Convexy

Convert WAV to M4A on iPhone

A first-generation AAC encode from a lossless source. This is how you turn an unmanageable WAV into something you can actually send, store and play — with the smallest quality cost the format allows.

Why WAV files are a problem

WAV is uncompressed PCM — every sample written out in full, nothing discarded, nothing packed. That is exactly what you want from a recording master and exactly what you do not want from a file you have to email, upload or carry around.

Stereo 44.1 kHz 16-bit audio costs roughly 10 MB per minute. An hour-long interview is over half a gigabyte. A three-minute demo is 30 MB. Nothing about that is broken; it is simply the price of storing every sample.

This is the good kind of lossy conversion

AAC — the codec inside an M4A — is lossy. It permanently discards audio the encoder judges you will not perceive. That is unavoidable and true of every AAC file ever made.

What makes this conversion clean is that your source is lossless. The encoder receives the real, complete recording and makes its decisions once, with full information. This is a first-generation encode — the best AAC this recording can produce.

It is a fundamentally different operation from converting an MP3 or another M4A to M4A, where a second encoder compounds damage a first one already did. The rule holds everywhere in audio: encode once, from the best source you have.

Why M4A and not MP3

Both are lossy; AAC is the better codec. It was designed later, it is more efficient at any given bitrate, and the gap widens as bitrates drop. For anything staying inside the Apple world, M4A is also simply the native citizen:

Choose MP3 instead when the destination is old hardware — a car head unit, gym equipment, a DJ controller — where MP3's thirty-year head start is the deciding factor. Convexy can produce either from the same WAV.

What Convexy writes

Convexy encodes the M4A with Apple's own AAC exporter, on the device, at its standard high-quality setting. There is no bitrate dial for M4A output — Apple's exporter does not offer one — so you get a sensible, conservative encode rather than an opportunity to pick the wrong number.

If you specifically need to control the bitrate (say, a podcast host that mandates 128 kbps), encode to MP3 instead, where Convexy exposes 128, 192, 256 and 320 kbps along with sample rate and channel controls.

Keep the WAV if the recording matters. Once the M4A exists, the audio the encoder discarded is gone from it permanently, and converting the M4A back to WAV later will only produce a large file containing the same damaged audio. If the WAV is an interview, a gig, a take or a field recording you cannot repeat, archive it — or convert it to FLAC, which is lossless and about half the size.

Expect a very large size drop

This is the whole point of the exercise. A 60-minute WAV of around 600 MB will typically land somewhere in the tens of megabytes as an M4A — a reduction of roughly 10:1 or better, depending on the material and the encoder's decisions.

That is not a trick and it is not a compromise you should feel bad about. It is a psychoacoustic codec doing precisely the job it was designed for, on a clean source, exactly once.

How to do it

  1. Bring the WAV into Convexy

    Tap Browse files and pick it from Files or iCloud Drive, or share it in from whichever app recorded it.

  2. Choose M4A

    Convexy lists only formats a WAV can genuinely become — M4A, MP3, AIFF, CAF and FLAC.

  3. Convert

    Apple's AAC encoder runs on your iPhone. A long recording takes a moment; nothing is uploaded at any point.

  4. Save or share it

    Rename the output if you need a particular filename, then save it to Files or send it straight on.

Common questions

Does WAV to M4A lose quality?

Yes — AAC is lossy and permanently discards audio. But this is a single encode from a lossless source, which is the least harmful way to make one. Nothing had been thrown away before the encoder saw the file, so it makes its decisions with complete information. That is a very different thing from transcoding an MP3 or an existing M4A.

Should I choose M4A or MP3 for my WAV?

M4A if the destination is anything Apple, or anything modern — AAC is the better codec and the file will be smaller at the same quality. MP3 if the destination is old hardware: car stereos, gym equipment, DJ gear, or any form that says "MP3 only". Convexy makes both from the same WAV, and you can make both.

Can I set the M4A bitrate?

Not for M4A — Convexy encodes it with Apple's AAC exporter at its standard high-quality setting, and that exporter does not expose a bitrate control. If you need a specific bitrate, convert to MP3 instead, where 128, 192, 256 and 320 kbps are all selectable.

Can I convert the M4A back to WAV if I need the original?

You will get a WAV, but not the original. Decompressing a lossy file recovers only the audio that survived the encode — everything AAC discarded stays discarded, and the WAV will simply be large. If the recording is irreplaceable, keep the real WAV, or archive it as FLAC.

How much smaller will the file get?

Typically around ten times smaller, sometimes more. Uncompressed stereo audio costs roughly 10 MB per minute; an AAC file of the same audio is usually a couple of megabytes per minute or less. The exact figure depends on the recording.