Mastering for iTunes
Since Apple moved to iTunes Plus in 2007, iTunes downloads are 256 kbps AAC.
iTunes uploads require uncompressed, 24 bit .WAV files which are transcoded to 256 kbps AAC further down the line.
Here are some recommended settings when mastering audio for iTunes:
Use a True Peak limiter, like the Maximizer in Ozone 7, to ensure that the margin is set to –1 dBFS. Apple recommends leaving 1 dB of headroom to prevent any clipping from occurring due to the noise added by the AAC encoder.
Forget about the Loudness War and go easy with any compression, limiting or dynamics processing. Compress a track for the purpose of improving the sound quality, not for increasing the volume. SoundCheck in iTunes uses an advanced algorithm to determine perceived loudness (not simply the peak/RMS values), level match each track to –16 dB, and then add this volume information to the metadata in the header of each audio file. A ‘competitive’ track with no dynamic range now sounds less good in iTunes when played next to a track with greater dynamic range.
Use iTunes as a tool to compare your masters to reference tracks from other artists that you like the sound of. With SoundCheck enabled, hearing your tracks side-by-side at the same perceived volume as the work of others can help to determine whether your masters will hold up for an iTunes listener. Adjust your tracks based on your listening, then render and submit the full quality uncompressed .WAV or .AIFF masters to iTunes.
Mastering for SoundCloud
SoundCloud transcodes uploaded audio to 128 kbps MP3 to prepare the audio to stream from the site. If an audio file on SoundCloud is made available for download, the downloaded version will be in the original format.
Uploading an MP3 is redundant since SoundCloud will transcode it anyway, which could in turn introduce more artifacts to audio that’s already compressed. Therefore, the best practice is to upload an uncompressed, 24-bit .WAV file and allow SoundCloud to process it.
Here are some recommended settings when mastering audio for SoundCloud:
Use a True Peak limiter, like the Maximizer in Ozone, to ensure that the margin is set to –0.3 dBFS. This is an acceptable threshold to mitigate most of the clipping that occurs during the encoding process. However, depending on the source material, you may find a margin of –0.5, –0.7, –1.0, or –1.5 dBFS sounds better, with less distortion. In these cases, you simply have to perform trial and error, perhaps by uploading several versions and deleting all but the best sounding one.
SoundCloud does not have a feature like Apple’s SoundCheck, so an audio master destined for SoundCloud has more freedom to raise the overall RMS level for competitive loudness. Consider this a practical and aesthetic choice. Make sure to use volume matching, such as the ‘automatically match effective gain’ feature in Ozone, to evaluate loudness increases objectively.
Using a stereo imaging tool like the Imager in Ozone, narrow the high end between 5–20%. 128 kbps MP3 is the lowest commonly acceptable audio quality. As such, a lot of information is lost during encoding and an extremely wide mix is more susceptible to noticeable artifacts. Ironically, some pre-emptive narrowing can help avoid perceived loss of energy and width.
Mastering for YouTube
YouTube transcodes all uploaded video (and the contained audio) in order to offer streaming qualities at 360p, 480p, 720p, 1080p, 1440p (2K) and 2160p (4K). Youtube uses the H.264 video codec with the AAC audio codec. The quality of stereo audio playback depends on the user selected streaming quality setting as follows:
360p and 480p video will playback audio at 128 kbps
720p, 1080p, 1440p (2K), 2160p (4K) video will playback audio at 384 kbps
YouTube can only down-convert video, so it’s best to upload the highest quality level you can within the H.264 codec. Why not upload a .MOV with uncompressed audio? For best results, YouTube actually recommends uploading media that is already encoded, rather than uploading a .MOV that contains a full quality .WAV file.
Here are some recommended settings when mastering audio for YouTube:
Use a True Peak limiter, such as the Maximizer in Ozone, to ensure that the margin is set to no higher than –1 dBFS.
Not all encoders are created equal. Render from the video editor in full, uncompressed quality for both video and audio, and then audition the audio visual qualities of different media encoders.
The True Peak Limiting option can be enabled right below the Threshold Meter in the Ozone Maximizer.