Audio mix

How clips reach the speakers and the export: clip gain, channels, track faders, the master, and loudness normalize.

Every clip runs through the same chain in preview and export: source → channels (audioChannel / channelMode) → gain (dB) → clip fx → volume (keyframes, fades, duck) → pan → its A-track, then track fx → track fader → track pan → master sum → master fx → master fader. A track has a fader (tracks[].gain, dB), a pan (tracks[].pan) and effects (tracks[].fx); the master has a fader (master.gain) and effects (master.fx). Audio on a video lane (a clip with volume > 0 on V1…) goes straight to the master. In the UI these are the strips in the Mixer tab beside the Inspector (its FX button edits that track's or the master's effects); mute / solo are the existing track switches (disabledTracks).

Effects (fx - an array processed in order; every parameter optional, out-of-range values are clamped; on:false bypasses one without losing its settings):

type	parameters (default)
`eq`	`lowFreq` 120 Hz, `lowGain` 0 dB (low shelf) · `midFreq` 1000, `midGain` 0, `midQ` 1 (peak) · `highFreq` 8000, `highGain` 0 (high shelf); gains −18…+18
`highpass` / `lowpass`	`freq` (80 / 8000 Hz), `q` 0.71
`compressor`	`threshold` −20 dB, `ratio` 4, `attack` 10 ms, `release` 200 ms, `knee` 6 dB, `makeup` 0 dB
`limiter`	`ceiling` −1 dB, `release` 80 ms - brickwall, 5 ms lookahead; nothing passes the ceiling
`gate`	`threshold` −50 dB, `range` −40 dB (how far it closes), `attack` 2, `hold` 80, `release` 150 ms
`delay`	`time` 0.3 s, `feedback` 0.35, `mix` 0.25
`reverb`	`decay` 2 s, `predelay` 20 ms, `mix` 0.25
`distortion`	`drive` 0.3, `mix` 1
`widener`	`width` 1.5 (0 = mono, 1 = as is, 2 = extra wide)

Presets fill the chain with tweakable effects: Voice - clean-voice, podcast, radio, deep-voice (EQ-only: lower, warmer - not a pitch shift), telephone; Music - cinematic, wide, muffled (next room). Agents apply them (or any chain) with the patch op setFx: {op:"setFx", target:"clip", id:"c_vo", preset:"podcast"} · {op:"setFx", target:"track", id:"A3", fx:[{type:"eq", highGain:-3}]} · {op:"setFx", target:"master", fx:[{type:"limiter", ceiling:-1}], append:true} · fx:null clears. On a clip it applies to its linked stems too; chains are validated (unknown effect or preset → the whole patch is refused). The compact project view shows chains as fx:highpass·eq·….

Set a track fader / pan: {op:"setTrack", id:"A2", set:{gain:-8, pan:0}} (null or 0 resets). Master: {op:"setProject", set:{master:{gain:-1}}}.
Normalize - fablecut_normalize_audio {clipIds, mode?:"lufs"|"peak", target?} measures each clip's source window after its channel routing (ITU-R BS.1770 integrated loudness with EBU R128 gating, or sample peak) and sets props.gain to hit the target. Linked stems are measured together and share one gain; passing a video clip normalizes its stems. Targets: −14 LUFS streaming / social, −16 LUFS podcast / dialogue, −23 LUFS broadcast, or mode:"peak", target:-1. Locked clips are skipped unless force:true. The inspector's Normalize in the editor does the same measurement.
Fade curves - a fade transition on an audio clip may carry curve: "power" (constant power - the crossfade default, no dip in the middle), "linear" (constant gain - for crossfading the same material, e.g. a split of one take) or "exp" (slow start, natural fade to silence). No curve keeps the original eased shape. Only the volume follows the curve; picture fades are unchanged. {transitionOut:{type:"fade", duration:3, curve:"exp"}}.
Crossfades - overlap A and B on one track and give A transitionOut:{type:"fade", duration:d, curve:"power"} and B transitionIn the same, with d = the overlap. Shift+D in the editor does it for you: it borrows the overlap from spare media on both sides of the cut (half each, or more from the side that has it), so nothing after the cut moves; for a linked shot the stems crossfade and B's picture dissolves in.
Auto-duck - fablecut_auto_duck {clipIds:[music…], under?:["A1"], amount?:-12, threshold?:-40, attack?:0.3, release?:0.6} finds where the voice tracks (default: every other audio track) are above threshold dBFS - short gaps are bridged so the music doesn't pump between words - and writes keyframes.duck on the music: ramp down attack s before speech, hold, back up over release s. It replaces earlier ducking; amount:0 clears it. Same as the inspector's Auto-duck section or the clip menu's Auto-duck under other tracks.
In the editor, each audio clip shows its volume line (yellow; dashed = after ducking): drag it to change the level, Ctrl/Cmd-click to add a keyframe, drag a point to move it, Alt-click or double-click to remove one. The corner fade grips drag a constant-power fade in or out. Both edit linked stems together.
Use gain for "this clip is too quiet / loud", volume keyframes for shaping, duck for dipping under dialogue, and the track fader to balance whole lanes (dialogue against the music bed).

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