VCA — `GDVP_NODE_VCA` ✅

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The voltage-controlled amplifier: the level/gate stage of a voice. Q16.16 gain scaling with EMA convergence (so gain changes are click-free) and optional tanh saturation for soft drive. Source: gdvp_dsp_vca.c, payload gdvp_node_vca_t in gdvp_nodes.h.

Signal & ports

Audio in (port 0): signal to amplify.
Control in (port 1): gain/gate modulation — the amplitude envelope wires here in every stock voice; this is what makes notes start and stop.
Output (port 0): amplified audio.

Parameters

Parameter	Param ID / patch key	Range	Meaning
Gain	`GDVP_PARAM_VCA_GAIN_CV` / patch `gain`	0–16383	Output gain (14-bit), EMA-smoothed to the target
Saturation enable	`GDVP_PARAM_VCA_SATURATION`	0/1	Enable tanh soft-clip on the output
Mute	`GDVP_PARAM_VCA_MUTE`	0/1	Output silence (executes but emits zero)

Behaviour notes

Smoothed gain

Gain is tracked in Q16.16 and converges toward target_gain via an EMA, so automation and envelope control produce smooth amplitude changes rather than zipper noise. The convergence behaviour is verified by the engine's VCA convergence tests (test_gdvp_vca_convergence.c).

Saturation

With saturation enabled, the output passes through a LUT-based tanh curve (gdvp_lut_apply_tanh_saturation) for analog-style soft clipping without any runtime math. Use it to add warmth/limiting at the amp stage; for more aggressive or varied nonlinear shaping the GFX Gain node offers fold/µ-law/rectify curves.

Mute vs. bypass

Mute keeps the node in the execution plan but forces zero output. This differs from the node-level BYPASSED flag (DSP skipped for A/B) — mute is an audible silence you can automate.

Driven by the amplitude Envelope (port 1) and optionally an LFO for tremolo.
Feeds the Panner in a stereo voice.