LFO — `GDVP_NODE_LFO` ✅

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A multi-timescale low-frequency oscillator — a "time synthesis engine" that derives three modulation layers (meso, micro, macro) from a single shared phase, with organic chaos drift and key-sync. It shares the oscillator's phase machinery but adds depth-layered output. Source: gdvp_dsp_lfo.c, payload gdvp_node_lfo_t in gdvp_nodes.h.

Signal & ports

Output (port 0): a modulation signal, wired into any modulatable input — a filter port 1 (filter sweep), an oscillator (vibrato / PWM), a VCA (tremolo).
Mod input: an external CV can modulate the LFO rate linearly (FM of the LFO).

Parameters

Parameter	Patch key / field	Range	Meaning
Shape	`shape`	0–5	`0`=Sine, `1`=Square, `2`=Triangle, `3`=Saw, `4`=Sample&Hold, `5`=Noise
Rate	`rate` (`target_rate_cv`)	0–16383	Base rate, logarithmically mapped via `GDVP_LUT_LFO_INC`
Meso depth	`meso_depth`	0–16383	Rhythm/gesture layer (1× the base phase)
Micro depth	`micro_depth`	0–16383	Texture layer (16× rate, toward audio-rate shimmer)
Macro depth	`macro_depth`	0–16383	Evolution/drift layer (filtered chaos)
Inertia	`inertia` (`rate_inertia`)	0–15	Rate-slew EMA shift; `0` = instant, higher = sluggish/organic
Sync mode	`sync_mode`	0–2	`0`=Free, `1`=Transport sync, `2`=Key sync
Polarity	flag bit0	uni/bi	Bipolar vs unipolar output

Behaviour notes

Three timescales from one phase

A single 32-bit global_phase advances each sample; the kernel reads it three ways at zero extra cost: the meso layer indexes the phase directly (1×), the micro layer uses phase << 4 (16× faster, for shimmer/texture), and the macro layer is a one-pole EMA-filtered xorshift chaos source that slowly modulates the effective rate (drift/evolution). The three depths are perceptually squared (depth² >> 14) before mixing so crossfading between layers sounds smooth rather than abrupt. Set a single layer for a conventional LFO; combine them for evolving, non-repeating modulation.

Logarithmic rate + inertia

Rate CV is mapped logarithmically through a LUT, so the knob feels even across a wide span (sub-Hz drifts up to fast shimmer). rate_inertia slews the rate change itself — turn it up and rate moves glide rather than jump, which is what gives the LFO its "organic" feel.

ℹ️ When you'll hear it (and when you won't). SLEW MASS only acts while the rate is changing — a knob move, a MIDI CC, or DAW automation. On a static rate it is silent by design: it is a glide on rate transitions, not a modifier of the steady tone. To hear it, hold a note and sweep FREQUENCY with SLEW MASS at zero, then again at maximum — the second sweep arrives noticeably late (about ¾ s of lag at full mass). Key-sync note-ons snap the rate, so per-note restarts are always immediate regardless of mass.

Sync

Key sync (mode 2): ✅ works. A HARD_RESET (note-triggered) zeros the phase and snaps the smoothed rate, so the LFO restarts in phase on each note — essential for consistent per-note vibrato onset.
Transport sync (mode 1): ⚠️ not yet active. The LFO kernel currently receives the transport tick_mask but casts it to (void) (a comment marks this "Phase 2"). So selecting transport-sync does not yet lock the LFO to tempo on this build. See Performance: tempo and Appendix A.

Sample & Hold / Noise shapes

Shapes 4 and 5 use the LFO's own xorshift PRNG (prng_state) and a sh_latch, giving stepped random (S&H) and noise modulation without an external source.

Vibrato → wire to Oscillator pitch; tremolo → wire to VCA; filter sweep → wire to Filter port 1.
Examples: lfo_vibrato, lfo_tremolo, lfo_pwm, lfo_filter_sweep (library).