Judy Martinez What is “Mastered for iTunes”: revealing the secrets of Apple’s musical mystery
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Those who are looking for various music on the Internet have probably stumbled upon this mysterious mark on many albums, popular and not so. What does she mean? Some kind of magical EQ curve or miracle plug-in? Let’s try to figure it out.
Of course, Apple will never play by the audiophile rules we like. So far, as you can see, there are no highrez, DSD and other goodies. On the other hand, one cannot say that there are wood grouses who do not care about the quality of the music. Quite the opposite. Young Steve Jobs back in 1982 was photographed with his GyroDec vinyl, Threshold amplifiers and Acoustat electrostats. Later, Genelec columns could be seen on his desktop. And the players and Apple phones themselves, no matter what the haters say with their tongues, for their form factor have very decent characteristics and a low level of distortion.
On the other hand, like any business, Apple is primarily focused on making a profit. And, apparently, never having developed a suitable commercial model for lossless music, Apple chose to concentrate on a more mainstream service with compressed audio. Obviously, over time, in this plebeian sector, certain reasons have matured to establish the Mastered for iTunes procedure.
Mastering
Everyone, except for boobies musicians, knows how much trouble and blood modern sound engineering brings. One barbarian does not hesitate to record the original directly into MP3, the other compresses the volume of the phonogram so that guts and beaks come out of it. And no one listens to Bob Katz, who urged not to get carried away with loudness war, because in iTunes you can always equalize the volume using the SoundCheck and ReplayGain functionality.
If you also compress such garbage with codecs with data loss for publication in iTunes, it will turn out to be very bad. Therefore, Apple decided to systematize this process a little.
Unlike other proprietary protocols of the company, the list of requirements for Mastered for iTunes is posted on the corporate website in the form of a 10-page document. Actually, Apple was not going to engage in mastering – that’s why such openness. All preparation of the phonogram for compliance with Masters for iTunes is entrusted to the music publisher, and in return, his album receives a special medal.
First of all, Apple is calling on publishers to use phonograms in hairese. That is, the bit depth of the master was higher than the standard 16 bit / 44 kHz. Although the final AAC file in the iTunes Plus library will only be VBR256, 16-bit, and 44 kHz, the manual emphasizes that it is best to provide a master at 24-bit / 96 kHz.
The next important point is the requirement to avoid clipping in the master soundtrack at the maximum level of 0 dB. Not only is this not the best mode of operation for a DAC. When converting the master file to compressed formats, the maximum level point will inevitably shift beyond 0 dB, which will bring even more clipping and distortion. Therefore, Apple advises for reliability to normalize the peak volume of the album to minus 1 dB. Of course, a soundtrack originally produced according to the screaming laws of loudness war will not improve. But, at least at the stage of converting the master to AAC, it will not add any dirt from the second wave of clipping.
Tools
To bring these simple truths to life, Apple offers several utilities (or AudioUnit-plug-in), with which the phonogram can claim the title of Mastered for iTunes.
The afclip command utility will point to the clipping points in your master – in great detail, with overlap values. Thus, it will be possible to return to editing and fix everything.
The Master for iTunes Droplet tool uses a proprietary SRC resampler to convert WAV or AIFF to 44 kHz compressed AAC Plus. The same operation can be performed through the command line using the afconvert utility.
AURoundTripAAC Audio Unit will allow you to compare the original and converted files.
Can all of the above be considered mastering? Hardly. Peak Volume Mitigation and Clipping Finder look more like a control feature than an artistic feature. Can you call this quality control? Also unlikely. Apple made only recommendations of good intentions and stipulated that it would not refuse to accept clipped tracks. Are these guidelines really helpful? A well-known specialist in the field of mastering, unfortunately, the late Andrey Subbotin, at one time conducted several experiments with coding the original in AAC Plus using the Mastered for iTunes utilities. Indeed, the procedure Apple insisted on made sense.
Reality
Now we’ll see how these recommendations are being implemented. Take Lana Del Rey’s “Ultraviolet” album as an example. The currently available HD version in 24 bit / 44 kHz carries all the hallmarks of the loudness war curse. Powerful dynamic range compression and clipping. Almost all tracks hit 0 dB in loudness and have a very low dynamic range (DR).
DR Peak RMS Duration Track
DR5 0.00 dB -7.49 dB 6:39 01-Cruel World
DR6 0.00 dB -8.37 dB 4:11 02-Ultraviolence
DR6 0.00 dB -8.70 dB 5:42 03-Shades Of Cool
DR5 0.00 dB -8.13 dB 5:52 04-Brooklyn Baby
DR6 -0.02 dB -7.61 dB 4:17 05-West Coast
DR6 0.00 dB -8.08 dB 5:18 06-Sad Girl
DR6 0.00 dB -8.97 dB 3:54 07-Pretty When You Cry
DR5 0.00 dB -7.28 dB 4:31 08-Money Power Glory
DR5 0.00 dB -7.12 dB 3:32 09-Fucked My Way Up To The Top
DR7 -0.02 dB -10.71 dB 4:31 10-Old Money
DR6 0.00 dB -8.06 dB 3:02 11-The Other Woman
DR5 0.00 dB -6.66 dB 5:15 12-Black Beauty
DR7 0.00 dB -9.46 dB 4:31 13-Guns And Roses
DR6 0.00 dB -7.70 dB 4:14 14-Florida Kilos
Lana Del Ray track – Ultraviolence, encoded according to the recommendations of Mastered for iTunes in AAC Plus (16 bit / 44 kHz). The dynamic range is as narrow, but the signal no longer touches 0 dB
Now let’s look at the same track in AAC marked (Mastered for iTunes). Well, that’s another matter. The narrow dynamic range, of course, has not gone anywhere, but there are no clipping points here. Everything that could grow stopped at half a step from 0 dB. The rest of the tracks also show unanimity. Generally speaking, AAC is a really good coder and not as aggressive as MP3. Spectrograms show minimal damage to the original.
Analyzed: Lana Del Rey / Ultraviolence
DR Peak RMS Duration Track
DR5 -0.63 dB -8.49 dB 6:39 01-Cruel World
DR6 -0.34 dB -9.38 dB 4:11 02-Ultraviolence
DR6 -0.65 dB -9.71 dB 5:42 03-Shades of Cool
DR6 -0.60 dB -9.13 dB 5:52 04-Brooklyn Baby
DR6 -0.86 dB -8.62 dB 4:17 05-West Coast
DR6 -0.77 dB -9.08 dB 5:18 06-Sad Girl
DR6 -0.28 dB -9.99 dB 3:54 07-Pretty When You Cry
DR6 -0.29 dB -8.29 dB 4:31 08-Money Power Glory
DR5 -0.56 dB -8.13 dB 3:32 09-Fucked My Way Up To the Top
DR7 -0.89 dB -11.72 dB 4:31 10-Old Money
DR6 -0.77 dB -9.06 dB 3:02 11-The Other Woman
DR5 -0.25 dB -7.67 dB 5:15 12-Black Beauty
DR7 -0.63 dB -10.47 dB 4:31 13-Guns and Roses
DR6 -0.55 dB -8.70 dB 4:14 14-Florida Kilos
DR8 -0.85 dB -12.62 dB 3:45 15-Is This Happiness
Interestingly, the rest of the AAC versions of Ultraviolet – standard, extended and Japanese – had minor discrepancies in peak levels, but, like Mastered for iTunes, did not have clipping. Let’s hope it worked Apple’s recommendations and will work with other goofy and not so sound producers.
Let’s take another release from the girl group Warpaint – the album “Heads Up”. This time not a highrez, but a regular CD. But here, too, there are miracles – a rather liquid sound is compressed in volume, as if we are facing not girlish indie pop, but a whole Napalm Death.
Warpaint track – Above Control, CD (16 bit / 44 kHz). The dynamic range is also terrible, but there is less clipping.
Compared to Lana Del Rey, there isn’t much clipping here. On this track there are “only” 17 points, and on half of the songs it is not at all. By the way, I specifically compared Warpaint with the last album Napalm Death, their DR value is even higher and, by the way, veterans of grindcore have no clipping at all!
Analyzed: Warpaint / Heads Up
DR Peak RMS Duration Track
DR4 -0.22 dB -5.59 dB 4:42 01-Whiteout
DR4 -0.22 dB -6.42 dB 4:32 02-By Your Side
DR4 -0.22 dB -5.77 dB 4:16 03-New Song
DR5 0.00 dB -6.06 dB 4:56 04-The Stall
DR5 0.00 dB -6.55 dB 5:59 05-So Good
DR5 -0.22 dB -5.64 dB 3:43 06-Don’t Wanna
DR5 -0.22 dB -7.95 dB 4:22 07-Don’t Let Go
DR5 -0.22 dB -6.64 dB 3:59 08-Dre
DR5 -0.10 dB -7.00 dB 4:57 09-Heads Up
DR5 0.00 dB -6.25 dB 5:06 10-Above Control
DR10 -0.22 dB -12.01 dB 4:49 11-Today Dear
Clipping will no longer be available in Mastered for iTunes. All peaks prudently stopped in hundredths of the 0 dB fatal mark. I also draw your attention once again to the sparing work of the AAC codec that Apple uses for encoding. The high-frequency spectrum is a little thinner, but no cutoffs that MP3 can afford.
Warpaint track – Above Control encoded according to the recommendations of Mastered for iTunes in AAC Plus (16 bit / 44 kHz). There is no clipping and the frequency range in the HF region is more or less intact.
Analyzed: Warpaint / Heads Up
DR Peak RMS Duration Track
DR4 -0.37 dB -6.09 dB 4:42 01-Whiteout
DR4 -0.15 dB -6.92 dB 4:32 02-By Your Side
DR5 -0.19 dB -6.28 dB 4:16 03-New Song
DR5 -0.27 dB -6.57 dB 4:56 04-The Stall
DR6 -0.25 dB -7.05 dB 5:59 05-So Good
DR5 -0.52 dB -6.14 dB 3:43 06-Don’t Wanna
DR6 -0.21 dB -8.46 dB 4:22 07-Don’t Let Go
DR5 -0.32 dB -7.14 dB 3:59 08-Dre
DR5 -0.15 dB -7.51 dB 4:57 09-Heads Up
DR5 -0.03 dB -6.76 dB 5:06 10-Above Control
DR10 -0.51 dB -12.51 dB 4:49 11-Today Dear
Apple can be scolded for its lack of interest in lossless music, but where it gets to work, you can count on a certain level of quality. And what is called mastering is still on the conscience of musicians and publishers.
Based on materials from “Stereo & Video” magazine, April 2017. www.stereo.ru
