From a raw stream to a Mac-friendly file
Mac audio programs are built around AIFF and WAV. GarageBand and Logic Pro do read AAC, but raw .aac files without an MP4 container are a different story: some versions refuse them, others import them with a wrong length. Final Cut Pro and older Mac tools can be similarly picky. Converting AAC to AIFF gives you a clean, uncompressed file that every Mac application accepts and that edits without delay.
Where these AAC files come from
Raw AAC usually is not something you choose. It appears when you extract the sound from a video with a simple tool, record internet radio, save a Bluetooth or call recording, or receive audio from certain Android apps. These files are fine for listening, but awkward to edit. AIFF turns them into ordinary project material.
Quality and size
Decoding adds no further loss, and nothing that the AAC encoder removed comes back. In practice that means the AIFF sounds exactly like the AAC. The file becomes much bigger:
- AAC at 128 kbps: about 1 MB per minute.
- AIFF, 16-bit, 44.1 kHz stereo: about 10.6 MB per minute.
- AIFF, 24-bit, 48 kHz stereo: about 17.3 MB per minute.
For material from an AAC file, 16-bit already captures everything there is. Choose 24-bit only so the file matches a 24-bit session and the program does not convert it on import. A sample rate of 48 kHz suits video work in Final Cut or iMovie; 44.1 kHz is common for music.
Working with the result
Since raw AAC has no tags, the AIFF will have none either, so name your files clearly before importing. If the AAC came from a screen or call recording, you may want to clean up the sound: the noise reduction tool removes hiss and hum, and normalize brings quiet recordings to a good level. If you also work on Windows, the same audio in WAV is more widely supported. For listening on an iPhone, keep the AAC or turn it into M4A, which is far smaller.