Audacity 101: File formats and the power of the undo
Audacity will open a variety of file formats:
• WAV (A Microsoft format often erroneously thought to stand for Windows Audio-Video – in fact it stands for Waveform Audio File Format)
• AIFF (Audio Interchange File Format, primarily an Apple codec [coder-decoder])
• MP3 (Motion Picture Experts Group MPEG-1 layer 3)
• Ogg Vorbis (an open-source alternative to MP3)
• FLAC (Free Lossless Audio Codec)
• MP2 (a smaller lossier version of MP3)
Once a file is opened you can save it as (using “export”) any of the other formats, even if it’s not the format you opened it in.
Each of these formats has different resolutions you can use:
• WAV (sample rate 8k to 384k, bit depth 8 to 32 bits)
• AIFF (same options as WAV)
• MP3 (8k to 48k, 145 to 320 kbps)
• Ogg Vorbis (8k to 384k, “quality” 1 to 10)
• FLAC (8k to 384k, 16 or 24 bit)
• MP2 (32k to 48k, MPEG1 or MPEG2, bit rate 32 to 384 kbps)
Of course, saving in a higher resolution does not add any content. It just spreads out what you have over more samples.
Codecs are classified as either “lossless” or “lossy,” and some people claim to be able to hear the difference (my ears don’t hear it, using standard resolution). However in my test file, two of the lossy codecs (Ogg Vorbis and MP2) imparted a lot of clipping, while the third one (MP3) did not. Unless you need absolute minimum file size (say, for e-mailing an audio file) the extreme reductions are probably too much.
The lossy file formats reduce file size by removing repetitive content or content outside the range of human hearing. File size reductions will depend on the exact content of the file, but as a general example (using a couple test files), and standard 44/16 coding:
• WAV = 100%
• AIFF = 100%
• MP3 = 22.7% (using 320 kbps)
• Ogg Vorbis = 11.4%
• FLAC = 34 to 59%
• MP2 = 13.6%
Not everyone can handle AIFF files, and some websites (such as BandCamp) will not accept lossy codecs. Others, like YouTube, will ONLY accept MPEGs (which deliver MP3 audio).
Let’s talk file size. Most mail clients have an attachment file size limit of 20MB or less. Online services will deliver larger files.
BandCamp has a 600MB file size limit for uploading, which works out to about 56 minutes in WAV or AIFF, and 2 hours five minutes in FLAC. New users get half that. BandCamp-Pro users (who pay $10/mo.) can upload up to 2GB per file.
YouTube (verified users) can upload up to 12 hours of movie or 256GB, whichever is less.
Burning your file to a CD-R? CD-Rs have a 700MB capacity, which works out to 80 minutes of audio in the CD’s file format (CD-A, which is slightly less efficient than WAV or AIFF [8.75MB/min. versus 10.71MB/min.]).
Audacity has their own file format for saving files, .aup3 (not openable by any other program). This preserves multiple tracking if you’re working on overdubs (which we’ll touch on in the episode on multi-tracking), but saving (or exporting) a file loses all layers of undo.
Let’s talk about undo. When you’re working on a file and you’re not sure you like the change you just made, you can go to Edit – Undo and it’ll show you the last edit you made. If you “undo” it you will go to the previous version. You are limited in the number of undos you can make only by the size of your hard drive to store the intermediates. You can go back 5, 10, 20 or more versions (if you remember where you went wrong). Sometimes, if you’re making a whole lot of changes (doing some cutting-and-pasting for instance) you may want to save more than one version of the file (giving them different names) to compare later.
Nothing is permanent until you save.
ROBERT
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