The library / Formats
Four questions.
One audio file.
A filename extension tells only part of the story. Start by separating the package from the sound it contains.
What holds the data?
A container packages audio and may also hold tags and artwork. A codec describes how the audio itself is represented or compressed. Those two roles are related, but they are not interchangeable.
What has been preserved?
| Type | Examples | Useful distinction |
|---|---|---|
| Uncompressed PCM | WAV, AIFF | Large files; metadata support depends on software. |
| Lossless compression | FLAC, ALAC | Can reconstruct the encoded PCM data exactly. |
| Lossy compression | MP3, AAC | Trades some information for smaller files. |
How often, and at what resolution?
Sample rate describes the number of samples per second for each channel. Bit depth describes the numerical resolution of PCM samples. These figures describe a file; they do not, by themselves, establish that one master sounds better than another.
Which copy should you keep?
For an archive, retain the best available original you are entitled to keep. Converting a lossy file into FLAC cannot recover information that was already discarded. Make smaller listening copies separately if you need them.