WAV or AAC — which recording format to choose
The short answer: WAV if you are going to transcribe or edit it, AAC if you only need to listen back. The single difference is whether the audio is compressed, and everything else — size, quality, what you can do later — follows from that.
What actually differs
WAV writes down the measured numbers as they are. Nothing is processed, so the files are large, but nothing that was captured is lost.
AAC makes the file smaller by throwing away the parts a human ear is unlikely to notice (lossy compression). What it discards does not come back. That is fine for listening, but it means speech recognition receives less information than was recorded.
Size
| Format | Per hour |
|---|---|
| WAV 48 kHz, 24-bit, mono | about 518 MB |
| WAV 48 kHz, 16-bit, mono | about 346 MB |
| AAC 128 kbps | about 58 MB |
| AAC 64 kbps | about 29 MB |
That is close to a factor of ten. If you want hundreds of hours sitting on the device, use AAC. If you process recordings one at a time and move them off, use WAV.
Choosing by purpose
| Purpose | Format | Why |
|---|---|---|
| Transcribing | WAV | What compression removes is what recognition needs, especially quiet voices and consonants |
| Editing and publishing | WAV | Every edit and export re-compresses, and the damage accumulates |
| Just listening back later | AAC | A tenth of the size, and faster to share |
| Keeping it as a record | WAV | An unprocessed file is harder to argue with afterwards |
Bitrate, if you choose AAC
For speech, 64–96 kbps is usable and 128 kbps leaves nothing to complain about for listening back. Going higher than that is hard to hear on a voice-only recording.
What each app supports
| iOS | WAV only (16-bit / 24-bit integer, 32-bit float). It is built around transcription |
|---|---|
| Android | AAC (.m4a, LC / HE, 64–256 kbps) and WAV (PCM16) |
Questions
Can I convert WAV to AAC afterwards?
Yes. The other direction does not work — strictly speaking AAC can be written out as WAV, but what was discarded stays gone and you only get a bigger file. When in doubt, record WAV.
Can it record MP3?
Not as a recording format. You can open and work with MP3 and other common formats that already exist.
WAV does not fit on my device
Lowering the sample rate and bit depth helps more than changing format. At 48 kHz, 16-bit, mono an hour is about 346 MB. If that is still too much, split at a fixed interval and export as you go.