GDVP License

Parameters

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6 · Parameters, Ranges & Values

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This chapter is the reference for values: the CV conventions, the scaling math, and the complete table of parameter IDs the engine exposes (gdvp_param_id_t in gdvp_parameter_bridge.h). For an alphabetical lookup see the Parameter Index.

6.1 The CV convention

Almost every continuous parameter is a 14-bit control value: integer 0–16383.

  • Unipolar parameters (cutoff, gain, amplitude, rate, level…): 0 = minimum, 16383 = maximum.
  • Bipolar parameters (pitch bend, modulation offsets, pan): 8192 = centre/zero, below is negative, above is positive.

The engine speaks 14 bits because that is high-resolution MIDI's resolution; a 7-bit MIDI CC is expanded to 14-bit on entry (see MIDI 14-bit). The UI knobs and the .gvp file use the same 14-bit currency, so a value is portable between knob, file and MIDI.

A few discrete parameters break the mould: enums (waveform 0–5, filter mode 0–3, slope 0–3), booleans (mute, saturation, pan law), and the detune field which is a signed 8-bit trim (±128 ≈ ±1 semitone). Voice-allocation params (glide, unison, arp…) are UI-space 0–255 or small enums, not 14-bit CV — see Performance.

6.2 Scaling math you can rely on

All integer, all deterministic (CR-001). The conversions that affect what you hear:

  • Pitch: 128 CV = 1 semitone, 1536 CV = 1 octave. A 14-bit pitch CV spans 128 semitones, centre 8192. (Concepts §1.3.)
  • Envelope time CV → rate: inverted (0=fastest, 16383=slowest) then x⁶ expansion, with a +1 floor so it can't hang. (Envelope §time.)
  • Filter cutoff CV → coefficient index: x³ perceptual curve so the sweep sounds even. (Filter §cutoff.)
  • LFO rate CV → increment: logarithmic via LUT. (LFO.)
  • Sustain CV → amplitude: 14-bit 0–16383 expanded to 16-bit 0–65535 by bit replication (no division). (Envelope.)

You don't compute these — you turn a knob and the engine applies the curve — but they explain why e.g. the bottom of the cutoff range isn't where the audible action is.

6.3 The bifurcated parameter model

This is the single most important idea for controlling GDVP live. Each modulatable parameter has two destinations in the node, written by two different paths:

Path Writes Math Example
Host / patch (macro) the base field absolute unsigned value UI cutoff knob → base_cutoff_q16
DSP / MIDI / LFO (micro) the modulation field bipolar offset centred at 8192 CC 74 / LFO → mod_cutoff_q16

The DSP merges base + modulation at audio rate. The consequences:

  • MIDI automation does not fight the knob. Sending CC 74 adds a bipolar offset around the knob's base position; 8192 over MIDI means "no change". Pull below 8192 to subtract, push above to add.
  • Patches store the base; performance rides the modulation. Loading a patch sets bases; your controller and LFOs ride on top without overwriting them.

The registry that enforces this (gdvp_param_registry[], gdvp_parameter_registry.h) holds two handlers per parameter — one for the host path, one for the DSP path — so the math can never drift between them.

6.4 Complete parameter ID table

Every entry in gdvp_param_id_t. "Domain" notes whether the value is unipolar 14-bit, bipolar 14-bit (centre 8192), or discrete. CC/NRPN columns show the default MIDI mapping where one exists (full MIDI map).

Core voice

Parameter ID Domain MIDI Target
GDVP_PARAM_PITCH_CV pitch 14-bit (note) Oscillator pitch — primary
GDVP_PARAM_PITCH_TARGET pitch 14-bit — Glide target
GDVP_PARAM_OSC_PORTAMENTO 0–255 — Glide rate
GDVP_PARAM_OSC_FM_DEPTH_CV unipolar NRPN 1/0 Oscillator FM depth
GDVP_PARAM_OSC_FM_RATIO_CV unipolar NRPN 1/1 Oscillator FM ratio
GDVP_PARAM_OSC_AMPLITUDE_CV unipolar — Oscillator amplitude
GDVP_PARAM_OSC_DETUNE_CV signed ±128 — Oscillator detune (±1 semitone)
GDVP_PARAM_OSC_BASE_PHASE_INC — — Deprecated (use PITCH_CV)

Filter

Parameter ID Domain MIDI Target
GDVP_PARAM_FILTER_CUTOFF_CV unipolar CC 74 Cutoff
GDVP_PARAM_FILTER_RESONANCE_CV unipolar CC 71 Resonance
GDVP_PARAM_FILTER_DRIVE_CV unipolar NRPN 2/0 Drive
GDVP_PARAM_FILTER_TYPE_CV discrete NRPN 2/1 Mode LP/BP/HP/Notch
GDVP_PARAM_FILTER_SLOPE discrete 0–3 — 6/12/18/24 dB/oct
GDVP_PARAM_FILTER_ATTACK_CV unipolar CC 75 Filter-env attack
GDVP_PARAM_FILTER_DECAY_CV unipolar CC 76 Filter-env decay
GDVP_PARAM_FILTER_SUSTAIN_CV unipolar CC 77 Filter-env sustain
GDVP_PARAM_FILTER_RELEASE_CV unipolar CC 78 Filter-env release

Amplitude envelope / VCA

Parameter ID Domain MIDI Target
GDVP_PARAM_ENV_ATTACK_RATE unipolar (CC 73) Envelope attack
GDVP_PARAM_ENV_DECAY_RATE unipolar — Envelope decay
GDVP_PARAM_ENV_SUSTAIN_LEVEL unipolar — Envelope sustain
GDVP_PARAM_ENV_RELEASE_RATE unipolar (CC 72) Envelope release
GDVP_PARAM_VCA_GAIN_CV unipolar — VCA gain
GDVP_PARAM_VCA_SATURATION bool — VCA tanh enable
GDVP_PARAM_VCA_MUTE bool — VCA mute

Per-oscillator extended (MIS canonical map)

Parameter ID Domain MIDI Target
GDVP_PARAM_OSC1_PITCH_BEND_CV bipolar CC 16 Osc1 bend offset
GDVP_PARAM_OSC1_PWM_CV unipolar CC 17 Osc1 pulse width
GDVP_PARAM_OSC1_SHAPE_CV unipolar CC 18 Osc1 waveform morph
GDVP_PARAM_OSC2_PITCH_BEND_CV bipolar CC 20 Osc2 bend offset
GDVP_PARAM_OSC2_PWM_CV unipolar CC 21 Osc2 pulse width
GDVP_PARAM_OSC2_SHAPE_CV unipolar CC 22 Osc2 waveform morph
GDVP_PARAM_OSC2_DETUNE_CV bipolar CC 23 Osc2 detune
GDVP_PARAM_OSC_MIX_CV unipolar CC 24 Osc1/Osc2 crossfade

Channel / global modulation

Parameter ID Domain MIDI Target
GDVP_PARAM_MOD_WHEEL_CV unipolar CC 1 Mod wheel
GDVP_PARAM_VOLUME_CV unipolar CC 7 Channel volume
GDVP_PARAM_PAN_CV bipolar CC 10 Pan

MPE / expression

Parameter ID Domain MIDI Target
GDVP_PARAM_PITCH_BEND_CV bipolar (pitch-bend) MPE pitch bend
GDVP_PARAM_CHANNEL_PRESSURE_CV unipolar (channel AT) MPE channel pressure
GDVP_PARAM_POLY_PRESSURE_CV unipolar (poly AT) MPE poly pressure

Mixer

Parameter ID Domain MIDI Target
GDVP_PARAM_MIXER_MASTER_GAIN unipolar CC 87 Mixer master
GDVP_PARAM_MIXER_INPUT_GAIN_0…5 unipolar CC 88–90 + Mixer inputs
GDVP_PARAM_MIXER_MUTE bool — Mixer mute
GDVP_PARAM_PAN_LAW bool — Panner law

Exciter

Parameter ID Domain Target
GDVP_PARAM_EXCITER_SOURCE_MODE discrete 0–4 Source family
GDVP_PARAM_EXCITER_COLOR discrete 0–4 Noise color
GDVP_PARAM_EXCITER_FLAGS bitmask Bipolar/Tempo/Gaussian/Crush
GDVP_PARAM_EXCITER_CRUSH_BITS small int Bit-crush depth
GDVP_PARAM_EXCITER_RATE unipolar S&H rate / density
GDVP_PARAM_EXCITER_LEVEL unipolar Output level
GDVP_PARAM_EXCITER_PARAM_A unipolar slew/steps/dust amp
GDVP_PARAM_EXCITER_DECORR_OFFSET unipolar Per-voice decorrelation

MIDI columns in parentheses (e.g. CC 72/73, channel/poly aftertouch) indicate controllers the canonical map or MIDI processor names but which are routed via generic sound-controller handling rather than an explicit per-parameter binding in gdvp_canonical_map.json. The explicit, guaranteed bindings are CC 1, 7, 10, 16–24, 71, 74–78, and NRPN 1/0, 1/1, 2/0, 2/1. See MIDI.

6.5 Discrete value cheat-sheet

Field Values
Oscillator waveform 0 Sine · 1 Square · 2 Triangle · 3 Saw · 4 Pulse · 5 Noise
Filter mode 0 LP · 1 BP · 2 HP · 3 Notch
Filter slope 0 = 6 · 1 = 12 · 2 = 18 · 3 = 24 dB/oct
Envelope curve (each stage) 0 Linear · 1 Log · 2 Exp · 3 Sigmoid
LFO shape 0 Sine · 1 Square · 2 Triangle · 3 Saw · 4 S&H · 5 Noise
LFO sync 0 Free · 1 Transport (⚠️ inactive) · 2 Key
Panner law 0 Linear · 1 Constant-power
Exciter source 0 Audio · 1 Particle · 2 S&H step · 3 S&H quant · 4 S&H smooth
Exciter color 0 White · 1 Pink · 2 Red · 3 Blue · 4 Violet
Voice mode 0 Mono · 1 Legato · 2 Poly · 3 Unison · 4 Duo · 5 Chord · 6 Delay · 7 Arp

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