GDVP Envelope
Envelope — GDVP_NODE_ENVELOPE ✅
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A five-stage ADSR with independent curve shapes per stage, velocity scaling, legato and
retrigger behaviour, optional inversion, and a click-free, level-continuous release. Source:
gdvp_dsp_envelope.c, payload gdvp_node_env_t in gdvp_nodes.h.
Signal & ports
- Output (port 0): a control signal, typically wired into a filter port 1 (cutoff envelope) or a VCA port 1 (amplitude envelope / the "gate").
- The envelope is gated by the voice (note-on starts attack, note-off starts release).
Stages
Attack(0) → Decay(1) → Sustain(2) → Release(3) → End(4). Sustain holds until note-off; release
runs from wherever the level currently is, down to zero.
Parameters
| Parameter | Param ID / patch key | Range | Meaning |
|---|---|---|---|
| Attack rate | GDVP_PARAM_ENV_ATTACK_RATE / patch attack |
0–16383 | Time CV (see time curve); higher = slower |
| Decay rate | GDVP_PARAM_ENV_DECAY_RATE / patch decay |
0–16383 | Time CV |
| Sustain level | GDVP_PARAM_ENV_SUSTAIN_LEVEL / patch sustain |
0–16383 | Held amplitude (expanded to 16-bit internally) |
| Release rate | GDVP_PARAM_ENV_RELEASE_RATE / patch release |
0–16383 | Time CV |
| Attack curve | patch attack_curve |
0–3 | 0=Linear, 1=Log, 2=Exp, 3=Sigmoid |
| Decay curve | patch decay_curve |
0–3 | as above |
| Release curve | patch release_curve |
0–3 | as above |
| Velocity scale | patch velocity_scale |
0–65535 | How strongly note velocity scales output |
| Flags | (node flags) |
bitmask | bit0 Legato, bit1 Retrigger, bit2 Invert, bit3 Expressive, bit4 Release-now |
Behaviour notes
Time CV → rate, the x⁶ law
The staging pool stores canonical 14-bit time CVs, but the DSP needs a phase increment.
The conversion (gdvp_cv_to_env_rate) inverts the CV (so 0 = fastest, 16383 = slowest) and
applies an x⁶ polynomial expansion. The high exponent gives you fine control over short times
and a very wide overall range, matching how musical envelope times feel. A base increment of 1 is
always added so an envelope can never hang (the code calls this "Zeno's paradox protection").
Curve shapes
Each of attack, decay and release independently selects Linear / Log / Exp / Sigmoid via a LUT
(gdvp_lut_get_envelope). This lets you pair, say, a snappy exponential attack with a gentle
logarithmic release.
Click-free, C0-continuous release
Release computes a proportional drop from release_start_level — the exact amplitude at the
moment of note-off — down to zero. The first sample of release is therefore exactly the level
the envelope was at, guaranteeing no step discontinuity (C0 continuity) and no click, even if you
release mid-attack. This replaced an older inverse-LUT scheme that could jump levels.
Capacitor-charge retrigger
On a fast retrigger that begins near the peak, the attack rate is scaled up inversely with the
remaining gap so the envelope converges in well under a millisecond instead of crawling — a model
of V(t) = V_peak − (V_peak − V_start)·e^(−t/RC). Low starting levels use the normal rate. This
makes rapid re-triggered envelopes feel tight rather than sluggish.
Legato, retrigger, invert, expressive
- Legato (bit0): don't reset phase on an overlapping note — the envelope continues.
- Retrigger (bit1): restart the envelope on each note.
- Invert (bit2): output negative-going modulation (e.g. for inverse filter sweeps).
- Expressive (bit3): track continuous MPE pressure for per-note dynamics (Performance: MPE).
Oversampling
When the host voice is oversampled, envelope rates are halved with a guard that prevents a
non-zero rate from rounding to zero (GDVP_OS_RATE), so timing is consistent at 1× and 2×.
Related
- Wire to Filter port 1 for cutoff envelopes; to VCA port 1 for amplitude.
- Filter-specific envelope CCs (75–78) are listed on the Filter page.