Mastered for iTunes – friend or foe?

Engineer Wes Maebe on why his reaction to the arrival of Apple’s MFiT concept was one of excitement, not disapproval.

Apple’s Mastered for iTunes (MFiT) came to the fore a few years back and caused quite a stir in the mastering community.

I for one got quite excited. Finally, a tool for us to combat the constant requests for ridiculously loud masters. Final master levels have been gradually increasing over time and mastering engineers are caught between a rock and a hard place. On the one hand, mastering is the final step in the quest for sonic excellence and on the other, mastering engineers get asked to make the material louder than everything else that’s come before.

What is MFiT?

MFiT’s strap line is “Music as the artist and sound engineer intended”. Now that sounds good to me. However, it’s not possible yet to purchase full-resolution files through iTunes. All your work will be converted into a lossy, data-compressed 44.1kHz Advanced Audio Codec (AAC) file.

When you’re mastering for data-reduced user formats like AAC and MP3, there are a couple of issues to keep an eye and ear on.

One of the challenges with working in the digital domain is sample rate conversion. Hopefully you’ll be recording and mixing with higher sample rates like 48, 96 and 192kHz. MFiT expects a 44.1kHz/24-bit wav file to be delivered. So, inevitably, there will be sample rate conversion happening as the final step. This is no different when you’re working for CD. What is different though, is that MFiT has made the dither step obsolete. You no longer need to dither down to 16-bit.

The other important factor to keep in check is Inter-Sample Clipping. ISC can occur when the digital convertor reconstructs the signal to be fed to the analogue output. Heavy limiting and loud masters suffer more from this and the distorting result is far from pleasing.

And this is what brought me to the whole MFiT movement. Apple provides a couple of tools to check on ISC and these allow you not to master too hot. The RoundTripAAC plug-in gives you information on how hard you are clipping your actual output and your AAC converted output. It shows you the amount of clipping and Inter-Sample Clipping in the left and right channels. It also allows you to audition the original and encoded output.

Coupled with RoundTripAAC, you have a Terminal command called afclip. The afclip readout is basically a numerical version of the plug-in. It’ll display the time and the samples where ISC occurred, in which channel it happened and how loud it was. Personally, I like to combine this auditioning process with the Sonnox Fraunhofer Pro-Codec. That way you can also check on compression formats other than AAC.

I’ll take you through my trip so far in the MFiT story. Hopefully this will help spread the word. It’ll raise some issues, flag up some pit falls, but more than anything, I’d like more of us to talk about it and form a united front against over-compressed and distorted audio.

I can hear you say: ‘Oh no! Not that old whining story about loudness again.’ Well, yes. None of us have anything against loud music but when that loudness starts messing with the quality of the audio that we’ve worked so hard for, when it causes hearing damage, that’s when we have to make a stand and stop it!

Many, myself included, welcomed the MFiT protocol with open arms. We saw it as an ally in our fight against audio degradation. This was going to be our tool that would allow us to keep severe clipping at bay. I also like that I have access to clip amounts and a couple of red lights so I can explain to the client that there is a loss of quality going on.

The MFiT tools are freely available online and they come with a 10-pager on how to implement them. I’ve been using their tools and have been delivering MFiT files for a couple of years now.

Imagine my surprise when, after all this time, an aggregator comes to me and tells me that my MFiT files cannot be submitted to iTunes because I am not an iTunes-approved mastering house.

Even though there is no mention of this anywhere in their documentation, you need to be approved by iTunes. After a couple of emails back and forth, yours truly is now MFiT approved. The guys at Apple couldn’t have been more helpful. Up to this point, MFiT requests hadn’t been rolling in that frequently. More recently it’s been a common occurrence.


In the meantime I’m hearing some negative MFiT comments from a couple of colleagues. The feeling seems to be that it’s all a marketing ploy; they don’t really care about the quality, etc. Wanting to protect my newfound anti-loudness friend, I started to do some research. I downloaded a newly released Mastered for iTunes album by a major artist and checked it out with the RoundTripAAC and the afclip tools. Result: 3,092 Clips and 12,554 Inter-Sample Clips.

Here we are struggling to keep ISC to low hundreds – I try to keep it as close to zero as possible – and then there are major labels issuing releases that stomp all over the principle of the whole thing.

Apple is investigating the issue – fingers crossed for a positive outcome. There are no hard and fast rules to MFiT. It is left to the taste and discretion of the mastering engineer. Therefore it is important for all of us to raise awareness, maintain a healthy discussion and keep educating listeners.

Wes Maebe is a UK-based recording, mixing, mastering, and live sound engineer.