Vol	0..1	0.6	linear
`subWave`	Sub W	0..3	3	discrete
`subVol`	Sub V	0..1	0.4	linear
`noiseVol`	Noise	0..1	0	linear
`filterCutoff`	Cut	20..20000Hz	4000	log
`filterRes`	Res	0.5..16	1	linear
`filterBlend`	Mode	0..2	0	linear
`filterStyle`	Pole	0..1	0	discrete
`filterDrive`	Drv	0.5..6	1	linear
`filterKeyTrack`	Key	-1..1	0	linear
`ampAttack`	A A	0..8s	0.005	linear
`ampDecay`	A D	0..8s	0.2	linear
`ampSustain`	A S	0..1	0.6	linear
`ampRelease`	A R	0..8s	0.3	linear
`filAttack`	F A	0..8s	0.005	linear
`filDecay`	F D	0..8s	0.5	linear
`filSustain`	F S	0..1	0	linear
`filRelease`	F R	0..8s	0.3	linear
`filEnvDepth`	F Dpth	-1..1	0	linear
`modAttack`	M A	0..8s	0.005	linear
`modDecay`	M D	0..8s	0.5	linear
`modSustain`	M S	0..1	0	linear
`modRelease`	M R	0..8s	0.3	linear
`modEnvDepth`	M Dpth	-1..1	0	linear
`lfo1Wave`	L1 W	0..3	3	discrete
`lfo1Freq`	L1 Hz	0.01..30Hz	1	log
`lfo1Amp`	L1 Amt	0..1	0	linear
`lfo2Wave`	L2 W	0..3	3	discrete
`lfo2Freq`	L2 Hz	0.01..30Hz	4	log
`lfo2Amp`	L2 Amt	0..1	0	linear
`stepNumSteps`	Steps	1..16	8	discrete
`stepRate`	St Hz	0.1..30Hz	4	log
`stepSmooth`	St Smth	0..1	0	linear
`stepDepth`	St Dpth	-1..1	0	linear
`spread`	Spr	0..1	0.3	linear

controls

control	what it does
A A	Amp envelope ATTACK time (s) — how fast each note rises to full from note-on.
A D	Amp envelope DECAY time (s) — fall from the attack peak down to the sustain level.
A R	Amp envelope RELEASE time (s) — fade to silence after the gate falls.
A S	Amp envelope SUSTAIN level (0..1) — the level held while the note's gate stays high.
F A	Filter envelope ATTACK time (s) — how fast the filter-cutoff modulation rises on note-on.
F D	Filter envelope DECAY time (s) — fall to the filter-env sustain level.
F Dpth	Filter envelope DEPTH (−1..+1) — how much (and which polarity) the filter envelope sweeps the cutoff; 0 = no sweep.
F R	Filter envelope RELEASE time (s) — how fast the filter modulation fades after the gate falls.
F S	Filter envelope SUSTAIN level (0..1) — held filter-modulation level while the gate is high.
Mode	Filter mode blend (0 = low-pass, 1 = band-pass, 2 = high-pass) — morphs the state-variable filter response continuously.
Cut	Filter cutoff/corner frequency (20 Hz..20 kHz, log) — the main brightness control; the filter envelope and key-track add to it.
Drv	Filter input drive (0.5..6) — pushes the filter harder for saturation and a fatter, dirtier tone.
Key	Filter keyboard tracking (−1..+1) — how much the played note offsets the cutoff, keeping timbre consistent across the keyboard (positive opens the filter for higher notes).
Res	Filter resonance (0.5..16) — emphasises the cutoff frequency; high values self-oscillate.
Pole	Filter pole/style — switches the filter slope/character (a 1-pole vs steeper response).
L1 Amt	LFO 1 amount/depth (0..1) — how much LFO 1 modulates its destination.
L1 Hz	LFO 1 rate (0.01..30 Hz, log).
L1 W	LFO 1 waveform (sine / triangle / saw / square).
L2 Amt	LFO 2 amount/depth (0..1).
L2 Hz	LFO 2 rate (0.01..30 Hz, log).
L2 W	LFO 2 waveform (sine / triangle / saw / square).
M A	Mod envelope ATTACK time (s) — the free assignable envelope, used as a modulation source.
M D	Mod envelope DECAY time (s).
M Dpth	Mod envelope DEPTH (−1..+1) — the amount of the free mod-envelope routed to its destination.
M R	Mod envelope RELEASE time (s).
M S	Mod envelope SUSTAIN level (0..1).
Noise	White-noise level in the mix (0..1) — adds breath/grit, useful for percussion and texture.
O1 Det	Oscillator 1 unison detune spread in cents — how far apart the stacked unison copies are spread.
O1 Tr	Oscillator 1 coarse transpose in semitones (−24..+24).
O1 Tu	Oscillator 1 fine tune in cents (−100..+100) for detuning between semitones.
O1 Uni	Oscillator 1 unison voice count (1..7) — stacks detuned copies for a fatter tone.
O1 Vol	Oscillator 1 level in the per-voice mix (0..1).
O1 Wav	Oscillator 1 waveform (sine / triangle / saw / square).
O2 Det	Oscillator 2 unison detune spread in cents.
O2 Tr	Oscillator 2 coarse transpose in semitones (−24..+24).
O2 Tu	Oscillator 2 fine tune in cents (−100..+100); default +7 c for a slight detune-beat against OSC 1.
O2 Uni	Oscillator 2 unison voice count (1..7).
O2 Vol	Oscillator 2 level in the per-voice mix (0..1).
O2 Wav	Oscillator 2 waveform (sine / triangle / saw / square).
Spr	Stereo SPREAD (0..1) — pans the voices across the field for width (0 = mono/center, up = wider).
St Dpth	Step-sequencer modulation DEPTH (−1..+1) — how much the step pattern modulates its destination; reset its phase with the SEQ RESET input.
Steps	Internal step-sequencer length (1..16 steps) — the modulation pattern's period.
St Hz	Step-sequencer rate (0.1..30 Hz, log) — how fast it advances through its steps.
St Smth	Step-sequencer smoothing (0..1) — glides between step values instead of stepping abruptly (0 = hard steps, up = slewed).
Sub V	Sub-oscillator level in the mix (0..1).
Sub W	Sub-oscillator waveform (sine / triangle / saw / square), one octave below — adds low-end weight.
Voices	Polyphony: the maximum number of simultaneous voices the allocator will sound (1..8). Lower it for mono/duo behavior or to save CPU; raise it for thicker chords.
Vol	Master output gain across all voices (0..2; 1 = unity).

source

polyhelm.ts on GitHub.