Convert M4A to WAV

When a recording has to be WAV

M4A is a good format for keeping recordings small, but some of the tools you'll use next are fussier:

• Transcription and speech-to-text services that list WAV as the format they prefer, or the only one they take.
• Audio editors that work faster on uncompressed sound, or older ones that won't import M4A at all.
• Research and analysis software, for speech or acoustics, that expects plain PCM.
• Video projects, where a 48 kHz WAV lines up cleanly with the picture.

WAV is the plain, uncompressed format they all understand. Converting doesn't change how a memo sounds; it just takes it out of its compressed form so the next program has nothing to decode. Keep the M4As as well: they are the small originals, and you can make new WAVs from them whenever another tool asks for different settings.

Settings for speech tools and editors

Check what your service asks for: many speech tools are built around 16 kHz mono, 16-bit, and say so in their help pages. A higher bit depth (24-bit or 32-bit float under More settings) adds nothing to AAC sound, but gives an editor extra headroom if you'll push the levels around. Put these back as they were resets every setting in one click when the next batch needs the defaults again.

What converting does, and doesn't do

For AAC memos and songs, the WAV is a faithful copy of what the M4A plays. Nothing more is lost, and nothing comes back: detail the AAC encoder dropped stays dropped. For Apple Lossless M4As, such as lossless Voice Memos and ALAC songs, the WAV is an exact copy, sample for sample, and a 24-bit file stays 24-bit.

The price is size. A memo of about 1 MB a minute becomes a WAV of 5 to 11 MB a minute, depending on the sample rate and channels. For a long interview, 16 kHz mono keeps that under 2 MB a minute, the very format many speech tools are built around, and an hour comes to about 115 MB instead of the 690 MB of a 48 kHz stereo WAV. If an editor wants 24-bit files, choose that under Bit depth: the extra bits won't change the sound, they just match what the program expects.

Names, tags and privacy

Each WAV keeps its M4A's file name, so “Interview 3.m4a” becomes “Interview 3.wav” in the same folder. The title and other tags are written into the WAV too, though few programs display WAV tags; the cover picture of a song is left out. To collect all the WAVs in one place for uploading, set Save in to A folder I choose… before converting.

Interviews, meetings and voice memos stay on your PC while they are converted, with no upload step, which keeps sources and conversations confidential until you decide where they go next. A day's worth of interviews can go in as one batch: four are converted at a time, each row counts down its time left, and the rest wait their turn.