GDVP Oscillator
Oscillator — GDVP_NODE_OSCILLATOR ✅
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The tone generator. A LUT-based oscillator with a 32-bit phase accumulator (for >90 dB SNR),
six waveforms, linear FM, pulse-width control, per-read detune, and intrinsic pitch glide.
Source: gdvp_dsp_oscillator.c, payload gdvp_node_osc_t in gdvp_nodes.h.
Signal & ports
- Output (port 0): audio (
int16_t). - Mod input: a
mod_buffercarries audio-rate linear FM when another node is wired into the oscillator's modulation input. FM depth is set byfm_depth_cv. - Pitch is not a wire — it comes from the played note (via the voice) plus the parameters below.
Parameters
| Parameter | Param ID / patch key | Range | Meaning |
|---|---|---|---|
| Waveform | patch waveform |
0–5 | 0=Sine, 1=Square, 2=Triangle, 3=Sawtooth, 4=Pulse, 5=Noise |
| Pitch (note CV) | GDVP_PARAM_PITCH_CV / patch pitch |
0–16383 | Target pitch as 14-bit CV; 128 CV = 1 semitone, 8192 = centre |
| Pitch target | GDVP_PARAM_PITCH_TARGET |
0–16383 | Glide target for the slew limiter (see pitch) |
| Portamento / glide | GDVP_PARAM_OSC_PORTAMENTO |
0–255 | 0 = instant snap, higher = slower exponential glide |
| FM depth | GDVP_PARAM_OSC_FM_DEPTH_CV (NRPN 1/0) |
0–16383 | Linear FM index from the mod input |
| FM ratio | GDVP_PARAM_OSC_FM_RATIO_CV (NRPN 1/1) |
0–16383 | Carrier:modulator ratio |
| Pulse width | patch pulse_width / GDVP_PARAM_OSC1_PWM_CV |
0–16383 | 8192 ≈ 50% square; for Pulse/Square shaping |
| Amplitude | GDVP_PARAM_OSC_AMPLITUDE_CV / patch amplitude |
0–16383 | Oscillator output level |
| Detune | GDVP_PARAM_OSC_DETUNE_CV / patch detune |
−128…+127 (stored signed) | Read-time detune, ±1 semitone, ~1 cent/step — see detune |
| Hard reset | GDVP_CMD_HARD_RESET (command) |
— | Snaps phase + pitch instantly (cold strike) |
Patch files store
pitch,detune,amplitude, etc. as the field values shown in the example library.detuneappears as a large unsigned number in some patches (e.g.8128) because of how the UI offset is encoded; treat the audible result as a small ±cents trim.
Behaviour notes
Pitch slewing — glide that is musically correct
The oscillator keeps a high-precision smoothed_pitch_cv (Q16.16) that chases the
target_pitch_cv via an EMA whose rate is portamento_shift. Because the engine slews the
linear pitch CV and pitch→frequency is exponential, the resulting frequency contour is an
exponential glide with (approximately) constant glide time regardless of interval — the correct
behaviour for portamento. With portamento_shift = 0, or on a HARD_RESET, the pitch snaps
instantly. This is the mechanism behind MONO/LEGATO glide.
Detune vs. pitch — calibration separated from intent
GDVP deliberately separates musical intent (the note → target_pitch_cv) from hardware
calibration (the detune knob → detune_bias). Detune is applied additively after the
portamento EMA, every read, with hard saturation to protect the LUT. Range is ±128 CV steps =
±1 semitone at roughly 1 cent per step. This means detuning never disturbs the glide target and
two oscillators can be fanned a few cents apart for analog thickness without affecting tracking.
Noise waveform
Waveform 5 uses a dedicated per-oscillator PRNG (prng_state) with a sample-and-hold latch
(noise_latch) for phase-synced noise. For richer noise/particle sources (colored noise,
Poisson dust, sample-and-hold voltages) use the dedicated Exciter node.
Anti-aliasing
The implemented waveforms use LDF-BLEP-style band-limiting on the discontinuous shapes (square/saw/pulse) so high notes don't alias harshly. For very bright patches the oscillator may run oversampled, in which case the compiler inserts up/down-samplers around it.
Related
- Performance: glide · Parameters: pitch CV
- Modulate pitch/PWM from an LFO (vibrato/PWM) or Envelope.