Loading a fusor

Loading a fusor is how you set up the Fusor player. Pick a fusor, set the bars and BPM you want (if you're running in Auto Run Mode), and you're ready to arm.

You can load a fusor two ways: from the fusor picker in the Fusor player, or from the Fusors list view in the Library.

What "loading" means

Loading a fusor puts it in the Fusor player and changes nothing else. The Tempo Ramp setting already on the player is not changed, and the bars/BPM values (when shown) are not changed either.

• In Manual Run Mode the bars/BPM readout is not shown, since the crossfader drives the transition. It also disappears when you take over a run by hand mid-run, and when a Mixed run stops at its mix point.
• In Auto and Mixed Run Mode the bars/BPM readout is shown; check and set those values before arming, because Auto Run Mode uses them to time the transition.

Loading from the fusor picker

The fusor picker is the button in the picker row.

1. Click the fusor picker. The Library window opens, focused on the active collection's Fusors sub-tab.
2. Click the fusor you want. The Library window closes automatically and the fusor loads.

The Library window opens filtered to the active collection, shown as a collection chip in the filter bar. To find a fusor that is not in it, use the list the same way you would anywhere else in the Library: search, change the sort order, or remove the chip and add other filters (see Filtering a list). Clicking a row still loads it, and the active collection stays as it was.

Loading from the Fusors list view

1. Click the book icon in the toolbar to open the Library window. In its header, click Fusors. The Fusors section has two sub-tabs: Collections and Fusors. Switch to the Fusors sub-tab.
2. Use the search field, sort controls, and filters to narrow down to the fusor you want.
3. Right-click the fusor and choose Load, or double-click the row.

Each row also has a small info icon on the right that opens the fusor's editable detail view directly. The right-click menu holds the rest of what you can do with a row:

Add to Active Collection is refused when the fusor is a duplicate copy (see below): the status line reads Can't add "X - Copy.fusor": it's a copy of "X.fusor". Add "X.fusor" instead., and nothing is added to the collection.

To edit a fusor without loading it, use Details. Edits autosave. If the fusor you edit is the loaded one, the Fusor player reads it again after each save, so the edit applies from the next run. Saving the loaded fusor while it is armed disarms it, so finish the edit and arm afterwards. While the loaded fusor is mid-transition, its edits are paused until the transition ends. See Authoring Overview for the full editing model.

Files Fusor Studio can't read. A .fusor file that isn't valid JSON, or that parses but isn't a fusor, still shows up: a grayed row named after its file, sitting at the bottom of the list. Clicking or double-clicking it does nothing. Right-click it for Show in folder, which opens Explorer or Finder with the file selected, so it can be fixed or deleted there. Hover it for a tooltip naming the problem, for example "Can't read this file (not valid JSON). It reappears once fixed or synced. Right-click and choose Show in folder." Fusor Studio never modifies the file; fix it on disk and click Scan Folder (the refresh icon in the list header) to turn the row back into a normal one. A file saved with a leading byte-order mark, which some text editors and sync tools add, reads normally rather than showing as broken, and that holds everywhere Fusor Studio reads a fusor, including loading one into the Fusor player.

When the fusors/ folder itself can't be opened (a permissions problem, a sync app that's offline, or the folder replaced by a file), the list shows one grayed row with an orange folder icon reading "Can't open the Fusors folder". Hover it for a tooltip naming the problem, for example "Can't open this folder (no permission). The list updates when it opens. Right-click and choose Show in folder." Clicking or double-clicking it does nothing. Right-click it for Show in folder, which opens Explorer or Finder at your library folder with fusors selected. It sits last. Fusors from the last successful scan stay listed above it and still load. A newly created library with an empty fusors/ folder shows no such row.

Duplicate copies. If a fusor and a copy of it made outside Fusor Studio, such as an Explorer "name - Copy", a Finder "name copy" or a OneDrive conflict copy, both sit in the fusors/ folder, both rows show a small orange duplicate mark next to their name. Hovering either names the other file and confirms which one collections follow. See Authoring Overview → Where files live for how Fusor Studio decides which file is the original, and where else the mark appears.

Stem deck mark. A fusor that modulates stem parameters needs the deck in that role to be a stem deck. Its row has a small mark at the right end of the name, left of the mix point mark: a vertical bar with lines either side. The left side is the outgoing deck and the right side is the incoming deck. Four lines on a side means that deck must be a stem deck; one line means it need not be. Hover the mark for a tooltip: "Outgoing deck must be a stem deck", "Incoming deck must be a stem deck", or "Both decks must be stem decks". A fusor that controls no stems shows no mark. The mark stays when you switch a stem domain off, so the fusor still turns up under the Stems chip. To hide the mark, turn off Show stems glyph in Fusor lists in Settings ▸ General; the Stems chip and the Stems sort still work. Choose Stems in the list's Sort control to group fusors that need both decks as stem decks first, then the outgoing deck only, then the incoming deck only, then the rest, each group by name.

Filtering a list

The Fusors and Actions lists both have a filter bar above the rows. It works the same way in both.

Adding a filter. Click + in the filter bar. Choose Include or Exclude, then pick what to filter by: a collection, DJ app, mix point, or stems for fusors, a pack or DJ app for actions. The list narrows immediately and the filter appears as a chip in the bar.

DJ App chips. Both lists have a DJ App scope, with one chip per app in the tag registry ("Traktor," "Mixxx," and so on). A fusor or action that names no DJ apps is treated as working anywhere: an include chip never filters it out, no matter which app you've selected. An exclude chip only removes records actually tagged with that app, so an untagged record stays visible there too. An empty Built for field on a fusor, or Apps field on an action, means "works with every app," so a record with no apps listed always stays in the list.

Mix Point chips. The Fusors list has a Mix Point scope with four values: Start, Middle, End, and Not set. The option menu shows the mix point mark beside each of the three named values; Not set has no mark. The chip itself reads as a word, like every other chip in the bar, and takes Include or Exclude the same way the other scopes do.

None. The Collection filter's values start with None, and the Actions list's Pack filter does the same. Included, it keeps the fusors in no collection (the actions in no pack); excluded, it keeps the ones in at least one. The chip reads No collection or No pack. It is offered once you have at least one collection or pack.

Stems chip. The Fusors list has a Stems scope with one value, Stems, so choosing the scope adds the chip straight away. Any scope that offers only one value at that moment does the same. Included, it keeps every fusor that needs a stem deck on either side, the fusors that show the stem deck mark. Excluded, it keeps the fusors that need no stem deck.

Removing a filter. Click the × on an individual chip to drop just that one, or the × at the right end of the bar to clear all of them at once.

Combining filters. Two filters of the same kind widen the result: filtering by two DJ apps shows records made for either one, and two collections show the fusors in either. Filters of different kinds narrow it: a collection chip plus a DJ app chip shows only fusors that are in that collection and made for that app. Excluded filters always remove matching rows from whatever the other chips selected. The one thing the bar can't express is "either" across different kinds: there's no way to ask for "in this collection or for Traktor."

Filters from a right-click. Right-clicking a collection and choosing Show Fusors (or a pack and Show Actions) adds a chip for it, exactly as if you had added it with +. Any filters already in the bar stay, so this widens the list rather than replacing what you were looking at. The bar always names everything currently being shown, and the × clears it back to the full list.

Rows Fusor Studio can't read. Search always keeps them visible, and so does the DJ App chip. A Collection, Pack, Mix Point, or Stems chip hides one, since there's no membership, mix point, or stems to check it against. The row for a folder that can't be opened at all follows the same rule.

Example versions

Only example fusors and actions have version numbers, so a number marks a record as an example. The number follows the name in the Fusors and Actions lists, muted: v1, v2, and so on. A fusor or action with no number is your own, and an example you edit becomes your own and loses its number. Collections and packs have no numbers. How examples reach your library is in Setup → Your library and the example files.

A newer version of an example installs next to the older one. Each version is a separate fusor or action, and anything you built keeps the version it was built with until you switch it.

All versions. When your library holds an older version of an example, an All versions switch appears left of Sort in the Fusors and Actions lists. Off, the default, each example shows its newest version only. On, every version shows. An older version that a collection, a pack or a fusor's actions use stays listed with the switch off. The switch is not a filter chip: × at the end of the filter bar leaves it as it is, and it returns to off the next time the Library opens.

Show All Versions. Right-click a row and choose Show All Versions to list every version of that one example. A chip reading "name, all versions" appears in the filter bar; remove it with its ×. While the chip is on, every version of that example shows whatever the switch says.

Update mark. A blue update mark with an up arrow appears after a reference to an older version when a newer one is in your library. Hover it for the version it moves to. Click it to switch that reference to the newer version. The older version stays in your library. The mark appears:

• On a Fusors list row while a Collection chip is on and that collection holds the older version. The click switches it in every chipped collection that holds it, and the status line reads Updated "name" to version N in collection. The Actions list does the same with Pack chips.
• On a pad slot in the Pad Slot Editor.
• On a pre-run or post-run action row in the fusor editor. See Pre-run Actions.

Changing the active collection

The active collection is the one the fusor picker opens filtered to. To change it:

1. Open the Library window from the book icon in the toolbar and switch to the Collections sub-tab (under the Fusors section).
2. Right-click the collection you want and choose Set Active.

The fusor picker now opens filtered to this collection.

A .fcollection file Fusor Studio can't read shows the same way as a broken fusor: a grayed row named after its file, at the bottom of the Collections sub-tab. Clicking or double-clicking it does nothing. Right-click it for Show in folder, which opens Explorer or Finder with the file selected. Hover it for a tooltip naming the problem. Fusor Studio never modifies the file. Once the file is fixed, the row turns back to normal the next time the Collections list is opened, whether by switching to it or by opening the Library on it.

When the Collections folder itself can't be opened (a permissions problem, a sync app that's offline, or the folder replaced by a file), the sub-tab shows one grayed row with an orange folder icon reading "Can't open the Collections folder", with a tooltip naming the problem the same way, for example "Can't open this folder (no permission). The list updates when it opens. Right-click and choose Show in folder." Clicking or double-clicking it does nothing. Right-click it for Show in folder, which opens Explorer or Finder at your library folder with Collections selected. It sits last. A newly created library with an empty Collections folder shows no such row.

When you can't load

You can't load a new fusor while a transition is running. The Fusor player locks during a transition. Once the transition completes or you abort it, loading is available again. See Transport Controls.

What you'll see when a fusor loads

After you load a fusor, you should see:

• The fusor picker now shows the loaded fusor's name.
• The bars and BPM values on the Fusor player are unchanged (they're shown in Auto and Mixed Run Mode). These are not part of the fusor itself.
• The Tempo Ramp toggle is unchanged. Loading a fusor leaves it wherever you set it in the toolbar's transition group. The toggle resets to off at the end of every run, so it is off unless you turned it on for this run.
• A brief confirmation appears on the left side of the status line: "Fusor loaded: [name]".

Inspecting the loaded fusor: Session View

After a fusor is loaded, click the expand arrow in the toolbar (see The Player Window) to open Session View. This is an inline panel that opens between the toolbar and the picker row, so it appears above the Fusor player's controls; the window grows upward to make room for it, or downward when the player is sitting too near the top of the screen. It lets you read what the fusor will do (and make a few quick adjustments) before you arm.

Session View is a pre-flight staging surface: you load the fusor ahead of the run, read through it top to bottom, disable anything you do not want firing, adjust your DJ app by hand if the preflight notes ask you to, and then arm. It shows only what belongs to the fusor itself: its intent, the domains it modulates, and the actions it runs. Track- and tempo-specific detail (which only exists once a fusor is paired with two tracks in a transition) lives elsewhere.

Session vs record

Session View lets you adjust a loaded fusor to your rig, and saves each adjustment into the fusor. There are six adjustments, listed in full under What "session edits" cover. Each one is saved into the fusor as you make it. There is no Save button.

All six are judgments about your setup: which controls your DJ app has, which FX unit is free, which pre-run action your rig needs, which slot holds which effect, which fader curve suits the two tracks, and what the decks look like when the run ends. Your setup is usually the same next time.

A few things worth knowing:

• It overwrites. There is no "revert to what the author set". Once you switch a domain off, off is what the fusor says. If you want the original back, switch it on again.
• It only touches those six things. Curves, domains, actions and metadata are untouched; you edit those in the Library.
• It's locked during a run. You can adjust while armed, and once the transition starts everything is read-only until it completes or is aborted.
• Both windows can be open at once. Clicking the fusor's name opens it in the Library, and you can edit it there while it's loaded. Whichever change happens last is the one that is kept, and the other window updates to match. Saving the fusor in the Library while it is armed reloads it and disarms the Fusor player; during a run, the reload waits until the run ends.
• It is written to the file. A session edit goes straight into the .fusor on disk, at every license level, which is why there is no Save button here and nothing to discard.

The status line confirms each one: "3-Band EQ domain disabled.", "Incoming now routes through FX Unit 2.", and when a pick trades with the other side, "FX Units traded: incoming 2, outgoing 1."

When the write to disk fails (the file is read-only, held open by a sync app, or has gone missing), the edit still applies to this run: the domain or action switches off, the FX unit reassigns, the slot reorders, whatever you changed happens for as long as the transition is loaded. Only the save fails. In place of the usual confirmation, the status line reads an orange SES9-This run only: not saved to file, and the edit is gone the next time you load this fusor. See Status Messages for how to find and fix the cause.

The chronological stack

Session View is a single stack of cards, read top to bottom in performance order, the same order things actually happen during the run:

1. Pre-run actions (if any). They fire before the transition starts.
2. Domains, the body of the transition. Domain cards follow the general signal flow: stems, then EQ, filter, FX and Mixer FX, with the channel fader always last. Many effects act after the channel fader, an FX unit in Post Fader mode among them, so the order is approximate.
3. Post-run actions (if any). They fire when the transition finishes.

Above the stack, a short header shows the fusor's name, with its mix point as a small mark on the same row, right-aligned. It's the same mark the Fusors list uses (see Authoring Overview for what it means). A long name truncates to leave room for the mark; the mark itself never does. The mark is read-only here: the Mix Point picker on the fusor's detail page in the Library is still the only place it's set. Beneath the name sits the author's intent: a concise statement of what this fusor is for. Clicking the name jumps straight to the fusor's detail page in the Library window. (The intent line is only shown when the author wrote one.) The fusor's longer description and its authoring metadata (author, version, DJ apps) live on the fusor's detail page in the Library, off the performance surface.

Actions look different from domains. Action cards have a colored left border so you can tell at a glance which cards fire an action and which modulate a domain's parameters, even though they share the same card shape.

What every card shows

Whether it's an action or a domain, each card collapses to these things:

• An orange enable Switch. Turn it off to skip that card. The change is saved to the fusor.
• The name (domain name, or action name). For actions, clicking the name opens the action's detail page in the Library window.
• A derived line that Fusor Studio works out from the fusor itself. A domain card shows it only when the domain has a lane with a step set attached. A domain whose lanes are all continuous has no derived line. On an action card, the line appears for each SET step that writes a control with a fixed number of positions. See What the card says it will send.
• The card's pre-run text, if the author filled it in. For a domain this is the author's reminder for what that one domain needs (for example, "Set the EQ knobs to center before arming."); for an action it's the author's per-action note. Hidden when empty.

A card can also have orange warning lines, described under What the card says it will send, and a domain card shows its End of run setting in its title row.

Only one card is open at a time. Click a card to expand it; opening another closes the first.

What the card says it will send

Above the author's pre-run text, a card can show a line Fusor Studio computes from the loaded fusor. There is no field behind it and no way to edit it: it is worked out again every time the card is drawn, so it always matches the fusor as it currently is.

It names only the positions the fusor sends. For a stepped lane that is the positions its points sit on; for a SET step, its one value.

On a domain card there is one line per stepped lane, naming the positions that lane actually reaches, in the order it reaches them:

Outgoing FX2 Slot 1 Amount: 1/4 → 2/4 → 4/4
Incoming FX3 Slot 1 Amount: 1/4

The arrow means the lane moves between values. A lane with no arrow holds at one position for the whole transition. That's the common case, and it's worth reading closely: a lane you thought was sweeping looks exactly like this.

A stepped lane holds each point's value until the next point, so it sends only the values at its points, with no interpolation between them. A lane with one point at its lowest position and the next at its highest sends those two values, so the line names two positions even though the step set has seven.

Lanes that move continuously produce no line. An EQ band, a channel fader or a wet/dry knob has no positions to name. Enable switches produce no line either, since Off and On cannot be read in the wrong order.

When the outgoing and incoming sides of a domain do the same thing, they share one line. When they differ, in the positions they step through or in FX unit, each side gets its own line, prefixed Outgoing or Incoming.

Lanes on an FX unit name their unit. FX2 Slot 1 Amount is slot 1 of FX Unit 2. Two sides of one domain routed through different units read differently for that reason, which is what you want: without the unit number, two lines describing two different units are identical.

When the line is too long. A lane that steps through many positions won't fit at the Fusor player's width, so the middle is left out: Outgoing FX2 Slot 1 Amount: 1/4 … 16 bars. You get where it starts and where it ends. To read every position, expand the domain and look at the curve.

On an action card there is one line per SET step that writes to a control with a fixed number of positions:

Tempo Range Selector: 50%

Steps that read a control rather than write it (WAIT_UNTIL, IF) get no line, and neither does a SET nested inside an IF, since it may never fire.

Controls whose positions you named yourself lead with the position number:

Mixer FX Selector: position 2 (Reverb)

For a control like the tempo range, every position's meaning is fixed by the DJ application. For a control like the Mixer FX selector it is not: which effect sits in which slot is your setup, and the name in brackets is what the fusor's author believed about their rig. So the position, which is what actually gets sent, comes first, and the name comes after it as support. If the two disagree, trust the number and go and look.

It says position rather than slot. Traktor's Mixer FX ladder has five positions, but the first is the fixed Filter and only the other four are the slots you assign. Position 2 is your assignable slot 1.

When one action touches more than one deck. Most actions work on a single deck, and the line names the control on its own. When an action's SET steps reach two or more decks, each line gains a short deck prefix:

A: Tempo Range Selector: 50%
B: Tempo Range Selector: 10%

When those steps are written against roles rather than decks, the prefix names the side instead, Out: or In:. Which physical deck a role names can change until the transition starts, so the card names the side.

The lines show no counts, because a count beside a value is ambiguous: 1/4 beside 3 of 7 looks like one of four, and 3 of 7 reads as the third position just as easily as three positions out of seven.

Warning lines. An action card also shows a line in orange when reading the action turned up a step that names a position the control doesn't have, or a step that writes to a control that only reports its value and cannot be set. The warning names the address and the offending value. It doesn't stop the fusor loading or the action running: it tells you the action will fail at that step and report an error on the status line. Open the action in the Library to fix it. The same warnings cover a CAPTURE of a control that only reports its value, and a WAIT_UNTIL or IF that compares against a position the control doesn't have. Domain cards show their own orange lines for an effect that will make no sound, or that will be left on at the end; see FX Routing → Ending with the unit still open.

Expanding a domain card

Inside a domain's expanded panel you'll see the curves the domain will run, laid out in two columns, outgoing on the left and incoming on the right, so you can read what each side does. For FX-unit-typed domains, each side that has effect curves has a small numbered picker that lets you choose which FX unit (1–4) that side routes through. A fusor with effects on only one side shows one picker and uses one unit.

When both the outgoing and incoming sides have effect curves, the picker handles collisions for you: if you click the unit the other side holds, the two sides trade. Your side takes the unit you clicked, and the other side takes the one you just left. So you can re-balance FX routing on the fly without clearing the other side first. The status line names both halves, since one click moved two sides. Your pick is saved into the fusor, the trade included.

FX domains also let you drag a slot row by the grip on its right. That moves the curves onto the slot you drop them on, effect name and all. It's for the common mismatch where the author put their Flanger in slot 1 and your rig has it in slot 2: drag it down one, and the fusor modulates the slot you actually have it in. Saved into the fusor like the rest.

Hover a curve label to see a tiny preview of the curve shape, or click it for a larger one.

Expanding an action card

An action's expanded panel opens straight onto the action's body as a read-only text summary (the same text the action editor uses to display the steps). This is for sanity-checking what the action will do before you let it run. There's no editing here; open the action in the Library for that.

What "session edits" cover

There are six session edits in Session View:

1. Domain enable / disable (Switch on a Domain row).
2. FX-unit reassignment (clicking a numbered unit in an FX-unit domain's expanded picker).
3. Action enable / disable (Switch on an Action row).
4. FX slot reorder (dragging a slot row by its grip, in an FX domain).
5. End of run for the outgoing deck (the dropdown in a Domain row's title row: Leave, Restore, or Home). A domain type that offers only one value shows it as plain text.
6. Channel Fader variant (the 1 / 2 switch on the Channel Fader card).

All six follow the same rule: they change the loaded fusor, they're saved as you make them, and they're still there next time you load it. There's no Save button and nothing to remember to press.

The domain Switch here is the same switch as the one on the Domains tab in the Library, on the same fusor, and it means the same thing in both places. Whichever you touch last is the one that counts; the other view updates to match. See Domains → The enable switch.

End of run works the same way, and it is the same dropdown as the one on the Library's domain card. It acts on the outgoing deck: Leave its controls where the transition put them, Restore them to where you had them before you armed, or send them Home, to the positions the controls themselves call neutral. Full rules at Domains → End of run.

Channel Fader variant is the 1 / 2 switch on the Channel Fader card, here and in the Library's Fusor detail and inline editor. It picks which of the domain's two curve variants plays, for the outgoing and incoming sides at once. Both variants' rows stay visible with their curve previews (hover or click a curve label to preview it); the selected variant is drawn blue and the other gray. The choice defaults to 1, is saved to the fusor file, and is locked during a run like the other session edits. If the save fails, the status line reads "Channel Fader didn't save", or "Channel Fader · Incoming didn't save" when one side failed. Session View never changes the selection on its own, and opening a file does not change it. Variants are authored in the Library: see Domains → Channel Fader variants.

If variant 2 has no curve on either side, its row is grayed under its default name and the switch is disabled. When variant 2 is selected while empty, the switch stays enabled so you can return to 1. An empty selected variant modulates nothing on that side.

When to use Session View

The typical flow is: load → read the intent line → scan down the stack checking pre-run notes → adjust a domain or FX unit → arm. The adjustment is saved, so the next load opens the way you left it.