signal_gain

NODE

Pulls the level down by what the aux bus says. This is how power supply sag is written.

Parameters

FIELD	WHAT IT DECIDES	RANGE	REQUIRED
depth_db	Sag depth [dB].	0 〜 24	yes

{
  "depth_db": 6,
  "type": "signal_gain"
}

How it is computed

the control value on the aux bus is mapped onto a reduction of up to depth_db
and applied to the main signal

aux = 0  →  gain = 1.0        nothing on the bus means nothing happens

Forgetting to wire it leaves the sound unchanged rather than silent. That is deliberate, and it is also why a chain that does nothing can still pass every check.

Using it

It needs an envelope_follower upstream.
Without one, the bus holds zero and this node does nothing at all. Both the shape check and the simulation pass in that state, so if the sound is not what you expected, look here first.
It is time varying, so it counts as nonlinear.
A chain containing it is simulated, arms the limiter and is soft started, exactly like one containing a saturator.
Depth has a ceiling for a reason.
Beyond it the node stops being sag and becomes a gate, which no longer fits the convention that a module passes the reference level at unity.