Mastered for iTunes


To be clear, Mastered for iTunes is not so much a format. It is more a process attached to a format. While to some, it might just represent the pretty label on their latest iTunes store purchase, for musicians, engineers and music appreciators it is the beginning of a whole new golden standard of digital music delivery.

Before the foray of the MP3 in the mid 90s, the three major formats of mass music delivery were vinyl records, the cassette tape and the compact disk. The quality of the music contained on these delivery formats was universally quite good. Even the cassette tape was capable of sounding great. In fact, in almost all cases, it was the player that was the hindrance for delivering high-quality sound; your audio quality was only ever as good as the player because the source itself was excellent.

With the advent of the iPod came the proliferation of MP3s. The iPod put the capability of playing back full-resolution audio in your pocket. With its built-in digital to analog converters – which essentially allow you to hear the digital files in the analog world – being well above standard, the most portable high-quality audio experience was available to the masses.

The files available on the iTunes store and on the Internet at that time were 128kb MP3s, which was the first iTunes standard. They were of much lower quality than the iPod was capable of playing. These MP3s were encoded from the 16-bit production CD and captured at the lowest acceptable encoding setting for music. Artists, engineers and audiophiles were extremely unhappy about this. The sub-par quality of 128kb made it impossible to reproduce the subtleties and presence in the recordings.

Why is high-quality audio better? Think of high-resolution audio like organic food. It’s closer to the source with no unnecessary additives. It’s more like nature intended it to be. And in the case of audio, nature is the artist, producer and engineer. The more degraded the quality of audio becomes, the further away it gets from what they intended it to be.

The problem with MP3 and AAC audio is that it is lossy data-compressed. This means that part of the audio frequency spectrum has been taken away to make for less data and a smaller file size. Your ear doesn’t hear these frequency removals due to a concept called “perceptual coding” in which louder frequencies mask quieter frequencies. Think of it as an optical illusion for the ears. The problem with this is that while you think your brain doesn’t hear these missing frequencies, there is indeed another part of your brain that is aware they are missing. We know for a fact that people prefer non-data-compressed audio to data-compressed-audio in blind listening tests, and frequency masking is one of the many reasons why.

After many years of justified complaints from artists, producers, engineers and music-lovers, Apple decided it was time to rewrite its process of encoding audio. In consultation with producers, recording and mastering engineers, the Production and Engineering Wing of the Grammys and Apple technicians, they set out to develop a set of standards and better the AAC codec to increase the quality of audio available on the iTunes store.

What they came up with was Mastered for iTunes (MFiT). Paired with the AAC+ codec, it includes tools, directions and standards that allow the mastering engineer to increase the quality of audio files provided on the iTunes store. This is a very good thing for everyone.

The format for MFiT is an enhanced AAC file. It’s still a data compressed codec like MP3, but unlike the 16-bits MP3, this particular AAC file is encoded from and decoded to 24-bits of audio information. This makes it above the 16-bits standard of an audio CD, MP3 or standard AAC file. While the difference between 16 and 24-bits is subtle and while you might not think you hear it, even the most un-trained ear can perceive it. The higher the quality of audio, the better it makes you feel and the more you enjoy it. There is just something about it that is innately better since most recording and mastering studios operate at 24-bits.

The process for Mastered for iTunes is two-step. First is a set of guidelines laid out by Apple to prepare and audition your file specifically for iTunes delivery. Second is a set of specifications for the actual delivery and testing of the source master file.

The first process happens while in the creative mastering stage. This is where engineers can make decisions based on how it is going to sound in iTunes. Apple provides guidelines to tell the mastering engineer how to prepare the master for optimal encoding. It also provides tools so the engineer and artist can audition how it will sound with the iTunes enhanced AAC codec. If it doesn’t sound right, the mastering engineer can make changes based on this. Unlike MP3 encoding which can be done with one of many different codecs, a Mastered for iTunes AAC codec is always the same so the mastering engineer will know what the final product sounds like when it arrives in the iTunes store.

It is a small yet revolutionary change for the industry. Never before in the MP3-age has a mastering engineer been able to control exactly what the end file will sound like. In the past, mastering engineers have been able to make a PMCD Master for CD, or a vinyl test-press – or acetate – for records, in order to preview what the final product would sound like. This was wiped out by the MP3. An artist and engineer could labour endlessly getting an album to sound exactly the way they wanted, only to have it be compressed to a low bit-rate MP3 using an inferior converter. Instantly all the presence they worked so hard to create would be lost. Thanks to Mastered for iTunes, we now have the tools to preview exactly how the higher quality audio will sound upon digital delivery.

In the second part of the MFiT process, Apple allows the engineer to send up to a 24-bit-rate 96khz sample-rate file – much like the bit-rate, generally the higher the sample-rate the higher the quality. Apple then uses its proprietary system to sample-rate convert and then encode the 24-bit non-dithered file directly to AAC format.

Wait, what is “non-dithered”? Dithering is a method of adding noise to mask quantization errors which could cause distortions when converting from 24-bit of information to 16-bit. That noise doesn’t data-compress well and it’s one of the reasons why MP3s often don’t sound very good. Mastered for iTunes avoids this by converting 24-bit files, which don’t need the addition of dithering.

Here is a Mastered for iTunes for comparison. In this folder you’ll find the original 24bit 96khz mastered album, the 16bit 44.1khz CD, 320kb MP3 version and the Mastered for iTunes files. Load them into your DAW and decide for yourself what you like best.

Want to see what you’re hearing?

320kb MP3 FileiTunes.JPG


Visually, you can tell that more high frequency information is getting through in the MFiT version. While this is far from scientific since the MP3 can be encoded so many different ways –this one was done at 320KB from our mastering software (Magix Sequoia)– it is perhaps an indication that the true quality of the song is coming through more clearly via the higher quality file.

Regardless of one’s opinion on the sound of Mastered for iTunes, the reality is that there are approximately 250 million iOS devices out there in the hands of consumers in over 50 countries across the world that are served by an iTunes store. It goes without saying that is a massive amount of ears listening to music. The biggest player in audio technology and digital music distribution has listened to the artists and professionals it serves and has made audio quality a priority. While Mastered for iTunes is a technology at its infancy, it has the potential to become the first true standard for high-quality digital audio that will be adopted on a broad scale.

Without the distinction of a Mastered for iTunes label, consumers of audio won’t really know, by looking at the file, if it’s MFiT or not. It’s a transparent process and compatible with all versions of iTunes and iPods. As the technology gets better, or new operating systems are released, Apple will update the audio files to match it — via, appropriately enough, iTunes Match cloud server service — since they have the hi-res source files from the mastering studio.

This opens the door for artists and engineers to also consider remastering previous catalogue work for iTunes – taking physical masters and transferring them into a digital archive that offers exact, bit-for-bit copies without any signal degradation.

It appears the industry is moving towards a complete adoption of this new standard, for good reason. Overall, there is dramatic potential for iTunes files to be many times higher quality than their predecessor, the CD.
If you want to provide your fans with the best chance to hear your music precisely as you intended it to sound then Mastered for iTunes should be a serious consideration when mastering your next project.



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