M4A or WAV? Choosing a format, sample rate and bitrate

Four settings decide how a recording sounds and how much room it takes. You can set them per recording in Custom mode, or leave the presets alone and never think about them again.

Format

• M4A (AAC) — compressed. Roughly a tenth the size of WAV at a quality most people cannot tell apart from the original on a phone. The right default for voice.
• WAV — uncompressed. Every sample kept, every editor reads it, files are large. The right choice for music and for anything you will edit repeatedly.

Sample rate

How many times a second the sound is measured: 8 kHz is telephone quality, 22.05 kHz covers speech comfortably, 44.1 kHz is CD quality, and 48 kHz is what video uses. Higher costs size and does nothing for a voice.

Bitrate

How much data a second of M4A gets, from 64 to 320 kbps. 64 kbps is fine for one person talking; 128 kbps is the safe middle; above 192 kbps only matters for music, and for music you should be in WAV anyway. Bitrate does not apply to WAV — its size is decided by sample rate and channels alone.

Mono or stereo

Mono is one channel, stereo two. A stereo file is twice the size and tells you where a sound came from. A single voice gains nothing from stereo; a room, a band or a street does.

Roughly what an hour costs

• M4A 22.05 kHz 64 kbps mono — about 28 MB.
• M4A 44.1 kHz 128 kbps mono — about 56 MB.
• M4A 44.1 kHz 256 kbps stereo — about 113 MB.
• WAV 44.1 kHz mono — about 300 MB.
• WAV 48 kHz stereo — about 350 MB.

Set your own

1. Open Settings from the app.
2. Under Recording, tap Audio quality.
3. Pick Custom, then choose format, sampling rate, bitrate and channels.
4. Record from the Custom card and those settings are used every time.