Convexy

Convert AIFF to MP3 on iPhone

AIFF is the Mac's uncompressed audio format — big, lossless, and awkward to share. MP3 is small and plays anywhere. Encoding one from the other is straightforward and, done once from a lossless source, about as clean as lossy gets.

What AIFF is, and why you have one

AIFF (Audio Interchange File Format) is Apple's uncompressed PCM container — the Mac's answer to WAV, and older than it. Same idea: the raw sample values written straight to disk, nothing discarded, nothing compressed. The only real difference from WAV is byte order and the header layout, which is a detail no listener has ever noticed.

It is lossless and uncompressed, so it is large: a stereo 44.1 kHz 16-bit AIFF runs about 10 MB per minute, the same as WAV.

Most AIFFs turn up from one of three places: an export from Logic or GarageBand, a CD ripped on a Mac before AAC took over, or a sample library. All three are the kind of thing you want to keep as a master and share as something smaller.

This is a first-generation encode

MP3 is lossy — the encoder permanently discards audio it judges you will not miss. That part is true of every MP3 ever made and no app can avoid it.

What makes this conversion the good kind is that AIFF is lossless. The MP3 encoder is handed the real, undamaged audio and gets to make its decisions once. Nothing has been thrown away before it arrives. Contrast that with converting an M4A or an existing MP3 to MP3, where a second encoder compounds losses that a first encoder already inflicted — the result there is audibly worse and unnecessarily so.

From a lossless AIFF at 320 kbps, you are getting the best MP3 this recording can produce. That is the whole ballgame.

iOS ships no MP3 encoder. Apple's frameworks read MP3 but cannot write it, and never could — the MP3 encode format does not appear in the system's list of available encoders. Every MP3 patent expired in April 2017, so this is a product decision, not a legal one. Convexy includes the LAME encoder and does the work on your device.

What to set

Bitrate. 320 kbps for music, full stop. 256 kbps (Convexy's default) is a defensible compromise. 128 kbps is for speech and for upload forms with a hard cap — it is not for a mix you spent a weekend on.

Sample rate. Leave on Preserve. If the AIFF came out of a DAW at 48 kHz and the destination insists on 44.1 kHz — some podcast hosts and CD-oriented tools do — set it explicitly rather than leaving it to chance.

Channels. Preserve for music. Mono for a single-microphone voice recording, which halves the file for nothing you will miss.

An AIFF of a 4-minute track is around 40 MB. The 320 kbps MP3 will be about 10 MB. That is the trade, stated plainly.

Keep the AIFF

Once the MP3 exists, the audio the encoder removed is gone from that file permanently. Converting it back to AIFF later produces a 40 MB file containing 10 MB worth of surviving audio — bigger, not better.

If the AIFF is a master you want to keep but the size irritates you, convert it to FLAC instead. FLAC is lossless and compressed: about half the size, decoding back to the exact same samples. Then make MP3s from the FLAC whenever you need them.

How to do it

  1. Bring the AIFF into Convexy

    Tap Browse files and pick it from Files or iCloud Drive, or share it in from the app that exported it.

  2. Choose MP3

    Only formats an AIFF can genuinely become are offered — MP3, M4A, WAV, CAF and FLAC.

  3. Set bitrate and channels

    320 kbps for a mix or a master. Mono at 128 kbps for a spoken-word recording that has to fit an upload limit.

  4. Convert

    LAME runs on your iPhone. Nothing is uploaded, no account is involved, and it works with the network off.

  5. Save or share it

    Rename the file if the destination is fussy about names, then save it to Files or share it on.

Common questions

Is AIFF the same as WAV?

Effectively, yes. Both are uncompressed, lossless PCM containers of the same size for the same audio. AIFF is Apple's, WAV is Microsoft's, and they differ in byte order and header structure — not in what you hear. Converting between them changes the wrapper, not the sound.

Does AIFF to MP3 lose quality?

Yes — MP3 discards audio permanently, by design. But this is a single encode from a lossless master, which is as good as an MP3 gets. At 320 kbps from a clean AIFF, the loss is not the thing you will notice on a phone, in a car, or on ordinary speakers.

What bitrate should I use?

320 kbps for music. 256 kbps if you want a smaller file and are not agonising over it. 128 kbps only for speech, or when a submission form imposes a size limit you cannot argue with. Mono is a bigger and safer saving than a low bitrate when the source is a single voice.

Can I get the AIFF quality back from the MP3 later?

No. Converting MP3 back to AIFF gives you a file roughly ten times larger containing exactly the same audio the MP3 already had — everything the encoder deleted stays deleted. Lossless formats preserve what you give them; they do not reconstruct what is missing. Keep the AIFF.

Why can't the Files app or Voice Memos do this for me?

Because iOS has no MP3 encoder to call. Apple's audio frameworks decode MP3 but cannot create it, so no built-in app can offer MP3 output — and a converter app that does either bundles its own encoder or uploads your file to a server. Convexy bundles LAME and keeps everything on the device.