“Apple Digital Masters” (formerly Mastered for iTunes) is a declaration by Apple which guarantees that the music for sale on iTunes is exactly what the artist and engineers intended. To accomplish this Apple has developed a series of software tools which allow engineers and producers to preview high resolution masters with the same compression algorithm which Apple uses to create it’s ACC file for sale on iTunes. In short, Apple has opened up their encoding process to accommodate high resolution recording.
A. If you are an artist and you want the “Apple Digital Masters” badge on your iTunes page then you will need the following:
- Make certain the mastering house/engineer is “Apple Digital Masters” Certified.
- Make certain that your music is recorded and mixed at a minimum sample rate of 44.1khz and a minimum bit depth of 24 bits, however Apple prefers 96khz/24 bit. DO NOT down/upsample or dither the bit depth. If you record at 48khz/24 bit, then keep your mix at 48khz/24 bit. Make sure that your mixing engineer and mastering engineer understand this because it is common practice for engineers to convert audio to a CD ready format which is 44.1khz / 16 bit audio prior to sending material for digital distribution.
- After you receive your masters from the mastering house make certain the files are the same resolution as your recording.When submitting material to iTunes directly or through an aggregate make certain to declare your intention to receive the ADM certificate.
- When submitting material make certain to include the name of the mastering house and email of the mastering engineer. The engineer will be contacted by Apple for verification.
There it is! It’s that simple. Please contact andy@audiobaymastering.com with any questions.
B. If you are an engineer you may be interested in a more technical breakdown:
1) Apple prefers mastered audio files at 96khz/24 bit, but any sample rate with a bit depth of 24 or higher will still be considered an “Apple Digital Master.” The reason Apple wants 96/24 is so they can start with the highest resolution material for better conversion and for future archiving in the event iTunes improves its algorithm to a higher encoded resolution (it’s now 256kbs, but more on this in a second).
2) The mastering house does not encode the material, iTunes does that. But Apple has developed a number of tools engineers can use to preview the final product using the exact same algorithm that iTunes uses. This ensures that the engineer is aware of any sonic issues which could occur during the encoding process.
3) iTunes uses an AAC encoder with an algorithm which produces a very accurate playback file (ACC file). If a few common sense guidelines are followed during the mastering the ACC file result can be a stunning replica of the original high resolution mix:
a) Roll back the volume a touch. A song with a little headroom is going to encode noticeably better than a mix which is flat-lined at -.1db. The reason being is that iTunes outputs its ACC file a bit louder than the source file. There is some intersample overs which occur that aren’t always detected by normal peak meters. What looks good on your meters may not sound great on a different playback device.
b) Don’t over-compress! This is as much of iTunes request as it is my own. If you squash it too hard, you will kill it!
c) The ACC encoder has a great frequency response. However, rolling off the very top end a few db can work wonders for the compressed sound. Try rolling off at 16k and above and reviewing with the encoding material. This can be a big help!
Please contact andy@audiobaymastering.com with any questions.