Recording · glossary
M4A file
Also called MPEG-4 Audio, .m4a, AAC file
An M4A file is an audio-only MPEG-4 file, usually holding sound compressed with AAC. Voice Memos and many other iPhone apps save recordings as .m4a, and most phones and computers play it without extra software.
M4A stands for MPEG-4 Audio. It uses the same container as an .mp4 video, with only an audio track inside, and Apple’s iTunes made the .m4a extension common. Most M4A files hold AAC, a lossy codec that throws away detail you are unlikely to hear so the file stays small. Some hold ALAC (Apple Lossless) instead, which keeps every bit of the original at about half the size of uncompressed audio.
The size difference is easy to picture. Three minutes of CD-quality WAV (44.1 kHz, 16-bit stereo) takes about 32 MB. The same three minutes as 256 kbps AAC in an M4A takes under 6 MB.
You meet M4A files as soon as you record on an iPhone, because Voice Memos saves its recordings as .m4a. Drop one into a DAW such as GarageBand and it becomes a track you can trim and overdub new parts over. If a program only accepts WAV, converting to WAV loses nothing more. Converting from one lossy format to another, such as M4A to MP3, costs a little quality each time, so keep the original.
Gelato Synth and Gelato Chord, our iPhone apps, both record everything you hear, effects included, to an .m4a file and then open the share sheet for AirDrop, Messages or Files.
To take a hummed idea further, see how to turn a voice memo into a song. How to make music on your iPhone covers the rest of a phone recording setup.
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