Understanding Basic Concepts and Terminology

In order to fully grasp the terms used in Ardour (and this manual), it is necessary to understand what things like sessions, tracks, busses, regions and so on—as used in Ardour—are.


An Ardour session is a container for an entire project. A session may contain an arbitrary number of tracks and busses consisting of audio and MIDI data, along with information on processing those tracks, a mix of levels, and everything else related to the project. A session might typically contain a song, an entire album, or a complete live recording.

Ardour sessions are kept in directories; these directories contain one or more session files, some or all of the audio and MIDI data, and a number of other state files that Ardour requires. The session file describes the structure of the session, and holds automation data and other details.

Ardour's session file is written in XML format, which is advantageous as it is somewhat human-readable and human-editable in a crisis. Sound files are stored in one of a number of optional formats, and MIDI files as SMF.

It is also possible for Ardour sessions to reference sound and MIDI files outside the session directory, to conserve disk space and avoid unnecessary copying if the data is available elsewhere on the disk.

Ardour has a single current session at all times; if Ardour is started without specifying one, it will offer to load or create one.

More details can be found in the Sessions chapter.


A track is a concept common to most DAWs, and also used in Ardour. Tracks can record audio or MIDI data to disk, and then replay it with processing. They also allow the audio or MIDI data to be edited in a variety of different ways.

In a typical pop production, one track might be used for the kick drum, another for the snare, more perhaps for the drum overheads and others for bass, guitars and vocals.

Ardour can record to any number of tracks at one time, and then play those tracks back. On playback, a track's recordings may be processed by any number of plugins, panned, and/or its level altered to achieve a suitable mix.

A track's type is really only related to the type of data that it stores on disk. It is possible, for example, to have a MIDI track with a synthesizer plugin which converts MIDI to audio. Even though the track remains MIDI (in the sense that its on-disk recordings are MIDI), its output may be audio-only.

More details can be found in the Tracks chapter.


Busses are another common concept in both DAWs and hardware mixers. They are similar in many ways to tracks; they process audio or MIDI, and can run processing plugins. The only difference is that their input is obtained from other tracks or busses, rather than from disk.

A bus might typically be used to collect together the outputs of related tracks. Consider, for example, a three track recording of a drum kit; given kick, snare and overhead tracks, it may be helpful to connect the output of each to a bus called "drums", so that the drum kit's level can be set as a unit, and processing (such as equalization or compression) can be applied to the mix of all the tracks. Such busses are also called groups.


A track may contain many segments of audio or MIDI. Ardour contains these segments in things called regions, which are self-contained snippets of audio or MIDI data. Any recording pass, for example, generates a region on each track that is enabled for recording. Regions can be subjected to many editing operations; they may be moved around, split, trimmed, copied, and so on.

More details can be found at Working With Regions.


The details of what exactly each track should play back is described by a playlist. A playlist is simply a list of regions; each track always has an active playlist, and can have other playlists which can be switched in and out as required.

More details can be found in the Playlists chapter.


Ardour allows processing audio and MIDI using any number of plugins. These are external pieces of code, commonly seen as VST plugins on Windows or AU plugins on Mac OS X. Ardour supports the following plugin standards:

LADSPA the first major plugin standard for Linux. Many LADSPA plugins are available, mostly free and open-source.
LV2 the successor to LADSPA. Lots of plugins have been ported from LADSPA to LV2, and also many new plugins written.
VST Ardour supports VST plugins that have been compiled for Linux.
AU Mac OS X versions of Ardour support AudioUnit plugins.

Ardour has some support for running Windows VST plugins on Linux, but this is rather complicated, extremely difficult for the Ardour developers to debug, and generally unreliable, as it requires running a large amount of Windows code in an emulated environment. If it is at all possible, it is strongly advisable to use native LADSPA, LV2 or Linux VST plugins on Linux, or AU on Mac OS X.

More details can be found at Working With Plugins.