V-SidechainListener

What it is

V-SidechainListener is a sidechain routing monitor. With Listen to Sidechain enabled and an active sidechain bus, it replaces the main output with the sidechain signal and applies the selected power-of-two (BS) gain. With Listen to Sidechain disabled, or when no active sidechain is available, the main input passes through unchanged. The switch and gain are intentionally instant and are not smoothed.

Controls & parameters

Control	Range or choices	Default	Function
Listen to Sidechain	On/Off	On	When on and sidechain audio is active, routes the sidechain to the main output. When off, keeps the main input. If no sidechain is active, the main input remains the output even when this is on.
Sidechain Level / Sidechain Gain	-16 to +16 BS, whole steps of 1 BS	0 BS	Scales only the monitored sidechain with `2^gain`. At 0 BS the multiplier is 1; +1 BS doubles it and -1 BS halves it. This is a power-of-two (BS) ratio control, not a dB parameter.

The status LED and text are informational rather than parameters. They report LISTENING TO SIDECHAIN, SIDECHAIN READY, or NO SIDECHAIN CONNECTED.

Workflow / how to use it

Insert V-SidechainListener on the track whose main signal should remain available as the fallback output.
In the host, route the signal that a keyed compressor, gate, or dynamic processor should hear to the plugin’s sidechain input.
Leave Listen to Sidechain on and watch the status. LISTENING TO SIDECHAIN means the active sidechain is being monitored; NO SIDECHAIN CONNECTED means the main input is still passing through.
Adjust Sidechain Level in BS if the key signal is too quiet or too loud to audition. Use +1 BS to multiply by exactly 2, or -1 BS to multiply by exactly 0.5.
Turn Listen to Sidechain off when finished checking the routing. The main signal then passes through unchanged.

Use cases

Audition a compressor key: Hear the kick, vocal, or other signal that a keyed compressor is receiving before changing the compressor settings.
Level-match a sidechain: Use the BS control to double or halve the monitored signal while checking a quiet or overly strong key. The main signal is not changed by this gain.
Debug routing: Confirm whether the host has enabled and supplied the sidechain bus. The status text distinguishes an active listener from a ready bus and a missing sidechain.
Check a fallback path: With no sidechain connected, or with Listen to Sidechain off, verify that the main input remains intact while the routing is configured.

Specs & requirements

Formats: AU and VST3.
Audio I/O: The configured buses are stereo main input, stereo sidechain input, and stereo output. The source layout validator accepts mono or stereo main input/output layouts when they match; the sidechain bus must be enabled and contain channels for monitoring.
Latency: Zero processing latency. The processor reports a zero-second tail.
Sample rates: No fixed sample-rate list is declared by the plugin source.
Precision: The processor implements the float processing path; no double-precision processBlock override is provided.
MIDI: No MIDI processing is enabled.
State: Listen to Sidechain and Sidechain Gain are stored as APVTS XML state. The plugin exposes one host program and does not implement preset programs.
Platform: Workspace audio-toolbox build guidance targets macOS 10.15 or later.

Notes / caveats

BS is the power-of-two (BS) control. Its exact multiplier is 2^gain, so it is based on doublings and halvings rather than a dB value. Unlike V-Shift, this is a floating-point multiplier rather than direct IEEE-754 exponent-field manipulation.
Gain is applied only when sidechain audio is actually selected for the output. It does not alter the main input fallback path.
The host must expose, enable, and feed the sidechain bus. If it does not, V-SidechainListener cannot monitor that signal and passes the main input through.
Parameters switch immediately with no smoothing. This is useful for routing checks but can also make abrupt output changes audible.
The status indicator reports routing state; it is not a level meter.