What File Format Should I Send for Mastering?
If you’re exporting a finished mix for mastering and wondering what file format to use, the simple answer is: send a WAV file.
A WAV is the safest, most widely compatible option and lets you send your mix without throwing away any audio information. If you’re exporting directly from your DAW, I’d normally suggest a 24-bit WAV at the same sample rate you’ve been working at.
That said, WAV isn’t some magical mastering format. AIFF is absolutely fine too, FLAC is lossless and perfectly usable, and if an MP3 is genuinely the only version of a song that still exists, I can work with that as well. The important thing is to send the best-quality source you actually have rather than converting files back and forth just because you think mastering requires a particular extension.
If you’re looking for the full checklist rather than just the file-format question, read How Should I Export My Mix for Mastering?.
The Simple Answer: Send a WAV File
For most people, WAV is the obvious choice.
It’s uncompressed, widely supported and can carry the full-quality audio coming out of your mix session. Pretty much every DAW will give you WAV as an export option, and you don’t have to worry about whether whoever is mastering the track can open it.
If you’re exporting a new file specifically for mastering, 24-bit WAV is a great default. If your DAW is already working with or exporting 32-bit float, that’s absolutely fine too. There’s no need to convert a perfectly good 32-bit float file down to 24-bit purely because you’ve heard that mastering engineers want 24-bit files.
Likewise, there’s no benefit in taking an existing 16-bit file and converting it to 24-bit before sending it. Changing the number written on the file doesn’t somehow add detail that wasn’t there in the first place.
The basic rule running through all of this is pretty simple: export from the original mix session at the best quality available and avoid unnecessary conversion.
WAV vs MP3 for Mastering
If you have the choice between WAV and MP3, send the WAV.
MP3 is what’s known as a lossy format. To make the file much smaller, some audio information is discarded during encoding. That’s extremely useful when you want a small file for listening, sending around or sticking on an ancient MP3 player you inexplicably refuse to throw away, but it’s not ideal as the source for mastering.
A WAV exported directly from your mix session hasn’t gone through that lossy compression stage, so I’ve got the best possible version of your mix to work from.
That doesn’t mean an MP3 suddenly becomes unmasterable, though.
Can an MP3 Still Be Mastered?
Yes.
If an MP3 is genuinely the best version of the song that exists, I can still master it. Maybe the original project is long gone, the producer disappeared into the wilderness years ago, or you’ve found an old track on a hard drive and the MP3 is all that survived. In that situation, send the best-quality version you have and we work with it.
What I wouldn’t recommend is deliberately exporting an MP3 for mastering when you still have access to the original mix session and can export a WAV instead.
It’s really just about giving the mastering process the best starting point available.
Does Converting an MP3 to WAV Improve the Quality?
No.
This is an easy trap to fall into because once you convert the file, your computer will indeed tell you that you now have a lovely WAV file. Unfortunately, the audio inside it has still already been through MP3 compression.
Converting an MP3 to WAV does not restore the information that was discarded when the MP3 was created. You’ve essentially put the existing MP3 audio into a larger container.
So if somebody has sent you an MP3 and you’re about to convert it to WAV before sending it for mastering, there’s no need. Send me the original MP3 instead. Better still, if the original mix session or lossless export still exists somewhere, go back to that and export a fresh WAV!
Is AIFF OK for Mastering?
Absolutely.
AIFF and WAV are both perfectly suitable formats for a full-quality mastering source, and there’s no reason to convert a good AIFF into WAV purely for sound quality.
I tend to recommend WAV simply because it’s the most universally familiar choice and tends to create the least confusion. But if your mix already exists as a full-quality AIFF, send the AIFF.
Is FLAC Suitable for Mastering?
Yes, FLAC is fine too.
The important distinction here is that while FLAC is a compressed format, it uses lossless compression. In other words, it reduces the file size without throwing away audio information in the way MP3 does.
I accept FLAC files for mastering, so if you already have a proper lossless FLAC of your mix there’s no need to panic and convert it simply because you’ve read somewhere that mastering has to be done from WAV.
Again, though, if you’re sitting in your DAW about to create a brand-new mastering export, I’d still choose WAV. It keeps things simple.
What Bit Depth Should I Use for Mastering?
If you’re exporting a new mix, 24-bit is a straightforward default.
32-bit float is also completely fine, particularly if that’s how your DAW handles its exports. You don’t need to reduce it to 24-bit for my benefit.
What I wouldn’t do is start converting files between bit depths after the fact because you think there’s a particular number you need to hit before mastering. If the mix already exists as a good-quality lossless file, send that rather than creating another generation unnecessarily.
And if all you have is a 16-bit WAV, that can still be mastered. Just send the original 16-bit file rather than converting it to 24-bit to create extra resolution, sadly it won’t!
Sample rate and dithering are related to all of this, but they’re really separate questions in their own right. For the purposes of this article, the useful rule is to keep the mix at the sample rate it was actually recorded and mixed at rather than converting it just for mastering.
The same goes for some of the other advice you’ll often see bundled in with mastering export settings. File format doesn’t determine how loud your mix should be, so if that’s what you’re trying to work out, I’ve covered How Loud Should My Mix Be Before Mastering? separately. There’s also no need to use normalisation to make the file hit a particular target, which I explain in Should I Normalise My Mix Before Mastering?. And if you’re wondering whether the processing on your master bus should stay there, have a look at Whether You Should Remove The Limiter Before Mastering.
Summary
If you’re making a fresh export, send me a 24-bit WAV at the sample rate you’ve been working at and you’ll be in good shape.
If you already have a full-quality AIFF or FLAC, that’s absolutely fine too. If your export is 32-bit float, there’s no need to convert it down first. And if the only surviving version of the track is an MP3, it can still be mastered, but it should really be treated as a last resort when no higher-quality source is available.
Above all, don’t get too caught up trying to manufacture the “correct” mastering file. Send the best-quality version you have, avoid unnecessary conversions, and if you’re unsure, just ask.
If you’ve got a mix ready and want me to check what you’ve exported before we get started, you can send it over here. I’m always happy to have a listen and let you know if you’ve got the right file.