Crossfader Setup and Deck-Level Modulation

How your DJ app's crossfader is configured, and which controls you reach for to modulate deck levels during a mix, both shape how a loaded fusor behaves at runtime. The interaction applies in Manual, Mixed and Auto Run Mode: anything the fusor outputs to deck-level controls reaches the same destination whether progress is being driven by the crossfader or by a timer.

What follows is the three common setups, what each one implies for a running fusor, and the authoring pattern that lets a single fusor work cleanly across all three.

Three setups

There are three common ways to modulate deck levels during a transition. Each one is a working setup.

Setup 1: Crossfader live, crossfader controls deck levels

The crossfader is the primary deck-level control. As you move it from outgoing to incoming, your DJ app's crossfader-curve setting (constant power, linear, sharp, etc.) shapes the actual deck volumes. The deck-level faders stay at full.

Setup 2: Crossfader live, deck-level faders control deck levels

The crossfader is left near center and the two deck-level faders control the mix. The crossfader is still in the audio path, so on a constant-power crossfader curve a deck playing solo doesn't reach full volume. That is the cost of leaving a live crossfader near center. It keeps both the crossfader and the fader workflow available without opening the DJ app to change the bypass setting.

Setup 3: Crossfader in bypass, deck-level faders control deck levels

The crossfader is out of the audio path. Deck levels are driven by the deck-level faders alone, which gives the widest range of fine deck-level control with no crossfader curve on top of it.

Setup 2 and the crossfader

Setup 2 conflicts with how the Fusor player drives progress. The crossfader is the progress actuator: in Manual Run Mode your hand on it is what advances the transition, and on the clock, in Auto Run Mode and the first part of a Mixed run, the player moves it so it stays aligned with progress. "Leave the crossfader near center and mix on the deck faders" and "run a transition" cannot both be true of the same crossfader at the same time.

In practice that leaves you two workable ways to run Setup 2:

• Run in Auto Run Mode and let the Fusor player sweep the crossfader. You mix on the deck faders as usual; the crossfader travels on its own. On a live constant-power curve that travel is audible, so it becomes part of the transition.
• Switch to Setup 3 for the transition. With the crossfader in bypass, its travel is silent and the deck faders alone set the level. Per-app bypass toggles below can set it for you at the start of a run.

Setups 1 and 3 have no conflict. In Setup 1 the crossfader is meant to travel; in Setup 3 it is audibly inert, so whether the engine moves it has no audio consequence.

How a fusor behaves under each setup

What a loaded fusor actually does to your audio depends on whether it has a deck-level domain.

If the fusor doesn't modulate deck levels

The fusor leaves deck volumes alone. Deck levels come entirely from your DJ app, so whichever of the three setups you're in determines what happens. This is common for fusors that modulate EQ, stems or effects and leave volume to you or to the crossfader.

If the fusor modulates deck levels

The fusor's deck-level lanes emit MIDI to the deck-volume controls.

• Setup 1. The crossfader's curve and the fusor's lanes both change each deck's level, and the two multiply: with the channel fader and a linear crossfader both at 75%, the deck plays at just over 56%. This can be deliberate, if the author shaped the lanes assuming a normal crossfader underneath, or it can produce two curves working against each other.
• Setup 2. Same coexistence as Setup 1, with the addition above: the crossfader is travelling too, so its curve and the fusor's lanes are both moving the deck volumes.
• Setup 3. The fusor's lanes are the sole source of deck-level change during the transition. The crossfader is inert; the deck-level faders sit wherever the user left them.

Disabling the fusor's deck-level domain stops the fusor sending MIDI to those controls at all. The deck volumes are then governed by your DJ app's hardware (crossfader, faders) without any input from the fusor.

The constant-power deck-level pattern

A common authoring strategy is to include a deck-level domain with a constant-power curve in the fusor. The shape mirrors what most DJ apps' constant-power crossfader curves do: a smooth outgoing fade-out paired with a smooth incoming fade-in that sums to a roughly even total level across the transition.

When a fusor is authored this way, the user picks which setup they want and toggles the domain accordingly:

• Using the crossfader to control deck levels (Setup 1). Disable the deck-level domain. The crossfader handles volume; the fusor handles everything else. Output stays consistent, assuming the user's crossfader is also on a constant-power curve.
• Using the deck-level faders to control volume (Setup 2 or 3). Leave the domain enabled and the fusor's lanes modulate the deck levels during the transition; the user doesn't move the faders mid-mix. Or disable it and move the faders by hand.

This pattern lets one fusor work in all three setups. Some fusors are authored for one specific setup instead.

The levels a constant-power curve reaches are fader positions. How loud each position sounds depends on the channel-fader curve set in your DJ app; see Control Types → Positions, not decibels.

Deck levels and the mix point

A fusor's mix point indicates how its deck levels are authored. A standard constant-power crossfade crosses at the Middle: halfway through, both decks sit at about 71% and the summed level stays steady. At Start and End, one deck holds at full level while the other fades, so the pair sums louder than either track alone.

The Library has one Channel Fader fusor for each mix point:

Where the summed level rises, the fusor's Channel Fader card in Session View shows a preflight line saying so:

• Channel Fader (Start): Level jumps at the drop. You may need to adjust gain as the incoming comes in.
• Channel Fader (End): Level climbs before the cut. You may need to adjust gain as the incoming comes up.

Channel Fader (Middle) has no level preflight line. A fusor that imports one of these shapes as its deck-level domain brings its preflight line with it.

Per-app bypass toggles

Putting the crossfader into bypass and taking it back out by hand is cumbersome on many DJ apps: buried menu, modal dialog, easy to miss. Fusor Studio's example files include Traktor actions that set it over MIDI, and a fusor's pre-run actions can run it automatically at the start of a transition, so any fusor can declare its preferred bypass state and have it set without manual intervention.

Crossfader Bypass On and Crossfader Bypass Off are a pair for a bypass that lasts only as long as a transition. Crossfader Bypass Off writes a fixed layout. To put back a different layout, or decks C and D, copy the pair and have the first copy remember the assignments before switching them off and the second restore what it found. Bypass the Crossfader, and Put It Back walks through the example pair and builds those copies step by step, unlicensed, and Build a Constant-Power Crossfade wires it into a fusor as pre-run and post-run, with a channel-fader action on each side and the order each pair needs.