There are a lot of audio file formats. Here are the ones you encounter most commonly.
Recorded sound consists of fluctuations in electrical current coming off of a microphone or mixing desk. Before computers, you translated that current into tiny smooth wiggles in the shape of the groove cut into a vinyl record, or tiny smooth wiggles in the alignment of magnetic particles embedded in tape. Dragging a needle along the groove or running the tape over a magnet reproduces the original electrical current.
Examples: vinyl, reel-to-reel tape, cassettes
Pros: Analog formats can sound really great if your media are in good condition, and if you’re listening through a good sound system.
Cons: Analog formats can sound terrible if the media get scratched, dusty or demagnetized. You need to be very careful about physical degradation–every time you listen to a tape, you scrape a little bit of the coating off. You can’t make copies of analog media without introducing noise. And analog gear is expensive.
Uncompressed digital audio
Computers convert the electrical fluctuations coming off the mixing desk as a long string of ones and zeroes. You can’t represent a smooth wiggle in discrete increments with perfect accuracy, but if you use enough ones and zeroes, you can get close enough that no one can tell the difference.
Examples: AIFF, WAV, Compact Disc, DAT
Pros: Uncompressed digital audio sounds great, as good as analog at high bit rates. Digital audio files can be copied perfectly as many times as you want. Digital media is cheap.
Cons: Uncompressed audio produces enormous file sizes, ten megabytes per minute at standard CD quality and many times that using higher audiophile settings. That’s a problem if you want to send music over the internet.
Have you ever wondered how court stenographers can write down a word-for-word transcription as fast as everyone is talking? They have a special shorthand that they write with special keyboards. The shorthand is much more compact than full English, but it can be converted back into full English without any loss of detail. Similarly, it’s possible to find redundancies in audio file formats, so you can make them smaller without reducing the sound fidelity.
Examples: FLAC, Apple Lossless
Pros: Somewhat smaller files with exactly the same sound quality.
Cons: These formats are only used by audiophiles and nerds, and not all software can read them. Also, they files are still pretty big.
If you’re willing to sacrifice some detail and nuance, you can shrink your audio files down to a fraction of their original size. Lossy compression is like SparkNotes. The SparkNotes version of War and Peace is much shorter than War and Peace, and it gives you a pretty good idea of what War and Peace is all about. But you lose nuance, and you can’t reproduce all of War and Peace just from the SparkNotes. MP3s are the SparkNotes of sound.
Examples: MP3, M4A, AAC, Ogg Vorbis, all streaming formats
Pros: Lossy compression produces small file sizes, a tenth the size of the original file or less. The more quality you’re willing to sacrifice, the smaller you can shrink the files. That’s crucial if you want do things like stream audio on the web or email files back and forth.
Cons: At higher compression ratios, lossy compression sounds like garbage. The more the audio is compressed, the worse it sounds. Once the audio quality is gone, it can’t be restored.
Other formats to know about
Digital audio workstation (DAW) session files: Each DAW has its own file format: GarageBand, Logic, Ableton, Pro Tools, and so on. A DAW session is really a folder containing the session file itself, a folder full of audio files, and probably various other bits of metadata. Be aware that DAWs can’t open files created by other DAWs, so, for example, you can’t open a Logic file in Ableton. Also, different versions of the same DAW aren’t necessarily compatible with each other either. If you need to convert a session from one DAW to another, the best method is to make stems.
MIDI: Contrary to popular belief, MIDI is not an audio format. It’s more like notation for the computer, a list of numbers specifying what notes should be played and when. To hear a MIDI file, you will need a software instrument to play it back. MIDI files are really tiny.
Notation: Like DAWs, every notation program has its own specific format, so Sibelius, Finale and Noteflight files are not mutually compatible. The good news is that all of these programs can both read and write a generic format called Music XML, and they also read and write MIDI.
Anything in here I missed? Let me know in the comments.