How to export a correct audio file and master your music for streaming

Every track you upload to the Content Portal is checked automatically before we deliver it to Spotify, Apple Music and the other stores and streaming services. This article explains what a correct audio file looks like, how to export one from your software, and what to look out for when you master your own music to ensure it sounds how you intend it to on every platform.

Audio file requirements

Your audio files must meet all of the following requirements. Files that do not meet these requirements will be rejected by the Content Portal or by our Digital Distribution team.

A real WAV file

Changing the extension of a file (for example from .mp3, .m4a or .aiff to .wav) does not convert it into a WAV file. The audio inside stays in its original format and our system will reject it. Always export a new WAV file from your original project instead.

Converting an MP3 or another compressed file to WAV does not help either. The file may be accepted, but the quality lost during compression does not come back. Always start from your original, uncompressed mix or master.

Export, don't save

Besides the audio itself, a WAV file has a header and can hold extra data, such as markers, project information or broadcast details. Media players simply ignore this, so a file can play perfectly on your computer. The systems that process your upload are much stricter: they need a clean header and nothing but audio. Extra data and damaged files are the most common reasons for rejection.

Many programs add this extra data when you use Save or Save as. To get a clean file, always use the Export function of your DAW or mastering software. Depending on the program, it may be called Export, Bounce or Render.

Figure 1. Exporting creates a clean WAV file. Saving can add extra data.

When you export:

• Choose WAV as the format and PCM as the encoding.
• Set the bit depth to 16 or 24-bit, and keep the sample rate of your project.
• Switch off options such as Broadcast Wave (BWF), "include metadata", markers or iXML if your software has them.
• Check your settings carefully if you use Logic Pro as it is known for adding extra data to WAV files, which our system almost always rejects.

Is your file still rejected even though you exported it correctly? Then the file may be damaged. Export it again from your project and upload the new file. If that does not help, contact us at support.

Loudness: mastering for streaming

Every track plays at the same loudness

Spotify, Apple Music, YouTube and most other services use loudness normalisation. They measure how loud each track is and turn it up or down, so listeners do not have to reach for the volume button between songs.

Loudness is measured in LUFS (Loudness Units relative to Full Scale). Unlike a regular peak meter, LUFS reflects how loud music actually sounds to the human ear. It is an international standard, also known as LKFS.

Spotify plays music at -14 LUFS by default. Premium listeners can also choose Loud (-11 LUFS) or Quiet (-19 LUFS). This applies to all formats, including lossless. Apple Music does something similar with its Sound Check feature. Spotify's recommendations below are widely seen as the industry standard, and they work well for all the other services too.

Figure 2. Loud masters are turned down. Quiet masters are turned up only if there is room.

Louder is not better

Making a master as loud as possible no longer gives you an advantage. A track mastered at -7 LUFS is simply turned down by 7 dB. Because it has been squeezed hard by a limiter, it then often sounds flatter and weaker than a more dynamic track at the same volume. A very quiet master, on the other hand, is only turned up as far as its peaks allow, so it can end up sounding quieter than other tracks.

Spotify recommends the following for your master:

Figure 3. Spotify's recommended targets.

• Integrated loudness around -14 LUFS. This is the average loudness of the whole track.
• True peak no higher than -1 dBTP. This leaves room for the conversion to compressed formats like AAC and Ogg Vorbis.
• True peak no higher than -2 dBTP if your master is louder than -14 LUFS. Loud masters create more distortion when they are converted.

These are guidelines, not strict rules. How loud or dynamic your music is remains an artistic choice. But if you stay close to these values, your music will sound the way you intended on every platform.

True peak and clipping

A digital file cannot go louder than 0 dBFS. Anything above that is cut off, which is called clipping and sounds like harsh distortion. Even if your meter never touches 0 dBFS, the signal can still go over it between two samples when it is played back or converted to AAC or MP3. These are called inter-sample peaks.

A true peak meter (dBTP) also measures these peaks. That is why you should use a true peak limiter on your master with its ceiling set to -1 dB, and check the result with a loudness meter.

Apple Digital Masters

Apple Digital Masters is Apple's name for high-quality masters on Apple Music and iTunes. It was previously known as Mastered for iTunes. Apple converts your master to AAC for streaming and to Apple Lossless (ALAC) for lossless listening.

Apple's best practices are good advice for every platform:

• Supply 24-bit masters at the highest native sample rate. Apple handles the conversion to lower sample rates with high-quality tools.
• Do not upsample. Converting a 44.1 kHz file to 96 kHz, or a 16-bit file to 24-bit, does not add any quality.
• Leave at least 1 dB of headroom to avoid clipping during playback and conversion.
• Check the result. Apple offers free tools for Mac to hear exactly what your track will sound like on Apple Music and to check it for clipping, including inter-sample peaks.
• Remasters must be noticeably better. A remaster has to start from a new high-resolution transfer of the original analogue source, and must sound clearly better than the earlier release.

The tools and Apple's full technical guide are available on the Apple Digital Masters page. Note that only Apple accredited mastering engineers can create true ADM masters and you must supply their details to us when you need an ADM badge. Contact support if you don’t have access to an accredited mastering engineer; we may be able to assist.

Tools to check your master

You do not need expensive software to check your master. Many DAWs have a built-in loudness meter, and there are excellent free plugins. A selection (prices at the time of writing):

Checklist before you upload

Figure 4. From master to upload.

1. Master with a true peak limiter, with the ceiling at -1 dB.
2. Measure the whole track with a loudness meter and aim for around -14 LUFS integrated.
3. Export (do not save) a WAV file: PCM, 24-bit, at the sample rate of your project, without metadata or BWF.
4. Check the file: play it back from start to end and look at the format details.
5. Upload the file to the Content Portal.

More information

• Loudness normalization (Spotify for Artists)
• LUFS (Wikipedia)
• Apple Digital Masters (Apple)
• WAV (Wikipedia)