AURoundTripAAC – A/B Testing

If you missed the Mastered for iTunes tools that Apple released at the beginning of this year you should take a look and grab the AURoundTripAAC Audio Unit if you want to test if you can hear the difference between your source material and the resulting encoded file.

My results were about what I expected. I did VERY well hearing the difference at low bit rates.


16kpbs is like shooting fish in a barrel. If I bump it up to 96 things get a little tricker for me:


So I think 256kpbs AAC files will be just fine for my listening.

Apple’s Mastered For iTunes Pages

Finally some explanation direct from the source:

An ideal master will have 24-bit 96kHz resolution. These files contain more detail from which our encoders can create more accurate encodes. However, any resolution above 16-bit 44.1kHz, including sample rates of 48kHz, 88.2kHz, 96kHz, and 192kHz, will benefit from our encoding process.

Now this is a little different that just boosting EQs for white earbuds. They are starting with the high resolution audio and encoding that down, rather than going through all that for a CD and then encoding the CD and sending that to Apple. The iTunes Producer software sends your music to Apple to sell in iTunes used to just encode your CD as Apple Lossless and upload it to Apple. Looks like this is changing.

I still get wary when an audio engineer says they’d still pick the CD as the highest quality commercial release. And how, if iTunes is still publishing these songs as 44/16 AAC files, is this different than doing this same downsample and dithering process for a 44/16 CD?1

This bit is interesting. Apple is trying to serve as the archive of nearly all digital masters.

…though it may not be apparent because there may not always be a physical, tangible master created in LP or CD format, the iTunes catalog forms an important part of the world’s historical and cultural record. These masters matter—especially given the move into the cloud on post-PC devices.

  1. Looks like there may be at least a couple of reasons, like built-in soundcheck profiles and 32-bit floating-point files used during sample rate conversion. 

Mastering for iTunes

Digital Music News interviewed Vlado Meller, the mastering engineer on the new Red Hot Chili Peppers album, which has three masters: one for CD, one for vinyl, and one for iTunes.

Digital Music News: What specific considerations play into the AAC mastering process? Can you really make a version that brings white earbuds to life, or is that not the point?

Meller: Yes, with an iTunes optimized master, the listener will be able to enjoy more clarity and an overall better sound quality than is otherwise currently available.

I hope this doesn’t become a standard practice, because it seems like a load of bull. Meller even states that he’d pick the CD version as the “highest quality” for commercial release.

Back in 2009 I wrote:

…mixing for a certain encoder means giving those encoders a pass. Better to let the flaws of the encoder shine through so that the market can choose to not use that encoder and move on to something better.

Since the launch of iTunes Plus we’ve learned that most people still can’t hear the difference between 256kbps AAC and 128kbps AAC. And people already had a hard time hearing the difference between a 128kbps file and the original CD.

If the CD is the true master then why create an iTunes specific master? Hype is my guess. Maybe it will persuade people to buy two copies of the album—a CD for the car and the download for the office.

When you hear people talking about mastering for iTunes are they really talking about mastering for AAC or are they’re talking about mastering for white earbuds?

Mixing for MP3 Is Stupid

In my opinion.

Once in a while I’ll read something about mixing engineers and how they create different mixes for CDs and digital music services. The arguments are that encodes don’t recreate certain frequencies well, like anything below 100hz. So because of that they may suggest boosting the low-end on anything that will be used for an MP3 encode.

I think this is a bad idea.

I think mixing and mastering engineers should work on music for ears, not encoders. These days, bitrates for digital music stores are about 256k, which may as well be lossless for most people. And someday we all may get lossless encodes – which leaves a catalog of mixes that were poorly engineered in the hopes of making up for the weaknesses of an MP3 encoder.

Plus, there are so many variables to think about (which mp3 encoder? bitrate? AAC/WMA/OGG?) that trying to create the perfect mix for each of them means chasing your own tail, and it doesn’t account for the fact that I, and many others, will be ripping the official mix to a digital format anyway.

Besides, mixing for a certain encoder means giving those encoders a pass. Better to let the flaws of the encoder shine through so that the market can choose to not use that encoder and move on to something better.

However, I think you should arrange your album for digital formats. Please spare us hidden tracks or 5 minute stretches of silence that were a trend during the 90s. Downloading a 10meg file of 256k CBR encoded silence is obnoxious.

Lovin’ The Amazon MP3 Store: The AAC/MP3 Fidelity Argument

MP3 vs AAC

I’ve been getting upset that AAC hasn’t gotten as much support as MP3, but the more I think about it the more I realize that MP3 is the smarter choices for these stores. I prefer AAC, but MP3 has wider compatibility and has much larger recognition behind it. MP3 is synonymous with digital music.

The other part of wanting AAC over MP3 is the encoding quality, but things have changed. The codec used to matter when bitrates hovered around 128-192kbps. Now that everything is basically 256kbps it’s a wash. It doesn’t matter anymore.

The file sizes are the same and you’ll have a hard time telling the difference between AAC and MP3 at these bitrates. Don’t even try. Stop worrying about codecs and start listening to more of the music you love.

The iTunes “Last Chance” Playlist

If you’ve read the iTunes Zero article you’ll know that I’m very meticulous about everything in my iTunes library – and chances are you probably do the same things.

One of the other problems you may be facing is that there’s SO MUCH STUFF in your iTunes library. How do you handle it all?

Here’s what works for me – the “Last Chance” Playlist.

The Process

Here’s the method I use when I add new music to iTunes and homogenize it into the library:

  1. Everything new goes into a static Process playlist. It’s a holding cell for me to verify the metadata before I’m comfortable unleashing it into the wild. Consider it the GTD inbox for iTunes.
  2. Music that hasn’t been listened to shows up in the Playcount = 0 smart playlist.
  3. 3 months after that first listen, music shows up again in the Only 1 Listen playlist. This is my opportunity to make sure that the assigned rating is what I want it be, because after that it’s banished into the iTunes abyss, until the special day when it arrives in the…
  4. Last Chance playlist.

You’re Up For Review, Tune

Why do this?

The purpose of the Last Chance playlist is to listen to tracks in shuffle mode, out of context, in order to rate each track on its own. Let’s take a look at its properties.


The Last Chance smart playlist is the last hurrah of a misfit song. If after two years I still don’t like the song enough to give it a 4-star or higher rating, in it goes to the huge library, likely to be skipped over and ignored for the rest of eternity.

But, there’s the chance that after 2 years I’ll suddenly realize the genius in a song, and grant it a 4-star or higher rating and save it from the 82 gig (as of this writing) Rancor pit.


And with a 4-star or higher rating, the track enters regular rotation in smart playlists that rely on ratings.

This works for me for the following reasons:

  1. Anything I’ve already rated on the extremes (2 stars or less, or 4 stars or more) doesn’t really change for me – but I’ve still got my eye on those 4-star rated tracks.
  2. 3 listens should be enough for me to know if I like a song or not.
  3. 2 years (or 1 year) is far enough out for a song to be removed from the popular culture of the time to realize I like a song because it’s a good song, and not because it’s in a car insurance commercial or something.

This is what works for me. Storage is cheap these days, so if you set up a system with this and other smart playlists you can keep only the good stuff on your iPod and regular playlist (or Party Shuffle sources) and not have to delete anything based on the idea that you might like it years from now.