From Audacity Manual

Consistency discussion (now resolved & implemented) moved from the main page

Gale:See Consistency discussion. I prefer two links, one to File and one to the anchor in File. Anyone else?

Peter 27Feb11: I did read the recent comments in the Consistency discussion before I wrote this. But I think that it may be a case of "horses for courses". In this particular instance in the little paragraph above there is already a link to the "File" menu in the first sentence for any interested reader. In the third sentence I actually want to direct the user to the actual information relevant to them at that time i.e. the import or the open. At that stage sending them back to the top of the "File" page could be confusing as they will then need to scroll down to find what they need.
But I am perfectly happy to fall into line with whatever consistency standard we finally decide on.

Gale: I think consistency is a goal because lack of it can confuse too. Your sentence "always Open the <my_project_name>.aup file from the File menu" doesn't 100% guarantee people will use "Open". It isn't really grammatical with the "Open" capitalised either. "Choose File > Open" (linked or not) should be clearer if it is used consistently. To be both consistent and flexible, how about <anchor> after the ">" always going to the anchor, but the root menu before ">" does not have to be a link (after all, in some cases it may become tedious to repeat links, so you might only want to make a menu item into a link the first time of use.
Peter 28Feb11: I have added my thoughts to the consistency discussion in the Wiki. When a final decision on the preferred form is reached I will ensure that this page conforms.
Gale 04Oct11: Thanks, Peter. Linking only to the anchor was settled on a while ago as per Consistency#Spans_and_Divs so it would be good some time to make this page conform.
- Peter 9Oct11: done - and I will keep an eye out on other pages for similar non-conformant links. Although I clearly remember us discussing this in the Wiki thread a while back I don't recall us ever settling this one way or the other, and I note that some of that discussion has been removed from the consistency page in the Wiki. I still have a preference for a single consolidated link, but if the rule is now for the compound format I will abide by that.
- Peter 9Oct11: I've now worked through all the tutorials and think I have caught all the span class menu inconsistencies contained in them.
- Gale 10Oct11: Thanks. It was a compromise that I think satisfies everyone more or less. In any case I think it's semantically wrong to have a single link that goes somewhere that doesn't match the text for the link. You can still see the discussion in the Consistency history.

Version as of 1.3.12 pre-Apr2011 when aliased files was the default import

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.

Bill: I realize this may be a low priority, but I and a few others (based on posts on the forum) would love to see a specification of the Audacity XML.

What is an Audacity project

Bill 03Mar11: Isn't the AUP file the project file? If so, shouldn't this section be titled "AUP Project Files"?
In the paragraph below it reads as if one is exporting the AU files. I think this is misleading. One exports a project, not the individual AU files.
Changed the italic and bold settings within the parentheses in the second paragraph so that the links don't look like glossary entries.

Peter 16Mar11: actually my understanding is that the AUP file should be regarded as the "project manager" for the project (Koz often refers to it that way, or similar). So to my mind the project files are the data folders and the .au and .auf files. I changed to wording on the Exporting to try to make it clearer.

Gale: 17 Mar 11: I don't like the concepts of "master" and "manager" very much. We may have an interface called "project manager" eventually for safe moving and deletion of projects. Also the page title is "Audacity Projects" but the first phrase of the intro is "Audacity project files" and doesn't deal with the _data folder at all. I think that's more important than the exact contents of the project. some of which could be moved down.

I think there is too little here that explains why you should (or shouldn't) save a project (and how to do it) and too much in too many places about the faster/safer import thing.

I also think we should explain however briefly that the same format (with temporary folder instead of _data folder for unsaved projects) is used for the autosave file from which (hopefully) the project would be recovered if you crashed.

Peter 18Mar11:

I don't like the concepts of "master" and "manager": Point taken, I will remove such references in this text. I personally still find it hard to consider the AUP file as a "project file" as to my mind it is far from being complete in itself - however I bow to common and long-term usage to maintain documentation consistency (I note the Wiki page "File management tips .." uses that nomenclature).
I think there is too little here that explains why you should (or shouldn't) save a project (and how to do it): Good catch. I will add a draft section on this based on the text from the Wiki page noted above.
I also think we should explain however briefly that the same format (with temporary folder instead of _data folder for unsaved projects) I will add some draft text for this.
... too much in too many places about the faster/safer import thing: I put this many warnings in (actually only 3) because, with the "faster" default setting, the consequences can be serious, as we have been discussing on the Crew section of the forum and on Bugzilla on Bug 26 and its related bugs. If we were to change the default to "safer" then this page could be rewritten with most (maybe all) of the red warnings disappearing and being replaced with a "friendly" blue advice panel telling the reader about "faster" and its benefits & risks.

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.

Bill 03Mar11: The AUP files also contains gain, pan and envelope information. Do we want to include that? Perhaps the fourth point above should be integrated into the paragraph below since it isn't really talking about the project structure (the files and folder that make up the project), but instead the contents of the AUP file.

Peter 16Mar11: I don't really want to move the fourth point down - but I did add the extra text on "gain, pan and envelope information" to the paragraph below

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.

Gale:See Consistency discussion. I prefer two links, one to File and one to the anchor in File. Anyone else?

Peter 27Feb11: I did read the recent comments in the Consistency discussion before I wrote this. But I think that it may be a case of "horses for courses". In this particular instance in the little paragraph above there is already a link to the "File" menu in the first sentence for any interested reader. In the third sentence I actually want to direct the user to the actual information relevant to them at that time i.e. the import or the open. At that stage sending them back to the top of the "File" page could be confusing as they will then need to scroll down to find what they need.
But I am perfectly happy to fall into line with whatever consistency standard we finally decide on.

Gale: I think consistency is a goal because lack of it can confuse too. Your sentence "always Open the <my_project_name>.aup file from the File menu" doesn't 100% guarantee people will use "Open". It isn't really grammatical with the "Open" capitalised either. "Choose File > Open" (linked or not) should be clearer if it is used consistently. To be both consistent and flexible, how about <anchor> after the ">" always going to the anchor, but the root menu before ">" does not have to be a link (after all, in some cases it may become tedious to repeat links, so you might only want to make a menu item into a link the first time of use.
Peter 28Feb11: I have added my thoughts to the consistency discussion in the Wiki. When a final decision on the preferred form is reached I will ensure that this page conforms.

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

Peter 27Feb11: I am still not sure whether this section on moving Audacity projects really belongs on this page - or if it deserves a page of its own, linked to from this "Audacity Projects" page. Any comments?

Ed 27Feb11 Have not looked at how "long" the page is without editornote divs but unless really too long I would keep it here. Especially considering "complex structure as described above" which would have to change to a page referal

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.

Bill 03Mar11: I find the alert div below confusing. I had to read it twice to realize you were talking about importing the WAV into the new project. I think we should lose this alert or make it clearer.

Peter 16Mar11: I've tried to make it a bit clearer - any better for you Bill?

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.

Ed 27Feb11 there are other tools besides Zip, maybe a more generic description is in order?

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.

Bill 24Feb11: Sorry, Peter, but external files have absolute references in the AUP file, e.g. on Mac aliasfile="/Volumes/Disc/Path/To/ImportedFile.aiff". Thus it is impossible to move an Audacity project that depends on external files to another computer but easy to move a project to a different location on the same computer.

Gale: Not "impossible" at all on the same OS, just put the _data folder in the correct path! Please see Sending your work to others in case you want to link or there is something else you want to say here.

Bill 24Feb11: Yes, impossible unless you first copy the aliased files into the project. That appears to be what the wiki article is implying.

Gale: The Wiki doesn't say it's "impossible" (rather, it says "you must" copy in if you want to move the project to another computer). The problem is you can't say "impossible" unless it is really is :=)
If you did not copy the files in, then as well as putting the _data folder in the correct path, copy the external files to the other computer, creating a new folder if needs be to put them in the path stated in the .aup file. And even if I have your Volumes/Disc/Path/To/ImportedFile.aiff that I want to move from Mac to Win, I can just put that AIFF in an appropriate folder on Win, and do a find and replace on the aup file. I would not recommend that here, but it works.

Peter 24Feb11: I pruned the "4-byte FP" stuff from the .au file description - it is largely irrelevant technobabble to most users. The original text is parked here: The .au files are a lossless, uncompressed format using 4 byte floating point numbers.

Gale added a note: The summary files have the same format as the audio files, but there are fewer of them. Gale: Importing the same WAV aliased in one project and not so in another produces the same number of .auf files in the aliased project as .au files in the other project (at default blocksize)

Peter: Gale I'm not sure I really understand this comment - or if we need to retain it on this page?

Bill 24Feb11: I don't think we need to talk about .auf files. That's getting way too technical. FWIW, here is my understanding of .au files versus .auf files.
- AU files contain uncompressed mono audio data, and are limited to 1 MB in size. So the amount of audio they contain is dependent on the project bit depth and sample rate. Note that AU files have the same format as the project. If it is a 16-bit PCM project the AU files will contain 16-bit PCM data.
- Each AU file has a header that appears to contain the information for drawing the waveform. Gale cannot reproduce this on Windows, but on Mac if I import an Audacity .au file into a project I get 12,346 samples (at 16-bit depth, 44100 Hz) of garbage at the start of each file. That corresponds to the offset field in the header of the AU file of 24,716 bytes. AUF files contain only the waveform-drawing header information. This is why the waveform can still be drawn when the aliased (external) file is no longer available.
- Each AUF files points to a chunk of the aliased file that corresponds to exactly the same chunk of audio that would be contained in an AU file if the external file were copied in instead of aliased. Thus you always get exactly the same number of AUF files as AU files.
- I have yet to see any of these mythical "summary" files (as opposed to AUF files), either in the _data folder or referenced in an AUP file.
- I also find it peculiar that we are left to infer all this, when a developer who understands the Audacity project format could give us a definitive answer. This is akin to the debate on whether or not Audacity does all internal processing at 32-bit, which AFAICT has not been resolved either.
  - Gale: As soon as I get full time I will try and do some research and go through this article properly. I wish I had had time to do so before, but if you were unsure about doing it yourselves, you could have asked me to prioritise merging the page. It was kind of Peter to volunteer, but it might have saved time. I have raised some disquiet about the content here in a [Manual] thread which James was Cc'd on, though he did not comment. I will ping him if I am still not happy, so we get this page sorted. All that said, I still think (without rewriting it from scratch), all "heavy" technical stuff should either be tucked away at the bottom as a technical appendix, or go to Wiki.
    As for "all internal processing at 32-bit", it was never a definitive answer but Martyn said he thought so, and it does look like it. It's just not what I understood from correspondence I had ages ago with Dominic (and I still don't think I misunderstood it).
Peter 27Feb11: Gale, I rewrote this page and extended it as we keep getting posters on the forum who need to understand some of the intricacies of the Audacity project structure and also to understand the implications of the faster/safer import settings. It is much easier to develop a reasonable page here in the manual to point them at rather than rewriting it fresh each time on the forum postings. I shall not be unhappy if you should wish to rewrite/restructure this page at any stage in the future following your proposed research - and I will gladly help you with editorial reviews if you do.
Gale: I appreciate your work here, Peter. However for those on 1.2 it would be much more appropriate to send them to the existing Wiki documentation than here.
Peter 28Feb11: Thanks Gale. Yes, I agree that this page is being written for the benefit of 1.3 users (and future 2.0 users hopefully). I note from the forum that we seem to get as many, if not more, 1.3 posters these days than 1.2 (possibly helped by the retitling we did on the forum and the main Audacity site). I was aware of the File Management Tips in the Wiki, but for most readers it is far too long and far too dense - probably leading to TLDR. One of the key discussions highlighted in this rewritten Manual page is to help the reader understand the implications of "faster" versus "safer"; in the Wiki article this information is fairly well "hidden" in the dense text.

Older Version

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

AUP files and project files

Audacity project files store information about the tracks, labels and other project data. They are stored as multiple files: an AUP master file and numerous small AU audio files in subfolders. To get usable audio files in standard formats like WAV or MP3, you must Export them from the project because you can't use AUP for this. Audacity may increase processing speed, and save some space, by referencing external audio files (see Dependencies) rather than making a copy . 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! In addition, "summary information" is stored which enables the display to be redrawn rapidly.

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

a top level master project file called <my_project_name>.aup
a folder at the same filing level called <my_project_name>_data
and within the data folder, a sub-folder structure with lots of little .au files - segments of the recording (mainly audio clips - but also some housekeeping files).

JC: Between these double lines is a big section, much of it from the old manual, that probably isn't needed any more.

The date today is 25/Nov/2009. If anyone wants to rescue stuff from this section onto the main page (or elsewhere into the manual) they certainly should do so before 25/Nov/2010. It might be deleted long before then!

Outline

Old Text (to be Cannibalized)

This section was lifted from Audacity Project Format

Audacity projects are stored in an AUP file, which is a format that has been highly optimized for Audacity so that it can open and save projects extremely quickly. In order to achieve this speed, Audacity breaks larger audio files into several smaller pieces and stores these pieces in a directory with a similar name as the project. For example, if you name a project "chanson", then Audacity will create a project file called chanson.aup which stores the general information about your project, and it will store your audio in several files inside a directory called chanson_data. The Audacity Project format is not compatible with any other audio programs, so when you are finished working on a project and you want to be able to edit the audio in another program, select Export As... from the File Menu.

Audacity is sometimes used to open a file, make a quick change, and write it back to disk, and it is sometimes used to mix together a dozen tracks with hundreds of effects to create a song. For all of these needs, big and small, Audacity encapsulates whatever you're working on inside an Audacity project.

In Audacity, each window represents an Audacity project. A project represents one complete piece of audio, which might be a short recording, a 3-minute song, or an hour-long entire CD. It can have multiple tracks, hundreds of audio clips, labels, and more, but a single timeline. Audacity projects can be saved to disk and then loaded back later so you can continue where you left off. When you save an Audacity project, nearly everything about the window is saved: all of your tracks and editing information, for example. The only thing that is lost when you save and close the window is the history; you can no longer undo changes. (However, you can always save "snapshots" of your project at any time.)

Saving vs. Exporting

Audacity projects are saved to disk in a way that is very efficient for Audacity. While the format is open in theory, it is not intended to be used by other programs. When you want to create audio that can be opened by another program, copied to an iPod, or burned to a CD, for example, you should export the file as a standard format like WAV or MP3. See Audio File Formats for more info. However, when you export audio, you lose information about separate tracks, labels, and other Audacity-specific editing information. Only the final mixed audio is saved. So you should save an Audacity Project if you want to make changes later.

If we reinstate this text, adjust link to Audio File Formats if we don't have an appendix page for this (currently undecided)

Audacity Projects on disk

Rather than using a single file, an Audacity project is split into several files, often hundreds or thousands, each one containing about 10 seconds of audio. When you save a project called MyRecording, for example, Audacity creates two items on disk:

MyRecording.aup - the main project file
MyRecording_data - a folder containing the small audio files making up the project

Both of these items, and all of the files inside the data folder, are totally critical to the project! If you move one to another location, you must move the other. If you need to send an Audacity project to someone else, and a standard format like WAV or MP3 won't do, it's often best to create a Zip archive of the project file and data folder.

If you accidentally lose the project file or some of the data files, you will need to have Audacity recover as much of the project as possible. You will lose a lot of editing information, but often much of your recording can be salvaged. See Recovery for more information.

In most software programs you talk about Opening and Saving. Audacity can do those too. So what's up with Importing and Exporting?

A really common operation in Audacity is to combine many audio files into one. This could be for creating a mix tape, splicing together different segments from a mix tape, or reassembling a complete symphony from movements stored as four different CD tracks.

While it is possible to open each file and then copy and paste the contents into the same file, the preferred method in Audacity is to open just one project window, then import all of the different audio files into that window.

When the Import dialog is open, shift-click, control-click, or cmnd-click (Mac) to select multiple files to import at once.

You can also drag and drop files directly into Audacity's window.

Save: saves a project, in Audacity's internal format. Fast to open again later, but you can't use the Audacity project in a different program.

Export: mixes all of your audio down to a single mono or stereo track. You lose any extra information, like multiple tracks, volume edits, or labels; only the audio is saved.

Export formats

In the chapter on Digital Audio, we talked a little bit about compression. When you export audio from Audacity, you have to decide whether to export it compressed or uncompressed.

The most common uncompressed export formats are WAV (most common on Windows), AIFF (most common on Mac). Good for CD-quality audio. Good for burning onto a CD. Not good for emailing or uploading to the Internet unless it's just a few seconds worth of audio.

Audacity supports three common types of compressed audio as well: MP3, MP2, and Ogg Vorbis.

MP3 is the most common file format found on the Internet. If you're creating a song or podcast to share with others online, this is probably your best bet. If you use the 128 kbit compression setting, you're getting a factor of 10 compression.

MP2 is used in radio broadcast industry. If you're sending something to a radio station, this may be the format they expect. For anything else, there's probably no good reason to use it, because MP3 supercedes it.

Ogg Vorbis is a free alternative to MP3. Independent listening tests consistently show that an Ogg Vorbis file that's the same size as an MP3 file will sound better, or equivalently, if you have two files that sound the same, the Ogg Vorbis file will be smaller. You can find free Ogg Vorbis players for Windows, Mac OS X and Linux, and hundreds of portable digital players support it as well. However, Ogg Vorbis is still less well-known, and many portable devices like the iPod do not support it. The fact that Ogg Vorbis is great and patent-free means that Audacity comes with full Ogg Vorbis support built-in, while MP3 support must be added on separately.

There are two famous compressed audio formats that Audacity does not support. One of these is WMA, a secret format developed by Microsoft. Audacity cannot work with that format at all because Microsoft keeps its details hidden. The other is AAC, which is famous for being used by iTunes and the iPod. AAC is a public, documented format, and a future version of Audacity will probably offer full support for it - but not at the time of this writing.

Past discussion

delete if/when agreed

Not happy with the way this is shaping up. It is important we get the export/save distinction explained early on, but from a reference point of view that belongs on the File Menu page. Perhaps we need something that is more clearly a tutorial and to walk someone through opening and saving a project and importing and exporting audio? I don't know. I need to think about what is not working right here.
Outline of a possible walkthrough further down the page.

Bill: I don't think we need the walkthrough as that stuff is now covered in the tutorials. I am in favour of repeating the save/export distinction here - it is really important and anything we can do to drive that point home as soon as possible is good. Similarly I am in favour of repeating the dependencies information here. Otherwise I think this page should be simple and to-the-point. The Audacity Project Format page could exist for those who really want to know the technical details. Lose 'Audacity Projects on disk' (covered in Audacity Project Format) and 'Export Formats' (covered elsewhere).

Talk:Audacity Projects