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theproaudiofiles.com
The 2014 Mastering Guide to Audio
Formats and Delivery Mediums
Justin Perkins
Hi, I’m Justin Perkins of Mystery Room Mastering.
After writing different variations of the same email to clients over the
years about what formats they need for final masters, I thought it
was time put together a resource to cover as many bases as
possible.
There is much more to mastering than just the sonic aspects and it
varies between different release formats. It’s also gotten more
complex as digital distribution evolves, CDs become the minority,
and vinyl makes a comeback.
I hope you find this guide useful. Feel free to share it, leave a
comment or get in touch with me if you have any questions!
iTunes (standard), Spotify, and other online stores —
16-bit/44.1k WAV files
From your mastering engineer, request WAV files directly from the
mastering session, that have never been on an audio CD. These
files will be submitted to an aggregator such as CD Baby,
Tunecore, or The Orchard, to distribute your music to a variety of
channels chosen by you.
Be aware that if proper headroom is not present, some loud
masters can clip or contain overs when converted from WAV to
AAC, MP3, and other compressed formats used by most online
stores. More info on this below.
Mastered For iTunes — 24-bit/96k, 88.2k, 48k, or 44.1k sample
rate WAV files
Some aggregators are now offering Mastered For iTunes versions
of releases. This means you can submit 24-bit WAV files at sample
rates higher than 44.1k to the iTunes Store.
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Mastered For iTunes is not a completely separate master — it’s
based on your main digital master with a few adjustments to
optimize for the iTunes Store AAC format. The master files must
follow other guidelines specified by Apple that certified “Mastered
For iTunes” mastering studios are aware of.
You must use an approved Mastered For iTunes mastering studio in
order to be eligible for an official Mastered For iTunes release. You
may have to setup and pay for a separate Mastered For iTunes
version of your release. Check with your online
distributor/aggregator for specific details.
Bandcamp and SoundCloud — 24-bit WAV files (sample rates
above 44.1k)
Files uploaded to Bandcamp and SoundCloud can be 24-bit, and a
higher sampler rate than 44.1k if available from the mastering
engineer, which could make for better sound quality on the resulting
compressed files such as MP3s.
You can allow users to download your original higher resolution
masters, or compressed MP3s of smaller size.
Be aware of possible clipping and overs that can occur after
conversion by these websites and services to MP3 and other
compressed formats. More info on this below.
Compact Disc — DDP image or audio CD-R master
A DDP image is the best, quickest, and easiest to work with from a
mastering engineer’s standpoint. A DDP master can be easily sent
via Internet, but some small duplication orders may require a
physical audio CD-R master.
A CD-R master is ideally burned by your mastering engineer and
tested for burn/write errors before shipping to the CD manufacturer.
Check with your CD manufacturer to see if DDP works for them, or
if a physical CD-R master is needed. More info on DDP is found
below.
Vinyl — 24-bit WAV files (sample rates higher than 44.1k if
available)
The WAV files for your vinyl pre-master can be at the native sample
rate of your original mixes and/or mastering session (meaning
higher than 44.1k/CD quality).
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Creating a single WAV for each side of the record will ensure that
no changes with the space and timing between songs can occur at
the lacquer cutting stage. Sonic adjustments are often made to
optimize for the vinyl format before sending it off the pressing plant
or lacquer cutter. This can make or break the sound quality of your
vinyl.
Your original mastering engineer should be familiar with how to
optimize the audio of your vinyl pre-master for lacquer cutting. If
not, finding a mastering engineer that has this experience would be
beneficial.
There are a lot of variables related to vinyl audio quality, so working
with engineers familiar with the process is highly recommended.
Cassette — 16-bit WAV files (sample rates higher than 44.1k in
some cases)
The WAV files for your cassette pre-master can be at the native
sample rate of your original mastering session if accepted by the
cassette manufacturer.
Creating a single WAV for each side of the cassette (or “program”)
will help ensure that no changes with the space and timing between
songs can occur. You may wish to optimize audio for the cassette
format, as it may not need to be as loud and compressed, and
sibilance can be an issue with certain types of tape.
Check with the manufacturer for their specs.
Download Cards — MP3 (or whatever you want users to
download)
This is one situation where MP3 files are usually welcomed when it
comes to delivering your masters.
Most download card services simply host the files you upload to
them, and don’t do any further conversions or data compression.
Check your service for specifics.
Music Licensing — 16-bit/48k WAV files (with 320kbps
reference MP3)
The proper format needed for licensing your music will ultimately
depend on who licenses the music, and how you plan to distribute
it. However, the most common audio format for video use is
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16-bit/48k WAV.
Although the audio can be resampled down the line as needed, if
you’re serious about submitting your music to be licensed in video
productions you’ll want to ask your mastering engineer for
16-bit/48k WAV versions of your masters. This is especially true if
you’ve mastered instrumental versions of your songs, which most
commonly get licensed.
Acquiring 16-bit/48k versions of your masters and instrumentals
from your mastering engineer should ensure the best sound quality
as the audio is less likely to be resampled or converted down the
line, potentially with subpar sample rate conversion software.
It’s also useful to have reference MP3s of your instrumentals for
easy sending and auditioning by potential licensing clients and
users.
Exceptions and Notes
Always start with the highest resolution file available and
acceptable for the format in which you are distributing your music.
Up-Sampling a 44.1k WAV file to 96k does not add any quality to
your file. Converting an MP3 to WAV does not “add the resolution
back”. Once a file is reduced or down-converted, you must go back
to the source to retain the quality of your original master.
You should not convert MP3s into WAV files in order for them to be
used for online distribution. Once a WAV file has been reduced to
MP3 or AAC, the integrity and sound quality is gone forever. An
MP3 is to audio, as a grainy, pixilated image is to photography.
Once the data is stripped from a high resolution file, it cannot be
brought back. Even though you can technically make an MP3 into a
WAV file, you will still have a loss in quality compared to the original
WAV file. This loss of quality is particularly noticeable in the high
frequencies, resulting in a swirly, underwater sound depending on
the size and bit-rate of the mp3.
Even if you don’t notice these artifacts on well encoded MP3 or
AAC files, you will certainly notice problems when the MP3 or AAC
file you converted to WAV gets converted back to MP3 or AAC
again by Bandcamp, SoundCloud, or the iTunes Store.
The same is true regarding 24 and 16-bit files. Once a file is
reduced to 16-bit, it can’t be successfully converted back to 24-bit.
The missing bits are gone for good unless you revisit the original
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24-bit versions again.
File Tagging and Online Distribution
WAV & AIFF files don’t support the large amount of metadata that
an MP3 or AAC file can contain. If your mastering engineer
provides WAV files for uploading to online distribution services,
expect to submit the artwork and other metadata separately as you
submit the audio files for online distribution. The distribution service
you use will handle the metadata tagging that is seen by the end
user based on the info you enter, and what is supported by the end
file format.
When you purchase a song on the iTunes store for example, it is
delivered to you as an AAC file (also called MPEG-4) which is
considered a compressed file format similar to an MP3 but the AAC
file is generated from a 16-bit/44.1k WAV file.
Each individual store and streaming service has it’s own file specs
for files that the end user purchases or streams from any given
service, but they are all usually generated from the same
16-bit/44.1k WAV file that you submit to your aggregator. With most
aggregators, you can choose to distribute your music via iTunes
Store, Amazon, Google Play, Spotify, Rdio, and the list keeps
growing. There’s no reasonable way to optimize your audio
uniquely for them all, but you can take care to be sure your
mastered WAVs are optimized for the main stores which should
translate well to nearly all.
Some popular aggregators in the US are The Orchard, CD Baby,
and Tunecore. You upload your audio files and project details to the
aggregator just one time, and they take care of the details
regarding getting your music into the distribution channels you
choose.
DDP (Disc Description Protocol)
A DDP image is basically a digital image of a compact disc that
contains all the audio, track IDs, CD-Text, and ISRC codes.
DDP is not prone to the same errors that can occur with
phsyical CDs and CD-Rs such as skips, scratches, and read/write
errors. This is in part why it’s best to use a DDP image for your CD
production master rather than a physical CD-R.
Most professional mastering software can export a mastered
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project to DDP format. The DDP can be sent in for CD production
online, either by uploading to the website/FTP of the CD
manufacturer, or by providing a direct download link to your sales
person.
DDP is also useful for auditioning a final master to be sure you’re
hearing the exact sound quality, and song & track sequencing as
intended by the mastering engineer. It rules out any errors that can
occur when working with individual WAV files, and manually
assembling them in iTunes or other audio software. Most audio
playback and CD burning software programs have settings for
adding extra space between tracks, and some programs have
settings that can alter the sound quality and overall levels which
can be easy for users to overlook, resulting in an inaccurate
listening experience.
It is not recommended to submit individual WAV files for CD
production. This can lead to problems with song sequencing,
incorrect CD-Text, lack of CD-Text, and in some cases the audio
itself can be altered if files are handled improperly.
It’s easy these days for mastering studios and engineers to provide
a complimentary DDP Player with a DDP master in order for clients
audition and approve a master. This is ideal because the listener
will be listening to the exact same file that would be used for CD
replication and most online distribution services as of now. HOFA
makes a DDP Player that can be purchased for $9.99 (USD) which
is suggested if the mastering engineer can only supply a DDP
image, but not a player for you to audition the DDP. DDP is
especially useful when the mastering engineer and client are not in
the same location because a DDP file can be transmitted via
Internet quite easily.
ISRC Codes
An ISRC code is a digital fingerprint for each of your songs that
helps keep track of airplay and other ways your music can generate
royalties and credits. ISRC codes are not essential for CD and vinyl
releases, but your songs will need ISRC codes in order to be sold
on the iTunes Store, as well as most other online distribution
channels.
Some aggregators can generate ISRC codes for you if needed
when you setup online distribution. However, if you are also doing a
CD release, you may want to have the ISRC codes generated
before finalizing your CD master so the codes can also exist on the
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physical CDs.
Some mastering studios offer ISRC code generation, and you can
apply via the ISRC website to generate your own ISRC codes if you
prefer. Fees may apply depending on your method of operation.
Vinyl & Cassette
Ideally, your vinyl pre-master is one WAV file for each side, at the
native sample rate of your mixing and mastering sessions. Some
vinyl and cassette manufacturers may request that your audio
masters be sent on an audio CD-R.
Audio CD-R is limited to 16-bit/44.1k sample rate, and is generally
not a good way to submit, transfer, or store a master. Only use an
audio CD-R for a master if absolutely necessary due to
manufacturer limitations.
It’s recommended to use a manufacturer that can work directly with
your 24-bit/native sample rate WAV files for vinyl projects.
16-bit/native sample rate WAV files are usually ideal for cassette
duplication but your manufacturer may have specific requests and
specifications.
Vinyl Projects
Using a third party lacquer cutter can improve your final product
greatly.
Lacquer cutting is the first and arguably the most important step in
the vinyl process after your master leaves the original mastering
studio. You typically have a more open line of communication with a
third party lacquer cutter versus an in-house lacquer cutter at a
pressing plant. This is a big reason of why results are typically
better when using a third party lacquer cutter. It’s also much
cheaper and quicker to fix issues with your vinyl pre-master at the
lacquer cutting stage rather than at the test pressing stage if
problems arise.
Typically, when working directly with a pressing plant for your entire
vinyl order, you don’t get to hear anything until the test pressing is
ready, which is essentially the last third of the vinyl process. This
means that any fixes will likely require major back tracking and
could be costly and delay your order. When using a third party
lacquer cutter, once you approve the reference lacquer, the
production lacquer(s) are shipped off to the pressing plant of your
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choice for the remainder of the process, possibly with a stop in
between for metal plating depending on who you are working with
for the actual pressing.
Using a “one-stop shop” or broker for vinyl can certainly be easier
and less overwhelming, but you tend to see a wider variety of audio
quality depending on who you choose to work with. If using a
broker for a vinyl order, it doesn’t hurt to ask who is doing the
lacquer cutting to be sure they are using one of good quality.
You will also want to be aware of how long your sides are for vinyl
releases. Depending on the size of the record (7”, 10”, or 12”), and
the speed (RPM), you will be limited to how long each side can be
before the sound quality starts to be compromised.
With vinyl, there are no hard time limits like with a compact disc.
Each pressing plant and lacquer cutter has their own suggested
maximum times for sides, but generally speaking, sides will sound
better the shorter they are, and short sides can usually be cut
louder than long sides. Long sides are susceptible to distortion
(inner groove distortion), graininess near the end of the sides, and
the overall level of the sides will likely be quiet. Some manufactures
will not guarantee sound quality after exceeding a certain time.
For the vinyl pre-master, it may be worth removing songs from your
album, or shortening some songs to avoid long sides. The longest
side usually sets the level and tone of the record, so creating the
shortest, most even sides will produce the best results in most
cases.
Skilled lacquer cutters can sometimes produce good sounding
records at long lengths, but the results usually vary depending on
the source material and person doing the work. These maximum
times for sides are posted for a reason and should be taken
seriously if you care about the sound quality of your vinyl.
Mastered For iTunes
Only mastering studios that have been certified are allowed to
provide masters for Mastered For iTunes releases. What Mastered
For iTunes means is that you are submitting your mastered WAV
files to the iTunes Store at 24-bit, and the highest sample rate
available for your project.
Up-sampling a 44.1k/16-bit master to 96k/24-bit will not be
beneficial, but if your mastering engineer can provide high sample
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rate, 24-bit masters, it’s something to be ready for when Apple
opens up the Mastered For iTunes program up to all artists —
hopefully in the near future.
The other important step in the Mastered For iTunes process is that
the master is auditioned through a special encoder to be sure that
your masters will not clip or contain overs when they are converted
to AAC for distribution in the iTunes store. Without leaving the
proper amount of headroom on loud digital masters (as most are
these days), it’s fairly easy for clipping or overs to occur when your
loud mastered WAV files are converted to AAC or other
compressed formats such as MP3.
The severity of the clipping that occurs depends on the material,
how loud it’s mastered, and other variables controlled by the
mastering engineer. This is why careful testing must take place for
each song within each project to qualify as Mastered For iTunes
compatible. Every second of every song must be analyzed through
the encoder to test for overs and the proper headroom must be set
to avoid these overs throughout the course of the song, or complete
album.
The most common method to prevent clipping and overs when your
mastered WAV files are converted to a compressed format, is
lowering the output ceiling of the final limiter in the mastering
session to a certain point in order to leave enough headroom for
the file conversion and data compression process.
Back when CDs were the main digital format, the standard setting
for a digital limiter’s output ceiling was -0.2, to prevent distortion
within cheaper CD players and playback components. It was
eventually discovered that -0.2 dB is not enough headroom to
prevent clipping when loud masters are converted to compressed
formats such as MP3 and AAC. It’s becoming more popular to
lower the final limiter output ceiling as low as -1.0 dB to prevent
clipping and overs when the file is converted to a compressed
format. Again, the actual clipping instances will depend on the
variables of the material and how it’s mastered. Typically, you want
to lower your output ceiling as little as needed, but just enough to
prevent these overs when converted to MP3 or AAC.
The optimal setting is dependent on your specific material and the
target compressed format. Lower quality MP3s tend to clip more
easily than higher quality mp3s.
There are a variety of tools that a mastering engineer can use to
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know how a master will react to a certain MP3 or AAC encoding.
Some popular options are Sonnox Fraunhofer Pro-Codec, Sonnox
Codec Toolbox, the Encoder Checker that is now built into Wavelab
8.5, as well as tools and droplets provided for free by Apple.
However, the tools provided by Apple are Mac/OS X only. The
Sonnox encoder testers are plugins in VST, AAX, RTAS, and AU
formats so they can run within a number of audio software
applications on both Windows and Mac OSX. Sonnox Codec
Toolbox has standalone version as well that can run on it’s own
outside of any other audio software.
Even if you do not wish to do an official Mastered For iTunes
release, it doesn’t hurt to comply with as many of the guidelines as
possible. Even if you only choose to submit 16- bit/44.1k WAV files
to your iTunes aggregators, you can still have your mastering
engineer be sure that there is enough headroom in the WAV files
you submit to avoid clipping and overs. This can result in a more
pleasing sounding file for the end user that purchases your music
via iTunes, as well as other stores and streaming services.
Other Channels
The Mastered For iTunes theory can be applied to most of the
online distribution channels as well. However, it’s not always clear
what format your WAV file gets converted to after you upload it,
depending on the distribution channel, nor is there a way to test
exclusively for all the various encoders your music could encounter.
It’s important to communicate to your mastering engineer, how and
where you plan to distribute your music, and read the fine print on
the file specifications for any given distribution service.
Metadata
If you’re wondering why iTunes or other music playback software
on your computer will not recognize song titles, artist name, album
name, cover art and other info when you insert your audio CD, it’s
because your audio CD is not registered with the Gracenote
database (for iTunes support) and/or All Music (for Windows Media
Player support).
It’s also possible for iTunes to believe your CD is of another artist if
the total track numbers and times happen to match, which is more
common with CDs with lower track totals.
CD-Text
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The information embedded on your audio CD (self-burned,
duplicated, or professionally replicated) is called CD-Text, and can
only be displayed by CD players that support CD-Text. This usually
includes car stereos and high-end home CD players. Most music
playback software such as iTunes, Windows Media Player and
Winamp can’t read or display the CD-Text embedded on your audio
CD.
Because of the way Gracenote and All Music databases work, your
computer needs to be connected to the Internet to match and
retrieve data for any given audio CD that is inserted. For example,
even if you insert a popular CD that is registered with the
databases into your computer, it will only automatically retrieve the
CD info if the computer is connected to the Internet. It is not
currently possible to embed the artwork or any other metadata info
directly onto a burned audio CD or the production master for your
CD. CD-Text and Gracenote and All Music metadata are two
separate things.
Until the CD’s info is submitted to Gracenote and All Music, your
computer’s software will only read the songs/tracks as Track 01,
Track 02, etc. This is normal.
The way that Gracenote and All Music identify an audio CD is by
analyzing the number of tracks, their exact lengths, and finding a
match in their database. This is why it’s not uncommon to see a few
possible matches when you insert a CD with only a few tracks. The
odds of the number of tracks and their lengths matching an existing
CD are much greater for CDs with few tracks. It’s important to wait
until you have a final master to submit the info to Gracenote and All
Music, as sometimes track lengths can change slightly throughout
the mastering process as changes are made.
Once you have a final master, you can submit the info to Gracenote
online.
Submissions to All Music must be done by mailing them a physical
copy of your CD. More info here.
Once the info is submitted, it can take roughly 48 hours to be active
via Gracenote, and 4-6 weeks for All Music (Windows Media
Player).
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