Import / Export Preferences
From Audacity Manual

MP3 Export Library
- MP3 Export Library Version: This shows the current version of the LAME MP3 encoding library being used by Audacity for MP3 export. If a suitable version of LAME is not accessible to Audacity, the message will instead state that the library is "not found". In that case, use the provided buttons to either locate LAME on your computer or download a free copy of it, following the instructions on the LAME MP3 page.
- Find Library: If you already have the LAME library on disk and Audacity can't find it, use this button to tell Audacity where it is.
- Download: Use this to fetch a copy of the LAME library.
- Quality settings for all exported file formats: Users of the previous stable 1.2.x Audacity will recall that bit rate and bit depth for exported files were set on this Preferences tab (which was then called "File Formats"). However, in Audacity 1.4 you now choose export settings for the various formats at the time of export by clicking Options in the File Export Dialog. This saves the separate step of going into Preferences each time you want to to change export settings.
When importing audio files
Audacity always makes a copy of compressed files like MP3, OGG and FLAC when it imports them. The data is copied either into the temporary folder, or into the _data folder of an open project. Uncompressed files (WAV or AIFF) are very much larger, so may lead to a shortage of disc space if copied in. Audacity therefore allows you to choose from the following two options when importing WAV or AIFF files:
- Make a copy of uncompressed audio files before editing...: This is the safest (and default) option, meaning that Audacity will always have its own copy of imported files to work with. Also choose this option if you need to open your Audacity .aup project file on another computer, or send it to someone else. Note: you don't need to choose this option if you are sending an exported audio file like an MP3 to someone else.
- Read uncompressed audio files directly from the original...: Import of the audio will be faster, but Audacity will depend on the file remaining accessible and having the same name and location as when you imported it. If the file is inaccessible, the waveform will have no audio.
In development builds of Audacity, checking the above option enables On-Demand Loading of uncompressed files.
- Normalize all tracks in project: The imported file (in any format) and all audio tracks already on screen will be normalized to your current setting for the normalize effect.
When saving a project that depends on other audio...
This option allows you to choose what happens if you are reading directly from an uncompressed file and then attempt to save an Audacity project.
- Always copy all audio into project: Any dependency on external audio files will be automatically removed. As soon as the project is saved, you can safely move, rename or delete any audio files that were opened or imported.
- Do not copy any audio: The project will be saved automatically but will depend on any opened or imported files remaining accessible and having the same name and location as before.
- Ask User: Whenever you attempt to save a project that depends on other audio files, you will be offered the option to copy the dependent audio files in to the project, or not.
You can check at any time if your work depends on other files, and copy the files in if you need to, by clicking
When exporting tracks to an audio file
- Always mix all tracks down...: This is Audacity's default behavior and means that if your project contains only mono tracks panned to center, they will be mixed upon export to a file containing a single mono channel. The audio will still play equally out of both speakers on most systems. If you have any stereo tracks in your project (or any mono tracks panned away from center), the exported file will be stereo, containing two channels (left and right).
- Use custom mix: When this option is enabled, an Advanced Mixing Options window appears immediately after the completing the File Export Dialog. Advanced Mixing gives you much greater flexibility in mapping your audio tracks to specific output channels in the exported file. In particular it allows export of multichannel files (that is, having more than two channels of audio) in WAV, AIFF, OGG and FLAC formats.
- Show Metadata Editor prior to export step: By default, the Metadata Editor pops up every time you export a file with the or commands. Uncheck this option if you don't want to add embedded information tags to your files.