Audacity Projects

From Audacity Manual

Audacity project files store information about the entirety of the project such as the number of tracks and their time positions, details of clips within the tracks, amplitude envelope points, labels and gain and pan data.

What is an Audacity project

Audacity project files store information about tracks, labels and other project data. An Audacity project consists of the AUP project file and its associated _data folder which contains numerous small AU audio files in subfolders. An Audacity project cannot be played in a media player such as Windows Media Player or iTunes. To obtain playable audio files it is necessary to Export the Audacity project to WAV files, MP3 files or similar.

Audacity may increase processing speed, and save some space, by referencing external audio files rather than making a copy (this will depend on the settings that you have in your Preferences for Import/Export, see Dependencies below). Note carefully that your project will no longer work if you rename, move, delete or overwrite the original audio file(s) on which it depends.

Audacity projects contain audio clips arranged onto tracks. The project's structure is:

A project file - the name of the project followed by ".aup", for example "my_song.aup"
A _data folder with the same project name and in the same folder as the AUP file, for example "my_song_data"
Within that _data folder, a sub-folder structure with lots of little AU files which are segments of the recording
Additionally data is stored which enables Audacity to manage the graphical waveform display and carry the links to any external dependent audio files in use by the project.

The project file describes how Audacity links these AU files together to make up the clips and tracks in the project; it also contains gain, pan and envelope information. The AUP file is in XML format and can be opened in a text editor if required. The AU files are stored in a lossless, uncompressed format. Their default size is 1 MB or less. This Audacity Project Format is designed to make editing audio faster in Audacity. By updating individual AU files during editing, Audacity can change audio or move audio around in the project without copying large quantities of data from one place to another.

Audacity's project format is not compatible with any other audio program. When you Save an Audacity project, it is saved in the Audacity Project Format ; an AUP file cannot be played using an MP3 player.

The four rules for keeping your Audacity Project happy:

When importing an uncompressed audio file with the "Read uncompressed file directly from the original (faster)" option checked in Import / Export Preferences (and note this is the Audacity default setting), never move, rename or delete that file, unless you first copy it into the Audacity project. See File > Check Dependencies for more information.
Never move, delete or rename any of the files or folders inside the _data folder.
Never rename the AUP file or the _data folder.

Always keep the AUP file and the _data folder together in the same directory (folder).

Opening an Audacity project

When opening an Audacity project always use the File > Open command to open the <my_project_name>.aup. Do not attempt to open, import or manipulate any individual AU files.

Audio for use in Audacity, but which was not recorded in Audacity, will need to be imported using File > Import or File > Open. The Import command is used to import audio data into an already open project, whereas the Open command used on an external audio file will either open a new Audacity project, and import the audio data into it, if the current project already contains any tracks; or import the audio data into the current project if contains no tracks.

Dependencies

Depending on the Import/Export Preferences settings, when an uncompressed audio file such as WAV or AIFF is imported or opened, Audacity may save time by not making a copy of the file and in that case will refer externally to the original file as it manipulates the audio data within the project (while not ever making any changes to that audio file unless it is told to do so).

This external reference is the default (faster) setting for Audacity's Preferences.

Be very careful not to modify such audio files with another program (or move, re-name or delete them) while they are open in Audacity.

When a project is saved, providing that Audacity's default setting has not been changed in the project's Preferences settings, Audacity will display a dialog box showing these dependencies and give the option of copying all of the audio data into the project making it independent of external audio files and making it safe to delete, move or modify the original audio files if necessary. The project's Preferences settings can be modified so that Audacity will not ask but will always either "never copy" the dependent audio files, or "always copy" them into the project on exit from Audacity.

At any time it is possible to click on File > Check Dependencies... to see if the project depends on any external files.

Import settings: "faster" versus "safer"

There are two settings available to control the manner in which the File > Import command operates. The default setting is Read uncompressed audio files directly from the original (faster) and the other is Make a copy of uncompressed audio files before editing (safer).

The faster option: This is the default option and is set this way as the default so that Audacity can use its On-Demand Loading to operate faster and save disk space. Import of the audio will usually be faster, but Audacity will depend on the audio file remaining accessible and having the same name and location as when you imported it. The audio file is not actually imported or copied into the project in this case, rather it is accessed as an external file by Audacity.

The safer option: This is the more secure option to choose, meaning that Audacity will always have its own copy of imported files to work with. Choose this option if the Audacity project file is required to be opened on another computer, or to be sent to someone else. This option need not be chosen if an exported audio file like an MP3 or WAV file is to be sent to someone else.

It is important to understand the implications of the default setting as faster . If this is left to the default value then it is crucial that any uncompressed audio file on which your project depends is not moved, deleted or renamed. If this happens then although the project will still show the correct blue waveform in the display, there will be gaps in the project's sound as Audacity will be unable to find the external audio file(s) on which the project depends.

If plenty of disk space is available and the time taken to make the full import is not an issue, then it is strongly recommended that this Preference be set to the safer option. This way the project will then always remain independent of external audio files.

Saving an Audacity Project

Saving an Audacity project lets you save unfinished work and re-open it later in Audacity exactly as it was, with all edits and recorded/imported tracks preserved. When saving an Audacity project always use the File > Save Project or the File > Save Project As... command to open the <my_project_name>.aup.

There is no need to save a project, unless required, as it is possible to work with temporary project files and then just Export the required audio files. If the project is not saved, the necessary audio data is stored in the temporary folder specified in the Directories section of Preferences until exiting the program. At that point, Audacity offers the choice of saving a project or not.

The temporary folder uses the same format as the _data folder that you get when you Save a project. In addition to being the working folder for an un-saved project, the temporary folder is also used for the autosave file from which the project can be automatically recovered if your computer crashed while recording or editing an Audacity project.

Some benefits of saving a project:

No need to re-import or re-record files
Fast loading, even of multiple long tracks
Audio data always preserved in lossless quality. This is useful if you have already exported to a lossy audio format like MP3 but decide to edit the project further. Editing and re-exporting the project saves the additional quality loss of re-editing the previously exported MP3.

Exporting Audio

Neither the .aup project file or the .au files in the _data folder can be used in other programs or devices. To use the project's audio outside Audacity, choose File > Export... which brings you to the File Export Dialog. Here you can choose from various standard audio file formats according to your purpose. The two most common formats which can be played almost anywhere are

WAV: a lossless format giving perfect quality, ideal for burning to Audio CDs
MP3: a lossy format, but small enough to send over the internet or store on portable devices.

To export as MP3, don't forget to add the LAME MP3 library to your computer. Add the FFmpeg library to your computer to export to AAC or WMA which are used in iTunes and Windows Media Player respectively.

How to move an Audacity Project

Moving Audacity projects can be tricky due to their complex structure as described above. Any project can be moved on the same computer by making a copy of the project with the Save Project As... command.

Simple Projects

For a simple single track project (that does not have gain or pan settings, or use an envelope to adjust the volume) one possible solution is to not to move the project. Instead, use the File > Export command to export a WAV file. This WAV file can then be copied to another computer, then the File > Import command can be used to load the WAV file into an Audacity project. Alternatively the WAV file can be sent by e-mail or via a file sharing web site to someone else who can import it into an Audacity project on their computer.

Unless the Audacity default Preferences setting for Import has been changed to the "Safer" mode Audacity will not actually copy the WAV file into the project when you use the Import command but will instead reference it as an external audio file.

Complex Projects

For a project that has multiple tracks, or a single-track project that has gain or pan settings or uses an envelope to adjust the volume of the track, the entire project will need to be moved. To do that it is necessary to move the AUP file <my_project_name>.AUP and the _data folder <my_project_name>_data either to a second computer or to a different location on the existing computer. Ensure that the .aup file and _data folder remain together in the same folder.

As noted above, any project can be moved to a different location on the same computer using the Save Project As... command.

If you want to move a project to a different computer the project must not depend on external audio files. Use the File > Check Dependencies... command to check whether the project depends on any external files. If it does, the dialog box will give you the option to make a copy of those files within the project.

It can be difficult to e-mail complex projects to other users; to do so it is necessary to zip up the entire project structure and e-mail or share that zip file. The reason for zipping up the project is to make sure the project structure remains intact during the transfer, not to save space. A zip archive of a project is likely to be about 10% smaller than the unzipped project.

External files have absolute references in the AUP file and thus it is difficult to move an Audacity project that depends on external files to another computer but relatively easy to move a project to a different location on the same computer. See this article in the Wiki on Sending your work to others.