File Formats

File formats and how to deal with them

(© Jeffrey de Gans v1.5, 18 September 2019)

There are a lot of misconceptions about the various audio formats, streaming services, how they work and how to deal with them. In this article I will try to give you some information about that. Since this information is constantly changing, I will try to keep this up-to-date.


Streaming services and loudness normalization

By now you probably know that all streaming services use loudness normalization. This means that no matter how loud it is, it will always play back at the same perceived loudness. This is true, but on the other hand it’s not and that is where things could go wrong. The biggest misconception is that you should master your music to -14LUFS, because it will simply be turned down otherwise. This is not true.. As a matter of fact, I don’t think it’s a good idea to master to -14LUFS at all! Pop, Dance, Rock, EDM will most likely miss ‘power’ when mastered to -14LUFS because the limiting and compression is ‘part of the sound’. But also, what about Apple music, they are at -16LUFS? So you need multiple masters for all of the streaming services? That is not what you want! You just want one master that will sound great on all streaming platforms. This simply means, as a mastering-engineer, I will just make it sound great and don’t focus on the numbers. If a master sounds great at -13LUFS, fine. If a masters sounds brilliant at -6LUFS or even louder, great! It’s not about numbers, it’s about music. Sure those louder masters might be turned down more to get to the right level, but then it still sounds great.

Spotify is (at least in the EU) market leader when it comes to streaming services and Spotify uses loudness normalization by default since day one. There is one problem with that normalization, there are 3 settings which is cool, but.. The ‘Quiet’ setting is normalizing to -23LUFS** so that for instance a playlist with low level material next to louder material will still sound pretty equal in level. The ‘normal’ setting is at -14LUFS** and leaves music which is less loud alone, it will simply play back less loud. Then there is the ‘loud’ setting, which is normalizing at -11LUFS**, and that is where thing can go wrong. In this case, it will normalize the music to -11LUFS, but.. less loud music will be internally limited (!) to get to -11LUFS. So your precious, dynamic master will be squashed with the Spotify limiter. This is one of the reasons why I prefer to make masters for streaming that come close to -11LUFS or louder to prevent this. But as said before, it’s not about the numbers, it’s about how it sounds.

** Spotify uses ReplayGain, which is not the same as LUFS and using K-weighting. This means that their -14LUFS is actually not -14LUFS and could vary depending on the balance of the music. Spotify announced the use of LUFS/K-weighting in the near future.

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Youtube is using loudness normalization for quite some time now, though some older movies and audio is (was?) for some reason not normalized. This meaned that those old movies could turn up way louder then newer movies. Pretty much the same as with the commercials that popup before a movie starts. I personally think that those loud commercials work in the opposite of what they want to achive with it, but that’s maybe just my idea. Think about that yourself and how your response is when that happens and how it would be if it was equally loud as the movie you just watched before.

Since the start, the normalization was set to -13LUFS, but this was not the real LUFS standard and so it could vary which could mean a not so pleasent surprise. Since 19 September YouTube started using the real LUFS standard using K-weighting and they are now normalizing to -14LUFS.

For those interested in the actual normalization, you can check (on a pc or mac, not your phone) by right clicking (or ctrl click on mac) on the movie and click on ‘stats for nerds’. there you can see the actual normalization levels. 100% means that the level of your player is set to 100% (fully open), the value next to it is how much it has been turned down.

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Apple Digital Masters (formerly Mastered For iTunes) is based on uploads in 24bit, 44.1khz (or higher) WAV files with true-peak detection after conversion to AAC+ by using their own tools. Only approved/certified by Apple mastering-engineers can deliver those Apple Digital Masters (ADM) masters. So in case you asked for ADM masters, make sure you mention my name and email address or they will be rejected by Apple.

There is a misunderstanding that you always need Apple Digital Masters for Apple Music, this is not true. Regular streaming masters will work fine for standard Apple Music. But if you go for the highest possible quality and the ADM batch on your release, you need appoved ADM masters.

Read more about Apple Digital Masters info here

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September 2019: Amazon Music just announced that they will roll out lossless streaming, even in 24bit resolution when available! Hooray!

But what about the distributors that just support 16bit upload?
If you’re an independent artist, band, or record label that uses services like Tunecore and CD-baby, I would strongly urge you to write to your distributor and insist they start accepting 24-bit WAV masters so that at least your future releases can be enjoyed in the highest quality available.

‘I deliver high resolution 24bit masters along with 16bit masters as a standard since day one’

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Uploading to digital distributors/services do’s and don’ts


Nowadays people use distributors like Distrokid, Tunecore, CD Baby to get their music online. This is great of course. Think of it like distributors of CD’s/vinyl records back in the days. They took care of the delivery to all record-stores, even the ones you didn’t even knew existed.

The majority of distributors/aggregators still require 16bit 44.1khz WAV files for basic upload. Some of them, like Distrokid, supports 24bit with 44.1khz (or higher) WAV files which is great, because that will sound better when converted to a lossy format. On the other hand, some aggregators also seem to support the upload of MP3 files instead of WAV files, which is a BIG No-Go! When you do that you will get ‘transcoding’, meaning 2 layers of lossy encoding on top of each other and that will really mess up the sound. This is also one of the biggest mistakes that people make when they upload their music to SoundCloud or Bandcamp. They upload an mp3 with ISP’s and wonder why it sounds so bad. Always upload 24bit WAV files to SoundCloud and Bandcamp and use the streaming master that I delivered with a max true-peak of -1dBFS.

All music on Spotify, Apple Music etc have one thing in common, they all have an ISRC assigned. WAV files nowadays are BWAV files (which is an old standard really) which supports metatags like ISRC codes, titles, engineers, artwork, you name it. I can embed all that information for you if you want me to. This is great of course, but there is one thing which is not so great. When you upload using an aggregator/distributor you still need to fill in that information by hand, even if it’s embedded in the WAV file in the standarized way. So make sure that you fill in the ISRC codes when uploading or you might be surprized that they assigned another ISRC code to your track because you didn’t fill it in yourself. I’m not aware of any distributors reading the metatags right now (september 2019), hopefully that will be the case soon.

More info on ISRC codes can be found here

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Use WAV files in 16bit (or 24bit if possible) to upload to distributors/aggregators
NEVER use MP3 files to upload to distributors/soundcloud/bandcamp
Use streaming masters (STREAM in filename) to upload to distributors
Apple Digital Masters (ADM in filename) for official ADM release (mention my name/studio)
Add ISRC codes yourself during upload even if they are embedded in the masters

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Physical Mediums and file formats


Even though in 2019 streaming is the default medium for listening to music, the physical product market is still there as well. It actually got bigger compared to a couple of years ago. People still like to have something physical like a CD or vinyl record.

Those physical products need a different approach then a digital release when it comes to mastering. You need dedicated masters for Vinyl and a DDP image for CD. Read more about this below.

Vinyl is hip and happening and more and more artists release their music on vinyl again. There are some things to keep in mind though, because a standard digital master will most likely not work on vinyl. For vinyl, you don’t want a crushed, clipped, limited master, it will work in the opposite of what you might think. For vinyl you need optimized masters (there are a lot of variables to take into account) that could be cut to a Lacquer or DMM by a cutting-engineer for the best result.

When you ask for vinyl masters, we will also discuss ‘what should be where’ when it comes to the ABCD sides and things like that. I will deliver one long 24bit WAV file per side with the right transitions between the tracks including information on where to put the pause bands/spirals for the cutting-engineer.

I always insist on getting a ‘test-pressing’ to make sure that the vinyl record will sound as what you had in mind. I’d like to listen to that test-pressing in my own studio using my own calibrated environment but if you have the possibilities to check in a proper way yourself that is also fine of course.

There is a maximum of audio which can be cut to vinyl and even though they are just rough numbers, they will give you some guidelines to keep in mind.

12 inch @ 33RPM: Optimal 16 to 20 minutes, max 25 minutes
12 inch @ 45RPM: Optimal 6 to 12 minutes, max 15 minutes

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Even though CD’s are not as big as back in the days, they still excist and people still buy CD’s, just on a different level. For a CD release you need a DDP image, a 100% error-free digital image of the CD. This DDP image will be send directly to the CD factory and they will press or duplicate the CD’s from this image. All tracks, including the right transistions will be there, but also all information like CD-text, UPC/EAN and ISRC codes. Before I can make the DDP image, I need all that information like the titles and things like that. But also ISRC codes should be embedded and they should be the exact same code as the digital release. So make sure you get that information to me before I start mastering by using this excell sheet.

To check the DDP image yourself before sending it to the CD factory, you need a DDP player. You can download my DDP player by following this link.

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I use a standarized filenaming structure for masters that I deliver. This will avoid confusion and using the wrong masters. During upload of masters, especially to new clients, I will also send a PDF file  with all the information below.

Depending on the types of masters you asked for and what format you delivered the mixes in, this is what your masters will look like. Let’s presume the delivered mix was in 24bit 96khz and was named 01 Songtitle.wav, the mastered files will be named like this.

01 Songtitle (mastered 17-4).wav (24bit 96khz master, same resolution as mix)
01 Songtitle (mastered 17-4) 1644.wav (dithered 16bit 44.1khz master, most common) *
01 Songtitle (mastered 17-4) ADM.wav (Apple Digital Masters in 2496) **
01 Songtitle (mastered 17-4) VINYL.wav (vinyl master in 2496)
01 Songtitle (mastered 17-4) STREAM 1644.wav (16bit 44.1khz stream master, spotify etc) ***
01 Songtitle (mastered 17-4) STREAM.wav (24bit 44.1khz stream master, soundcloud etc) ****
01 Songtitle (mastered 17-4) mp3 320kbps.mp3 (320kbps mp3 from high res master)

The (mastered 17-4) part means that the mastering took place on the 17th of april. In case you ask for a revision which is delivered the day after, the file-name will be ‘01 Songtitle (mastered 18-4).wav’. When I send you a new version the same day, it would be ‘01 Songtitle (mastered 18-4 v2).wav’. So you can always see which is the last version and when the mastering took place.

* 16bit 44.1khz masters (1644) are the most commonly used masters for download portals etc

** Apple Digital Masters (ADM) are 24bit files dedicated for the Apple Digital Masters (formerly known as Mastered For iTunes) program. Only certified mastering-engineers (I am) can deliver official ‘ADM’ Masters, so you need to point out that I was the engineer that did the masters or they will be rejected.

*** Streaming masters in 16bit are dedicated masters for streaming services like Spotify, Deezer, YouTube, etc.

**** Streaming masters in 24bit are dedicated masters for streaming services like SoundCloud, bandcamp or distributors that support 24bit WAV file upload.

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Mastering is the final step before your music is released to the world. I take that very seriously.”

With kind regards,

Jeffrey de Gans | Da Goose Mastering