When confronted with the task of 'mastering' a track its essence lies in making it 'fit for purpose' i.e. sounding great on all play back systems. However, many engineers get bogged down in a quest for perceived loudness. Which to be fair on many occasions is naively directed from the desire to 'sound as loud as ...' the latest commercial release.
In my personal journey of audio development and teaching over many years, I've found the most positive way to start engaging capable engineers in their comprehension of the issues of loudness is to discuss the concept of 'The Cube'.
So how do we achieve this anticipated goal of volume without the side effects?
When first listening to a session mix we're hearing tens, if not hundreds, of hours of hard work from an artistic and engineering point of view. These efforts should not be ignored, but become the intrinsic focus for the improvement of a product. We, as the mastering engineer, are there to reinforce the positive work already engaged in, not to try to remix or re-engineer the supplied audio.
This focus is important when we are trying to sit back from a mix and not hear the details but the overall hue of a track – its tonal integrity, micro, macro dynamics and especially width. In seeking the correct end game we must first absorb a mix's virtue. Remembering at all times we are mastering not mixing!
In a quest for perceived loudness it's not through the use of limiting but that of excellent tonal, dynamic and spatial balance. A limiter may be applied as a final process to capture peaks with minimal artefacts on the audio, not pushing down / pumping / distorting to achieve more gain reduction – hence perceived volume.
This principle of excellent tonal and dynamic balance focused on the RMS of a signal and not it's digital peak is the essence of all good masters throughout the history of modern music.
With this concept in mind, imagine a cube of equal dimensions containing audio as if it has frequency is from top to bottom, panorama from left to right and depth of field from front to back.
Visualise a session mix inside the cube. The cube is a finite space limited by resolution of the audio transfer path and the session mix does not occupy all the space. It could have too much lower mid or bass – these could be poking dynamically out of the front of the cube but the average is within the space. Bass runs from left to right as well as front to back. The middle pushes across the dimensions but does not dynamically sit balanced within the 'cube' and so on.
Remember the cube is balance / perfection – an ideal we are trying to achieve. Often the session mix will be outside, unbalanced from this 'ideal' – the point of mastering is to fit to this uniformity of balance, thus translate on all playback systems and be 'fit for purpose'.
Using this thought process it becomes quite clear any session mix does not occupy all this space. This is normal, a mix is a balance of many parts and details over time, a master is an overview of tone and dynamic over time. It would be highly unusual for a mix to sound 'mastered' as this stage but not unheard of.
Filling the cube
If we simply try to use a limiter to control the dynamics to achieve perceived loudness, without first addressing balance issues, the limiter can only push so far before the density of unbalanced signal makes the gain reduction pump or distort. Especially as the directives for frequency are not spread but focused with in the mix.
If when mastering we can focus on pushing the mix into all the extremities of this cube, making it occupy all of the available space, it becomes obvious how much less 'limiting' is required to achieve a 'perceived' level of loudness. It's already occupying all the frequency balance, pan and depth of field. Hence – inherently louder by its better relationship between frequency of RMS to peak.
If we can occupy all the dimensions of 'the cube' in all the aspect of frequency and depth and width it becomes clear why 'excellent' songs have an inherent ability to translate on to any playback system.
These types of tracks should be added to the best reference tracks you'll ever find personally. Something that sounds great on a beach bar in Thailand or a Club in New York – on the bus on somebody else's phone the row behind – basically anywhere. Great sounding masters should translate to all environments.
This is not a discussion on genre or style or a music's medium for 'correct' playback. This just simplifies the concept that if we try to make our masters occupy all these dimensions it will inherently translate.
The inline of treble
Another interesting way to start to 'hear' the cube is to just focus on the treble. When listening to great music / masters you'll notice the treble / air always sounds even across the left to centre to right – a straight line. No dip or roll off / boost. A clump at any point will lead inevitability to a reduction on perceived loudness in a track and its ability to translate effectively on to all systems.
In conclusion, and speaking as someone who is the supporter of a mastering grade high resolution download store (www.fdrhd.com), I see no rational for restricting the dynamic range past that of the optimal, except for the argument of listening environment. If you're listening in a car you'll need a more dynamically restrained master than that of the perfect home theatre environment.
This means loudness is important, but as engineer we should not compromise the need to make a song loud as opposed to great in its musical and engineering integrity, as is possible in the hands of a skilled mastering engineer. It will sound as loud as the rest because they've occupied the 'cube' but importantly not suffer the artefacts of poor limiting evident on so many releases to date.