Two kinds of M4A
M4A is a container, not a sound format, and it holds one of two very different things. Which one decides what the WAV can be:
| Inside the M4A | Where it comes from | The WAV is |
|---|---|---|
| AAC (lossy) | iPhone voice memos on the default Compressed setting, iTunes Store purchases, most downloads and phone recorders | A perfect copy of how the AAC sounds. What the encoder discarded does not come back. |
| Apple Lossless (ALAC) | Voice memos recorded with the Lossless setting, CDs imported as Apple Lossless, Apple Music lossless downloads | The original recording, sample for sample. |
Each result says which kind your file was, so you know whether the WAV is the original sound or a decoded copy of a compressed one.
Lossless voice memos that other tools can't open
The Voice Memos app has an Audio Quality setting (on recent iPhones under Settings, Apps, Voice Memos; on older ones under Settings, Voice Memos). Lossless records Apple Lossless into a file that still ends in .m4a. Chrome, Edge and Firefox have no Apple Lossless decoder, so browser-based converters that rely on the browser fail on these files or call them unsupported, and the memo looks broken.
This page carries its own Apple Lossless decoder, written from Apple's open-source reference. We tested it against FFmpeg on six files — 16-bit and 24-bit, mono and stereo, a memo-style recording, music, white noise (which forces the encoder's uncompressed mode) and a file that starts with silence — and every sample of every file matched FFmpeg's output exactly. The WAV keeps the memo's own bit depth, so “Match the original” produces a file whose samples are identical to what Apple stored.
AAC files come out the exact length
An AAC encoder can't start on the very first sample, so it adds a short lead-in, usually 1,024 or 2,112 samples (about 20–50 ms), and the M4A records how much to skip. Converters that ignore that note leave a sliver of silence at the start and make the WAV slightly longer than the recording. Here the lead-in is dropped and the WAV ends where the recording does. In our test a 3-second, 48 kHz memo came out at exactly 144,000 samples, and a test tone lined up with the original to the sample.
Loud AAC goes above full scale
Decoded AAC is not limited to the range a 16-bit or 24-bit file can store. Music mastered right up to the limit often decodes to peaks above it: our loud 2.5-second test file had 28,954 samples over full scale, peaking at +4.5 dBFS. A 16-bit or 24-bit WAV has to cut those peaks off, which is what you also hear from most players. The result tells you when this happens; choose 32-bit float and the WAV keeps every peak, so lowering the volume in an editor later brings them back undamaged.
Which settings to choose
| The WAV is for | Bit depth | Sample rate | Channels |
|---|---|---|---|
| Editing in Audacity, GarageBand, Reaper | Match the original | Same | Same |
| A video project in Premiere or DaVinci Resolve | 24-bit | 48 kHz | Same |
| A transcription or speech-recognition service | 16-bit | 16 kHz | Mono |
| Burning an audio CD, DJ software, samplers | 16-bit | 44.1 kHz | Same |
| Loud music you will process further | 32-bit float | Same | Same |
Speech services such as automatic captioning and transcription tools generally want 16 kHz mono: a minute is then 1.9 MB instead of 5.8 MB for the same voice memo at 48 kHz. When you change the rate or mix down a Lossless file, the result says so, because the samples are then no longer the original ones.
How big the WAV will be
| One minute of audio | Size |
|---|---|
| AAC M4A, 128 kbps stereo | about 1 MB |
| WAV, 16-bit, 16 kHz, mono | 1.9 MB |
| WAV, 16-bit, 48 kHz, mono (a voice memo) | 5.8 MB |
| WAV, 16-bit, 44.1 kHz, stereo | 10.6 MB |
| WAV, 24-bit, 48 kHz, stereo | 17.3 MB |
A Lossless memo sits in between: Apple Lossless packs the same samples more tightly than WAV, but by far less than AAC. On our 24-bit, 3-second test memo the WAV was about twice the size of the M4A.
Tags and everything else
The title, artist, album, year, genre, track number and comment are copied into the WAV's INFO list, which Windows, Audacity and most audio software read; a voice memo's title comes across as the WAV's title. Cover art isn't copied, because WAV has no standard place for it. Several files can be converted at once and downloaded as a ZIP.
Going the other way, or to a smaller format: M4A to MP3 keeps tags and cover art, WAV to MP3 shrinks a finished WAV, and Increase audio volume makes a quiet recording louder without clipping. To cut a long memo down first, use Trim audio.