# xtc User Manual (0.1.0 Development Build) xtc is a bounded Linux music-making prototype. Start with a copy of an important project and keep backups of its WAV media. Supported limits and unfinished areas are listed in KNOWN_LIMITATIONS.md; no production/device qualification is implied. --- ## Build or Install Follow BUILD.md and LINUX.md. Core: `make all test`; GUI: `make gui`, then `./build/xtc`. Use an existing JACK-compatible server and reconnect with F6. Connect `midi_in` to a controller, `input` to mono capture and `output` / `output_right` to left/right playback using your JACK routing application. No server, physical routing or system configuration is changed automatically. `xtc --version`, `xtc --help` and `xtc --diagnose` need no display/server. For a source install stage with `make install-gui DESTDIR="$PWD/build/stage" PREFIX=/usr`, inspect the stage, and use your normal deployment process. A user prefix is supported (for example an absolute path to your `.local` folder). `make uninstall` with the same DESTDIR/PREFIX removes only that version's known files. See LINUX.md for package extraction, dependencies and removal. Never use a release built for a different system ABI without rebuilding/testing it. --- ## Make A Short Project 1. New/Open starts in Sequencer. Add track; use F2 to name it. 2. Add MIDI clip, select it and open Piano roll (Ctrl+4). Left-click to draw notes, drag to move, drag a right edge to resize, Delete/right-click to remove. 3. Alternatively Import WAV (Ctrl+I). It creates/routes an Audio clips source; supported WAV formats and preload limits are in AUDIO_FILES.md. 4. Drag clips to arrange them and edges to trim. View/Snap sets the timeline grid; +/- zoom buttons and scrollbars navigate. Ctrl+D duplicates a clip after its end, retaining its complete source. F2 names clips; right-click offers duplicate/rename/delete. Alt+Up/Down with timeline focus reorders tracks. 5. Play/F5 starts; Pause/F7 or Stop/F8 leaves the position for resuming. Home returns to start while stopped (or stops first); click the ruler to seek. Recording uses Stop, not Pause. F9 Panic releases the instrument. 6. Mixer (Ctrl+2) offers track gain/pan/mute/solo and Gain/Pan automation lanes. Click to add points, right-click to remove. CONTROL.md explains timing and live CC7 volume, CC10 pan and CC64 sustain. 7. Save (Ctrl+S), close, reopen and continue editing. Ctrl+Z undoes and Ctrl+Shift+Z/Ctrl+Y redoes. New/Open resets history after unsaved-change handling. Modular Graph (Ctrl+3) exposes routing. Drag output to input to connect, select a wire/node and Delete to remove; cycles and invalid ports are rejected. Keep an Output route for playback. GUI changes show queued/active graph status. Graph positions are session-only; music/routing/automation are saved. Edits that prepare new plans stop playback; disk/compilation may pause the GUI, never run in audio. --- ## Record and Retain Media Choose a project folder and save the project there first. Record/Shift+F5 asks for an unused WAV path. Stop finalizes the take and inserts it. Existing destinations are protected, including a file created while recording. Undo/removing a take removes its reference, never the recorded file. Imported external files are also never deleted. WAVs inside the save folder become relative references; move the folder and media together. Save As preserves the same source media, not a copy. On write failure the GUI reports a retained path. Keep it and recover complete frames to a different, unused destination: ```sh xtc-check --recover-recording take.wav.tmp.XXXXXX recovered.wav ``` Only xtc's canonical float32 mono temporary format is salvaged. Incomplete trailing frames are omitted. The source is retained. Import/relink the recovered WAV. Missing/unreadable media is silent and reported; select the clip and use File/ Relink selected audio. See RECOVERY.md for interruption, disk-full and power-loss limits. Close/project operations are refused while recording; finish the take first. --- ## Trusted Effects and Sources File/Load LADSPA plugin lists compatible descriptor indices from the chosen `.so`. Loading executes native code. Select a documented compatible mono plugin, connect its graph ports, then use Edit/Selected plugin control. Edit/Selected plugin automation adds/removes tick-based linear or step points. Control names/ranges appear in the dialogs. Module identity/control values/lanes save with the project; module binaries and DSP history do not. The initial amp/inverter/sine set and unsupported layouts are listed in PLUGIN_HOSTING.md. Missing plugins reject GUI Open with identity/path information and preserve the saved/current documents. Restore the compatible module at that path and retry. Plugins are not sandboxed. --- ## Diagnose A Problem Run `xtc-check --diagnose` and capture the version, architecture, compiled features, GUI error text and steps to reproduce. `xtc-check --validate song.xtc` checks metadata without opening plugins/media; it does not certify playback resources. Check JACK routing, sample rate/format and xrun/process status in the GUI. After server loss/rate change stop/reconnect and retry. Keep the original project, media and retained temporary files before recovery attempts. A native plugin can crash/hang the process. There is no crash-isolation guarantee. Use the operating system's core-dump/debugger tools if available; xtc does not install signal handlers, change core limits or upload crash reports. Debugger/ core files may contain media paths and audio memory; share only what you intend. Report bugs following MAINTENANCE.md, including whether the issue reproduces without plugins. Physical listening and independent human install/usability acceptance remain pending. --- ## MIDI Composition In Piano roll, use the Notes menu for grid (including triplets), channel/pitch filters, velocity/channel, quantization, transposition and pattern repetition. Click selects a single note; Ctrl+A selects all filtered notes. Ctrl+D repeats that selection at a chosen spacing within the existing clip source. Up/Down transposes by a semitone. Commands are undoable through the main Edit menu. See [MIDI.md](MIDI.md#composition-commands) for shortcuts, timing and limits. --- ## Audio Clip Tools Select an audio clip, click the ruler at the desired cut while stopped, then choose Edit / Split clip at cursor (S with timeline focus). Ctrl+D duplicates; Delete removes the clip reference. Drag the body to move and edges to trim. Edit / Audio clip gain and fades (A) sets linear gain and fade durations in ticks. All are undoable and preserve the WAV file. Waveforms show cached raw source peaks, before gain/fades; large media can take time to load on Open/import. See [AUDIO_FILES.md](AUDIO_FILES.md#non-destructive-clip-editing) for boundary behavior, preview limits and the deferred stretch/pitch tools. --- ## Inspecting and Organizing Routing In Modular Graph, select a node or wire to inspect its routing in the feedback line. Arrows show direction; yellow no-output badges identify disconnected branches. L arranges nodes by signal flow. Select a wire and press I to insert a unity gain/bus node as one undoable edit. These commands are also in View/Edit and the graph context menu. Unwired effect inputs use external audio, as shown by “ext in”; they do not imply silence. See [ROUTING.md](ROUTING.md). The Mixer also offers Add bus and a Route choice for ordinary tracks. Select Track/Bus strips to edit their controls and automation. Master and selected strip meters show dBFS with 20 dB/s release; Reset peaks clears latched clipping. See MIXER.md for solo rules, gain staging and meter taps. File → Load LADSPA plugin offers a descriptor browser. Select a graph plugin and Edit → Selected plugin control for identity, values, ranges and Reset defaults; Apply commits, Cancel discards. Edit also offers replacement, reset and insertion of an effect on a selected wire. Graph wires determine processing order; Delete removes a selected plugin and its wires. Changes are undoable. Replacement keeps compatible audio wiring but resets plugin controls and automation. See PLUGIN_HOSTING.md for supported formats and failure behavior. Mixer Interpolation selects Linear or Hold for each point added or replaced. Audio → MIDI controller mapping lists all channel bindings; enter `channel volume_CC pan_CC sustain_CC` (channels 0..15, 128 disables, enabled CCs must be distinct, 120/123 reserved). Maps are undoable and saved. Controllers modify live sine voices; arranged track/bus/plugin automation takes precedence over its static controls and is unaffected by those MIDI bindings. See CONTROL.md. Unavailable main-menu undo/redo actions are disabled, including while recording. Piano roll has Edit/Undo/Redo shortcuts and a right-click note menu; right-click no longer immediately deletes notes. Graph right-click targets the node/wire under the pointer. Undo preserves surviving selections. Completed takes add one undo step; undo removes references and keeps WAV files. See EDITING.md for grouped commands, failure handling and keyboard/focus behavior. Project troubleshooting: `xtc-check --validate PROJECT.xtc` reports metadata errors with the expected record and syntax line. `xtc-check --inspect PROJECT.xtc` lists resolved media/module paths and plugin identities without executing plugins or starting JACK. Exit codes: 0 = valid metadata and available files, 2 = missing or unreadable references, 1 = metadata/I/O error. File availability does not certify WAV contents or plugin compatibility. See [PROJECT_FORMAT.md](PROJECT_FORMAT.md) for the compatibility and relocation policy. **File → Load plugin** supports LADSPA plus an initial Linux CLAP/VST2/VST3 effect subset. Select the actual module binary (`.clap` or `.so`, including a VST3 bundle's inner binary). Modern effects require one mono input and output, float32 and zero latency; they use default configuration. Instruments, modern parameter editing/automation, opaque state and custom editors are not implemented. Projects now save v12 and read v1–v12. See PLUGIN_HOSTING.md for the full contract and test/qualification limits. --- ## Instrument Support MIDI tracks can bind CLAP, VST2 and VST3 instruments. In the Track menu, select **Load instrument plugin** for the selected sequencer track; **Use built-in instrument** removes the binding. Assignment also selects the track for live MIDI. **Live MIDI to selected instrument** changes that target; **Live MIDI to built-in sine** restores the legacy live source. MIDI clip notes always go to their own track's instrument. Independent instances feed track gain/pan, mute/solo, bus routing and automation. Bindings/live target save in v12. Supply the actual trusted Linux binary (including the inner .so of a VST3 bundle). Supported instruments have zero audio inputs, one mono output, float32 processing, zero latency and one note/event input. Default configuration only: no custom editor, opaque state/preset restoration, modern parameter editing/automation, stereo/multichannel instruments or MIDI output. No arbitrary third-party instrument is qualified by the original ABI fixture tests. CLAP accepts MIDI or native notes; VST2 uses MIDI events; VST3 uses IEventList note events. Live CC reaches CLAP MIDI/VST2; native CLAP/VST3 have no controller mapping (including sustain). Live MIDI goes to exactly one selected target. Seeks/loops retrigger notes crossing the destination with fresh envelopes; plugin oscillator/opaque DSP state cannot be reconstructed. Panic delivers all-off (VST3 held-key note-offs); plugin release tails may remain. Processing uses preallocated 256-frame chunks and 256 incoming events per instance/chunk; overflow or processing failure silences the block and schedules reset events. The existing 32 simultaneous scheduled-note and 4096 stored-note bounds remain. Do not unload/replace modules during playback; candidate plans are prepared off the callback and old instances are reclaimed on the control thread. Missing references remain inspectable without loading; failed GUI preparation retains the current project. Save a backup for applications limited to v11 or earlier. --- ## Workspace The flat workspace puts New MIDI/audio track, WAV import and instrument loading in a persistent sidebar, with a musical transport display and selected-track overview. See [WORKSPACE.md](WORKSPACE.md) for shortcuts and workflow. Open `modern-session.xtc` in the installed examples for an original four-track arrangement. Use the sequencer Snap dropdown for straight/triplet/bar grids or Off. Double-click MIDI clips to edit notes, then use the Velocity lane or selected-note slider for dynamics. Each non-bus track header has an instrument dropdown offering built-in sine, project instruments and explicit plugin loading. See WORKSPACE.md. Additive clip selection, atomic group commands, phrase clipboard and repeat, alignment/slip tools, MIDI swing/gate/legato/scale/velocity transforms, batch audio fades and static mixer A/B recall are also available. See [MODERN_EDITING.md](MODERN_EDITING.md) for commands, scope and limitations. See [arrangement and composition workflows](COMPOSITION_WORKFLOWS.md) for markers, MIDI composition, normalization and portable media collection. Select an audio clip and open View / Sample editor (or double-click it) to inspect source samples, choose native frame ranges, trim the clip or export a new WAV. Processing and one-level local undo remain in the editor until Save full copy and relink. See [AUDIO_EDITOR.md](AUDIO_EDITOR.md) for all sample tools, transient slicing, musical-tick rounding and source preservation limits.