Compress WAV File on iPhone

Someone sends you a WAV of an interview and it is 400 MB. You export a mix from a recording app and it will not attach to an email. A voice recording of a two hour lecture eats more storage than a film. This is not a bug and the file is not badly made. It is simply what WAV is.

The fix is easy once you understand what you are actually trading away, which is the part most guides skip straight past on their way to recommending a website.

Why WAV files are so large

A WAV file usually holds raw uncompressed PCM audio. Every sample of the waveform is written out in full, with nothing removed and nothing predicted. You can calculate the size exactly, which you cannot do with any compressed format.

Take standard CD quality: 44,100 samples per second, two bytes per sample for 16 bit depth, two channels for stereo. That is 176,400 bytes every second, which works out to roughly 10 MB per minute. An hour is around 600 MB. Move up to 24 bit at 48 kHz, which is common for anything recorded properly, and you are at roughly 17 MB per minute.

Nothing is wasted in there. It is a complete, exact record of the audio, and that is precisely why studios, archives and mastering engineers use it. It is also why it is impossible to email.

Two different things called compression

Worth separating these, because searching for this phrase turns up both and they have nothing to do with each other.

File compression makes the file smaller in bytes. That is what this article is about.

Dynamic range compression is an audio effect that reduces the gap between the loudest and quietest parts of a recording, making a track sound more even and usually louder. It changes how the audio sounds and it does very little to the file size. If that is what you came for, you want an audio editor, and this is the wrong page.

Lossless first, if quality is non-negotiable

Before throwing anything away, know that there is a middle option. Lossless compressed formats like FLAC and Apple’s ALAC store the exact same audio in roughly half the space. Decompress one and you get back a bit for bit identical waveform. Nothing is lost, ever.

If you are archiving masters, or handing files to someone who is going to edit them further, this is the correct answer and you should not be considering anything lossy.

The catch is that iOS does not make this easy from the share sheet, so it is realistically a desktop job or a task for a dedicated audio app. Grabio does not do lossless audio conversion, and I would rather say that than let you install it and find out.

The practical route on a phone: convert to M4A

For almost everything that is not a studio master, converting to M4A is the right move. M4A uses AAC, which is a modern lossy codec, and at sensible settings it sounds very close to the original while being a fraction of the size. Apple’s own apps produce and prefer it, Voice Memos records in it, and everything in iOS handles it without complaint.

On the phone:

1. Find the WAV in the Files app.
2. Tap the share icon.
3. Tap Grabio in the action list.
4. Choose the M4A tool.
5. Save the result.

There is a fuller walkthrough with the edge cases in converting an audio file to M4A on iPhone. Grabio also has a Compress tool that works on audio, useful when a file is already in a compressed format and was simply exported at a needlessly high bitrate.

Grabio is a free iOS Shortcut. No App Store install, no account, no paid version to run into halfway through the job.

When MP3 is the better choice

M4A is the better format on technical merit. MP3 is the better format on compatibility, and compatibility often wins.

Pick MP3 when the file is leaving the Apple world: going to someone on Windows, into a car stereo that reads a USB stick, onto old hardware, into a system whose supported formats list was written in 2008, or to a radio station or a client whose requirements say MP3 and will not be argued with.

Nothing made in the last thirty years fails to play an MP3, and that is worth more than a small quality edge.

The steps are in converting audio to MP3 on iPhone. My own rule is simple: staying on my devices means M4A, going to anyone else means MP3.

How much smaller, realistically

The size of a lossy file is set by its bitrate, and the relationship is straightforward. A minute of audio at 128 kilobits per second is about one megabyte. So an hour long interview that was 600 MB as a WAV becomes roughly 60 MB at that bitrate.

What bitrate to pick depends on the material. Speech survives low bitrates remarkably well, because the human voice occupies a narrow band and there is not much detail to lose.

Music needs more, particularly anything with cymbals, strings or reverb tails, where low bitrates produce a distinctive watery smearing. If you are unsure, err higher. The file is still going to be an order of magnitude smaller than the WAV.

WAV quirks worth knowing

A few things about the format that surprise people.

• There is a size ceiling. The classic WAV header uses 32 bit fields for size, which caps a file at around 4 GB. Long high resolution recordings genuinely hit this, and the recorder either stops or splits the file.
• Metadata support is poor. Artist, album and artwork do not travel reliably in a WAV. If you want tagged files that look right in a music app, a converted M4A or MP3 is actually better in this respect.
• WAV is a container. Almost always it holds uncompressed PCM, so people treat the words as interchangeable, and almost always that is fine.

The other way to shrink an audio file: get rid of what you do not need

Before compressing, check whether the whole recording needs to exist. An hour of a two hour lecture is half the file. Silence at the start and end of a take is pure waste. Cutting first and compressing second always beats compressing a file that is half dead air, for the same reason it works with video.

And if the audio you are wrestling with is stuck inside a video file, extract it rather than compressing the video. An hour of audio is smaller than a minute of 4K footage, so this is by far the biggest reduction available when it applies. That is covered in extracting audio from a video on iPhone.

If the destination is email and you are fighting an attachment limit, the same tactics apply as with video, and compressing for email goes through the actual limits. Past a certain size, sending a link beats sending an attachment, which is the argument in sending a large file from an iPhone.

What I would do

Keep the WAV if it is a master, a recording you will edit, or something irreplaceable. Storage is cheap and re-recording is not. For every other purpose, listening, sharing, sending, archiving a copy, convert to M4A and let the original sit on a drive somewhere.

Doing that conversion on the phone takes two taps from the share sheet. Get the Shortcut if you want it there. It is free, there is no login, and it covers the other conversions you run into as well, which are listed in converting any file format on iPhone.

Frequently asked questions

Why are WAV files so big?

Because they store audio uncompressed, writing out every sample in full. At CD quality that is roughly 10 MB per minute, and higher sample rates and bit depths push it further. The size is the price of keeping a complete, exact copy of the waveform.

Does converting WAV to M4A lose quality?

Yes, since AAC is a lossy codec that discards information it predicts you will not hear. At reasonable bitrates most people cannot tell the difference in normal listening. Keep the WAV if the file is a master or will be edited further, because each lossy re-encode costs a little more.

What is the best format to compress a WAV into?

M4A if the file is staying in the Apple ecosystem, since AAC sounds better than MP3 at the same size and every Apple app handles it. MP3 if the file is going anywhere else, because its compatibility is unmatched. FLAC or ALAC if you need the audio bit for bit identical at about half the size.

How much smaller will my file get?

Roughly one megabyte per minute at 128 kilobits per second, against about ten megabytes per minute for a CD quality WAV. So expect something close to a tenfold reduction at that setting. Higher bitrates give you better quality and a proportionally larger file.

Can I compress a WAV on iPhone without a computer?

Yes. Grabio is a free iOS Shortcut with audio conversion tools that run from the share sheet, so you share the file, pick M4A, and save the result. It needs no App Store install and no account, and there is no paid tier.

Is there a size limit on WAV files?

Around 4 GB, because the standard WAV header stores sizes in 32 bit fields. Long recordings at high sample rates do reach this in practice, at which point a recorder either stops or splits into multiple files. Compressed formats have no equivalent ceiling in normal use.