I felt compelled to write about mastering audio for 2014 and onwards. Of late, there have been developments which suggest file formats and music distribution channels are likely to evolve over the forthcoming years, and as such you need to have some basic information about these changes.
Historically, mastering has been a final production service with multiple goals before the music is released. One of those goals has been multiple release formats, such as CD, vinyl and cassette.
More recently, the files for a CD release and the digital (online) release have often been one and the same—typically a 16 bit .wav, or .aiff uncompressed PCM file. So the file used to create the master CD has often doubled up as the digital online version.
This is not exclusively the case, but is certainly my own experience, and seems to be how most online distribution has been geared up for over the last five years.
How We Arrived Where We Are
In tandem with single-master creation, the loudness wars have constantly pumped up the perceived volumes of music releases over the last decade or so. One loud master has become the norm for some music genres, whether it is for CD or digital online release.
With anything related to mastering, it is not wise to generalise. It is, after all, a bespoke service. Some genres that benefit from wide dynamic range have largely been exempt from taking part in the so-called loudness war. I would say dance, pop, rock, R'n'B and hip hop music in its various forms are probably the genres that have followed the trend of increases in perceived volumes. Jazz, country, acoustic, folk and classical have suffered less.
For those in it to win the "loudness race", the continual improvement of digital limiters have allowed higher and higher perceived volumes, with fewer side effects. Of course, there are multiple methods to achieve loud end results, but the limiter is ubiquitous in loud mastering. In short, the modern look-ahead limiter is capable of relatively transparently arresting amplitude peaks in a music mix, therefore creating a higher average level to the human ears.
Rightly or wrongly, this has been the case. The often-cited reasoning is that a band, musician or label fears that their track will be quieter than the one played before or after. This situation is understandable, especially in a nightclub/DJ setting, or a publisher/radio commissioning round. Sadly, many DJs are no longer pre-fade cueing the incoming track and adjusting gains so the volumes match.
No one can deny the damage to transients, punch, depth, space, clarity, detail, dynamics and musical involvement that high perceived volumes have done to some music genres over the years. Extremely loud masters do not tend to fare well from the perspective of fidelity when broadcast on FM radio, and when converted to compressed audio file formats.
There Are Signs of Change to Come
There are currently some interesting developments that indicate multiple release files may once again be a prudent move. At this time, the goal of mastering is to be a well-judged, multi-facetted compromise that lives within the aperture of best translation across many different sound systems and formats.
Car stereos, FM stereo/mono broadcasts, online compressed formats, in-store, iPods, smartphones, multimedia speakers, and audiophile hi-fi systems may all be used to play your music. The goalposts for how this judgement is being made is moving.
This is important, and whilst there is no certainty in what might eventually happen, it makes sense to discuss the possibilities and changes coming. The main changes as I see it are as follows and yet distinct from each other in their goals:
- 1. The Mastered for iTunes program
- 2. Volume normalisation systems.
The Mastered for iTunes requirements involve very specific tweaks during mastering, and some post-production compliance work. In short, Apple is attempting to ensure the best possible fidelity from their lossy 256kbps AAC encoding algorithm. In addition they will store a high quality version of your file in their archives.
The guidelines recommend more headroom than most masters have been created with, and that the files should be a minimum of 24-bit in resolution, and at least 44.1kHz in sample rate. Higher sample rates are encouraged.
I recommend reading the Apple guidelines for mastering engineers even if you only work semi-professionally, and perform DIY self-finalising, as it is indeed a development worth knowing about.
As a mastering engineer, I am occasionally posed the question, "Will these masters be OK for iTunes?" The answer to this question is that unless a mastering job has been specifically requested as being "MFiT compliant", the tracks will not typically be mastered with those very specific guidelines. If the client is asking if the masters will be accepted by Apple for upload to iTunes, they of course will. However they cannot be submitted or marketed as specifically "Mastered for iTunes".
If this is of interest to you, as an independent artist or small label, you should ensure that your distributor can accept high resolution files. At the time of writing, quite a few online distribution companies are not geared up to accept audio of greater resolution that 16bit/44.1kHz. So before you request tracks to be mastered to MFiT specification, you should enquire with your chosen online distributor if they can accept higher resolution files or not.
In addition, you should enquire as to whether or not there are any additional fees for submitting more than one set of mastered files. This may be applicable whether you are going it alone or employing a professional mastering engineer for your project. So it may have budgetary considerations as well as sonic considerations.
2. Media Player Volume Normalisation
Currently, some media players and proprietary streaming interfaces have an option to check a box to "Play all files at same volume," or something similarly worded. Currently these are optional, but some streaming services may switch their volume normalisation options on in software by default in the future.
These systems work a little differently to each other, but they amount to tagging each piece of music with information that cues the media player to attenuate or increase internal playback volume, depending on how loud the sensing algorithm believes a track is.
We will have to wait and see. Although not officially announced, it appears that iTunes Radio (at time of writing available in the US only) has a version of Soundcheck switched on, which as a radio service would make a lot of sense. If not Soundcheck specifically, then some similar volume normalising system.
It is worth mentioning that FM broadcasters have a type of volume normalisation, in that they multiband compress and limit the music they broadcast. Of course this dynamic control is much more drastic than mere volume balancing, but for such services and playlists it at least demonstrates the use of some kind of perceived volume management. After all, constantly changing volumes is annoying for the vast majority of listeners.
What Does This Mean When Mastering Music?
If we produce one loud master, these tracks will be pushed down in level due to volume normalisation. Everyone's music will play back at approximately the same volume, irrelevant to whether your music tracks average -16dB RMS or -5dB RMS. So loud tracks will simply be pushed down in volume in compressed file format form.
If these changes do occur, and slowly find their way into more and more media consumption outlets, we will find that this means that loudness maximisation may eventually begin to be less important. These algorithms are quite sophisticated at calculating the perceived volume of the tracks.
However, even if these volume normalisation systems are taken up on multiple media players/streaming services and online radio globally, we could assert that limiting may remain for two main reasons:
- For imparting a limited sonic character to music. Heavily limited music tends to have what can be described as "pressure", which can work for some "shock and awe" musical styles, and it may to a degree have become part of the actual sonic signature of these music genres.
- Loud versions may still apply for CD releases and club situations, as well as independently streamed files, for example, from an artist's website.
Currently the situation is ambiguous and dependent on specific situations, but it makes a lot of sense to consider the various situations in which your music may be heard for both promotional purposes and actual release. In any event, the perceived volume—be it high or low—is likely to become a more important factor to consider as time moves on.
As such, musicians and record labels have to make open-minded decisions about the perceived volumes and formats that they should request at the mastering stage. It would be prudent to ensure that all bases are covered.
Mastering for iTunes is a personal choice for a band, musician or record label. It may relate to budget and perceived audibility of improved fidelity, and whether chosen distribution channels can accept high resolution files. It is a free choice for the individuals concerned.
Choice of formats required should be considered in depth when you start DIY finalizing, or when you choose professional mastering services.
What Specific Files and Formats Should Be Requested at Mastering Time?
The following information is given on the basis that every mastering job, whether it is performed as a DIY self-finalised job or a professional mastering job, is unique in its goals.
Firstly, I recommend you look into a meter that is capable of measuring loudness units (LU) below full scale (LUFS for short, also known as LKFS - Loudness K-Weighted Full Scale). This metering system provides a new average loudness reading which more accurately bridges the common disparity between what is measured and what a human hears.
Digital metering in the past has not correlated well with the perceived volume to human ears. Two very different pieces of music could read similarly on a digital peak meter, and yet have rather different perceived volumes to the ear. Some modern sequencers ship with an LUFS meter and you can find third party plug-ins as well.
It has been reported that iTunes Radio seems to play music at around -16.5LUFS. This would mean that music at this level would not be subject to large volume manipulations either upwards or downwards. At this level you are likely to have a fairly dynamic master with all transients, clarity, depth and space unrestrained by limiting. By not limiting the track, the mix can retain punch, depth, detail and power that is easily lost with excessive limiting, and yet is played out at roughly equal volume as other tracks.
In my opinion as a professional mastering engineer, it's currently prudent for musicians to request (or create) at the very least a 24-bit unlimited master, as well as any "loud" versions. This would include any equalisation, compression (and other dynamic processing), stereo image manipulations, characterful processing etc. This unrestrained dynamics version (if this is what you choose sonically) would sound good on volume-normalised playback systems.
Or rather non-conclusion—we cannot conclude this complex topic because these changes are in flux and subject to wider music industry uptake. It is too early to say if, how, who and when these changes may be implemented. What is sure, is that making a lower-level 24-bit version (probably at around -16LUFS) in preparation is a good plan, especially for artists whose music is being sold today and not used for purely promotional purposes.
It is early days, and neither guarantees nor predictions can be made with any certainty, so it's a good plan to ensure you cover as many options as possible (relative to your budget), until we can all see where the music industry ends up on this issue. As we know, the music industry is quite fragmented, and it can take quite a while to respond to new technology, ideas and changes.
Hopefully this article inspires thought about your music production, files, volumes and mastering, and helps you prepare for new developments. I for one embrace these new developments, as I believe that lower perceived levels will potentially allow high-end mastering equipment to show what it is truly capable of, without being masked by digital distortion and other extreme dynamic processing side effects. I look forward to being able to listen to high-resolution formats in the future that are truly "audiophile" in nature—detailed, clear, and communicating exactly what the artists wanted to.
Yes, it is ambiguous at the time of writing, and there is a lot of education, system changes, and industry-wide sharing of knowledge still to happen, but I cautiously believe it is heading in the right direction for the betterment of musical fidelity.
Article supplied by Push Mastering.