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Qtractor

Qtractor is an open-source audio and multi-track sequencer application designed primarily for , functioning as a (DAW) with a for home studio use. Written in C++ and built around the framework, it enables users to record, edit, and playback multi-track audio and data, supporting integration with the for audio routing and ALSA for handling. Released under the GNU General Public License version 2 or later, Qtractor emphasizes modular support including the LADSPA, , DSSI, VST, and CLAP formats, making it suitable for music production in home studios and by open-source enthusiasts. Development of Qtractor began in April 2005 as a personal hobby project by developer Rui Nuno Capela. The first public release, version 0.1.0, occurred in January 2008. Capela has maintained sole development, with steady updates; as of October 31, 2025, the latest version is 1.5.9, still designated as . features of Qtractor include unlimited counts for audio and , real-time playback and recording capabilities, a built-in mixer with auxiliary sends, and support for time-stretching and pitch-shifting via integrated plugins. Its configuration is stored in a user-specific file at $HOME/.config/rncbc.org/Qtractor.conf, allowing customizable session management without reliance on proprietary hardware. While targeted at users, Qtractor has garnered a niche following in the open-source music community for its lightweight footprint and avoidance of resource-intensive dependencies, distinguishing it from commercial DAWs.

Development and history

Origins and development timeline

Qtractor originated as a hobby project in April 2005, developed by Rui Nuno Capela as an initial Qt3-based application focused on multi-track audio and sequencing for users. From the outset, it drew influences from the Linux audio ecosystem, incorporating early integration with the to enable low-latency audio and handling. The project's foundational release, version 0.1.0, arrived in January 2008, introducing basic multi-track support for recording and playback. Development progressed steadily, with a significant upgrade to the Qt4 framework in 2007 to enhance performance and incorporate modern UI capabilities. Further transitions followed, including adoption of Qt5 in 2016 and Qt6 in 2020, each iteration improving stability, rendering efficiency, and interface responsiveness while maintaining compatibility with evolving audio tools. Key milestones marked Qtractor's evolution, such as version 0.5.0 in 2011, which added a dedicated editor for clip-based event manipulation and notation. The software achieved its first stable release with version 1.0.0 in 2024, solidifying core functionality for professional-grade workflows. Version 0.9.27 in 2022 introduced experimental support for CLAP formats. The most recent update, version 1.5.9 released on October 31, 2025, included various bug fixes and refinements to enhance hosting and session management. Throughout its history, Qtractor has maintained an ongoing progression from to phases, with releases typically emerging in seasonal batches to incorporate and ecosystem advancements. Development remains hosted primarily on for file distribution and the GitHub repository under the rncbc organization for and collaboration.

Developer and licensing

Qtractor was developed by Rui Nuno Capela, a programmer based in near , who has created it as a solo project since its inception. Capela is also known for developing other audio tools, including QjackCtl for JACK audio server control, Qsynth as a Qt-based , and Qsampler for software sampler management, all part of his broader rncbc suite of open-source applications. As a hobbyist endeavor, Qtractor's creation was motivated by Capela's personal interest in providing accessible audio production tools for home studio users within the audio , filling gaps in native sequencing software for the platform. The software is licensed under the GNU General Public License (GPL) version 2 or later, a model adopted from the 's start in 2005 that guarantees users the freedom to freely redistribute, modify, and access the source code. This open-source licensing aligns with the principles upheld by the audio ecosystem, promoting transparency and -driven improvements. Qtractor is distributed primarily through its official page on , where source tarballs and binary packages are available for major distributions, facilitating easy installation and updates for users. While development remains largely under Capela's direction as a single-maintainer , involvement is limited but actively encouraged via issue tracking and patch submissions on the 's repository.

Technical foundation

Architecture and technologies

Qtractor is implemented in C++ to ensure high performance in handling real-time audio and MIDI processing. The application leverages the Qt framework, specifically Qt6 (version 6.1 or later), for its cross-platform graphical user interface and event handling capabilities. The software employs a non-destructive editing model, where audio and MIDI data are referenced through clips rather than being directly altered on disk, preserving original files throughout the editing process. This approach is complemented by an unlimited undo/redo system, managed via command stacks that track session, track, and clip modifications for reversible operations. At the backend, Qtractor integrates with the for real-time audio routing and low-latency processing, enabling precise synchronization and transport control across connected applications. For MIDI input and output, it utilizes the sequencer, which handles event queuing and playback in one-second periods aligned to the JACK transport. Sessions are saved in the .qtr (or .qts for snapshots), an XML-based structure that encapsulates tracks, clips, data, and plugin states, allowing for readable and portable project files. Audio handling supports multiple sample rates, such as 44.1 kHz and 48 kHz, and bit depths ranging from 16-bit integer to 32-bit floating-point, facilitated by the libsndfile library for reading and writing various file formats without quality loss. MIDI processing occurs through internal event buffers that queue and manage events for efficient playback and recording, with support for import and export in Standard MIDI File (SMF) formats 0 and 1.

User interface and workflow

Qtractor's graphical user interface (GUI) is designed to follow the conventions of modern digital audio workstations, providing an intuitive layout for multi-track audio and MIDI sequencing. The main window is divided into several key components: the track view occupies the left pane, displaying vertical lanes for audio and MIDI tracks with controls for properties such as volume, panning, and mute/solo states; the central area features the timeline with clip arrangements; the bottom pane houses the clip editor for detailed inspection and manipulation of selected audio waveforms or MIDI piano rolls; and the mixer panel, accessible as a separate dockable window (via F9 or View > Windows > ), includes track strips for adjusting volume, pan, EQ, and effects routing. Transport controls, located near the central clock display, manage playback, recording, and looping functions, with a red playhead line indicating the current position on the timeline. Typical workflows in Qtractor begin with creating a new session through > New, followed by saving it as a .qtr file (Ctrl+S) to set properties like and . Users then add via > Add Track, selecting audio or MIDI types, and configure inputs using the Connections window (F8) for JACK audio/ routing. Arming a track for recording involves clicking the button in the track header or using shortcuts like Shift+, while monitoring input levels occurs in the mixer panel to ensure proper gain staging before pressing the Record button in the transport controls. Sessions can be exported as mixed audio or individual tracks through > Export , routing output via the JACK master bus for integration with other system applications. Efficiency is enhanced by customizable shortcuts, accessible via Help > Shortcuts, with defaults including Space for play/stop, Ctrl+N for new session, Ctrl+S for save, and numeric keys (1-9) for selecting the first nine tracks. Record arming can be set to Ctrl+R or similar via the editor, allowing users to tailor bindings to their preferences while avoiding conflicts with shifted non-alphanumeric keys. The interface supports customization through dockable panels for components like the files browser, tracks list, and , which can be rearranged or floated as needed. Theme support leverages styles for visual adjustments, configurable in > Options, enabling light/dark modes or custom color schemes for tracks and clips. Snapshot saving allows users to store session variants by saving as separate .qtr or .qts files, preserving different arrangements without overwriting the original. Qtractor emphasizes with a clip-based system, where audio and MIDI clips can be dragged and dropped onto the for flexible positioning, overlapping, and reordering, supporting creative workflows like takes or rearranging sections without destructive changes.

Core features

Sequencing and recording

Qtractor supports an unlimited number of audio and tracks within a session, constrained only by system resources, enabling complex multi-track arrangements. Tracks can be grouped and routed through buses for efficient signal management, such as assigning multiple tracks to a dedicated drum bus for collective processing. The software provides versatile recording modes, including direct monitoring for low-latency input, punch-in/out for precise corrections, and overdub for layering new material over existing tracks. It facilitates simultaneous multi-channel recording, limited by the underlying audio system's capabilities, such as those provided by JACK. Qtractor's playback engine incorporates tempo mapping, permitting multiple tempo changes throughout a session via the Tempo Map/Markers window, alongside adjustable time signatures to accommodate dynamic compositions. The transport controls, accessible in the , manage playback, looping, and during sequencing. A configurable is integrated to aid recording and playback synchronization, offering audio-based options using sample files for bars and beats or a click track routed through external devices. Users can set the pre-roll count in session options to provide lead-in counts before recording or playback begins. Session management allows saving and loading projects in .qtr format, with snapshots (.qts) for versioning different arrangements without overwriting the original. Export capabilities include rendering sessions to , , OGG, or broadcast (BWF) formats, supporting ranges from full sessions to selected clips. For MIDI sequencing, Qtractor enables note velocity editing in the piano-roll editor's value grid, where velocities are visualized as adjustable bars or ramps for expressive control. Controller automation supports parameters like and pitch bend, drawn as curves with nodes for linear or . Program changes are handled through the Instruments window, utilizing .ins or .midnam files to select patches on external synthesizers or soft synths.

Editing tools

Qtractor provides a dedicated audio clip editor for manipulating recorded or imported audio material non-destructively. The editor features waveform visualization, displaying approximate waveforms with peak and RMS envelopes to facilitate precise identification of audio content and transients. Users can apply fade in/out curves directly on clips by dragging semi-transparent nodes at the edges, supporting linear, quadratic, or cubic interpolation for smooth transitions. Time stretching is available, allowing adjustments from 10% to 1000% of the original duration using a custom WSOLA-like algorithm derived from the SoundTouch library; since version 1.5.3, optional support for the Rubber Band Library (librubberband) provides advanced options including formant preservation. Pitch shifting supports shifts of up to ±40 semitones; these operations do not include formant preservation by default. For MIDI editing, Qtractor offers multiple views within the MIDI clip editor to handle note and event data. The piano roll view presents notes as rectangles on a grid, enabling graphical editing of , timing, , and duration, with tools for quantization, , and time-shifting. An event list, referred to as the Value Grid, allows precise textual adjustments to parameters like , bends, and controllers, with customizable columns for focused workflows. While a dedicated mode is not explicitly separated, the piano roll supports percussion patterns through note-specific editing on drum channels, accommodating grid-based input for rhythmic sequences. Automation in Qtractor is managed via per-track lanes, where users can draw curves for parameters including , , mute/solo states, and individual controls. These lanes utilize node-based editing, with Bézier curves in spline mode for creating smooth, natural transitions between automation points; logarithmic options adjust curve degrees based on node differences for proportional changes. data is stored non-destructively, allowing playback and adjustment during mixing. Clip manipulation tools enable non-destructive editing of both audio and MIDI clips directly in the timeline. Cuts and splices are performed by splitting clips at the playhead or selection boundaries using the Clip > Edit > Split command, preserving the original files while creating new segments. Reverses can be applied during merge or export operations to play audio backward without altering source files. Looping is supported by setting loop points via Transport > Loop Set or using Paste Repeat for repetitive sections, with crossfades automatically generated between overlapping clips or manually adjusted via fade tools to avoid clicks. Qtractor supports import and export of clips in standard formats to integrate with external workflows. Audio clips can be imported from and exported to WAV, AIFF, OGG Vorbis, and FLAC files, leveraging libsndfile for broad compatibility. MIDI clips handle Standard MIDI Files (SMF) in formats 0 and 1 for seamless transfer of sequence data.

Plugin and integration support

Supported plugin formats

Qtractor provides native support for several audio plugin formats, enabling users to integrate effects, instruments, and processors into tracks and buses for multitrack sequencing and mixing. The supported formats include LADSPA for basic audio effects, DSSI for instrument plugins with graphical interfaces, LV2 as a versatile standard for both effects and instruments, native Linux VST2 and VST3 plugins, and the modern CLAP format. These formats allow for unlimited plugins per track or bus, with features such as preset management, parameter automation, and GUI embedding. LADSPA (Linux Audio Developer's Simple Plugin ) offers a lightweight architecture primarily for audio effects and filters, without native support for processing or graphical user interfaces in most implementations. Qtractor scans and loads LADSPA plugins during startup, allowing insertion via drag-and-drop onto audio or tracks for real-time processing. While simple and efficient, LADSPA plugins lack advanced features like presets or automation curves compared to newer formats. DSSI (Disposable Soft Synth Interface) extends LADSPA by supporting MIDI-compatible instrument plugins, including soft synthesizers with elements for parameter control. In Qtractor, DSSI plugins can receive input from tracks and route audio output to the mixer, facilitating virtual instrument integration. This format also enables Windows VST plugins through wrappers like dssi-vst, which utilize Wine for , though may require bridging to isolate crashes. Preset saving and basic parameter adjustments are supported, but DSSI is considered legacy for complex workflows. LV2 (LADSPA Version 2) serves as an extensible successor to LADSPA, providing full support for both audio effects and instruments, including rich hosting, preset management, and parameter . Qtractor hosts plugins with complete routing, surround sound capabilities in compatible implementations, and curves for dynamic control during playback or recording. Plugin parameters can be automated via the track editor, and GUIs are embedded using X11 forwarding, though minor latency may occur. This format is central to Qtractor's plugin ecosystem due to its balance of features and open standards. Native VST (Virtual Studio Technology) support in Qtractor covers Linux-compiled VST2 and VST3 plugins for effects and instruments, with direct loading without external dependencies. For Windows VST plugins, compatibility is achieved via Wine-based wrappers integrated through DSSI or similar bridges, enhancing by sandboxing potentially unstable plugins. VST plugins benefit from Qtractor's preset and chunk , allowing program changes and , but the relies on third-party ports for broader availability. GUI forwarding is handled similarly to , with X11 embedding for interactive control. CLAP (CLever Audio Plugin) format was added to Qtractor starting with version 0.9.27 in 2022, offering modern features like advanced automation, per-note expressions, and native support for immersive audio production. It accommodates both effects and instruments with robust handling and preset management, scanned alongside other formats on application launch. CLAP plugins integrate seamlessly into chains, supporting parameter curves and embedding, positioning it as a forward-looking option for high-performance workflows. As of version 1.5.9 (October 2025), CLAP support remains included. Plugin management in Qtractor involves automatic scanning and discovery at startup from designated directories, enabling quick insertion via the window or drag-and-drop onto tracks and buses. Users can create plugin chains for serial processing, save custom presets, and automate parameters through editable curves linked to events. While integrates with the broader tools, limitations include reliance on bridges for non-native formats like Windows VST, potentially introducing or . Native VST3 plugins are directly supported without wrappers.

External software integration

Qtractor facilitates seamless integration with other audio applications through the , which serves as a central patchbay for routing audio and data between Qtractor and external software. This enables users to connect Qtractor's output ports to applications like Ardour for mastering or Carla for advanced plugin hosting and processing, allowing complex workflows where Qtractor handles sequencing while external tools manage specialized tasks. For MIDI connectivity, Qtractor leverages ALSA sequencer ports to interface with hardware controllers and software synthesizers, such as for sample-based sound generation. This setup allows direct MIDI input from controllers to Qtractor's tracks or routing to external synths, supporting real-time and playback without requiring additional intermediaries. Qtractor is compatible with via its JACK emulation, functioning as a for JACK on contemporary distributions as of 1.5.9 (October 2025), which simplifies audio management and enhances low-latency in modern desktop environments. Qtractor's session templates provide a foundation for integrating tools like for drum pattern generation or for beat and loop exports, by preconfiguring audio and buses that route external outputs into Qtractor's mixer via JACK connections. Users can save these templates to streamline recurring setups, such as channeling 's per-instrument outputs to individual Qtractor tracks for mixing. Interoperability is further supported through export and import capabilities, including STEM exports of individual tracks for collaborative editing and standard formats like and AIFF for compatibility with professional tools such as . These exports preserve audio fidelity using libsndfile, enabling seamless transfer of multitrack sessions across different applications. Automation of external parameters, such as volume or effects in connected JACK clients, can be achieved through Qtractor's support for JACK control protocols, allowing dynamic adjustments during playback or recording sessions.

Compatibility and requirements

Platform support

Qtractor is designed exclusively for operating systems, serving as its primary and officially supported platform. It integrates seamlessly with the Linux audio ecosystem, including the (JACK) for audio and the (ALSA) for . The application is available in the official repositories of major distributions, such as , , , , and , facilitating easy installation via package managers like apt, dnf, , and zypper. There are no official ports or builds for Windows or macOS, as Qtractor relies on Linux-specific audio infrastructure that is not natively available on those systems. Attempts to run it on non-Linux platforms, such as through compatibility layers like Wine, result in limited or non-functional operation due to these dependencies. On the side, Qtractor primarily targets x86_64 architectures but also supports -based systems through community-maintained builds, including for devices like the . These builds have been available in distributions such as since at least version 0.9.x around 2018, enabling use on low-power embedded platforms. A soundcard with multiple inputs is recommended for , alongside USB controllers for input. For optimal low-latency performance, particularly in audio processing, a kernel is recommended, especially on older kernels prior to version 2.6.38.4; however, Qtractor operates adequately on standard kernels from 2.6.38.4 onward, with patches available for enhanced responsiveness. The benefits from 's high-DPI scaling capabilities, with effective support introduced for 5.6 and improved in subsequent versions, including 6, allowing scalability on modern high-resolution displays without manual adjustments.

System dependencies

Qtractor relies on several core software libraries to function, providing its , audio and handling, and file capabilities. The primary dependencies include the Qt6 libraries for the framework, libjack for real-time audio processing and routing, libasound for sequencing via the ALSA subsystem, libsndfile for audio file reading and writing, and librubberband for time-stretching and pitch-shifting operations. Optional dependencies enhance specific features, such as liblo for (OSC) remote control, liblrdf for discovering LADSPA plugins through RDF descriptions, Wine for hosting Windows VST plugins. To compile Qtractor from source, build dependencies are required, including a like g++, version 3.15 or higher, , and development headers for the core libraries such as qt6-base-dev, libjack-dev, libasound2-dev, libsndfile-dev, and librubberband-dev. Additional build packages cover plugin support, including ladspa-sdk for LADSPA, dssi-dev for DSSI, lv2-dev with for , and liblo-dev. At runtime, Qtractor requires a running JACK audio server (such as ) for low-latency audio and connections, with ALSA handling underlying operations. Since version 0.9.7 in 2021, has been supported as an alternative to JACK through pipewire-jack, addressing compatibility issues in modern distributions. Tools like QjackCtl are recommended for managing the JACK server.

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