Brief Summary
If a mix is lacking depth, the solution might be to move supporting instruments and mix elements back in the mix rather than try to bring the principal elements forward. Having a good understanding of depth cues really helps. What makes sounds sound distant anyway?
Going Deeper
When it comes to mixing music, an often overlooked aspect is achieving a sense of depth and perspective. The desire to make sounds stand out, to be ‘in your face’ can obscure the fact that if everything is front and centre, the mix will inevitably be one-dimensional!
Creating a sonic landscape requires more than just balancing levels and panning instruments. Attention also has to be paid to the spatial characteristics of each element, from the front of the mix to its deepest recesses. This article explores techniques to introduce or heighten front to back depth and perspective in your mixes.
Contrast
How do you make something loud? By surrounding it with quiet. Drop a book in a busy airport and it makes no impression, do the same in a library… I’m sure you get my point!
Exactly the same applies to front to back perspective and if you want to make something sound close, the most effective way to achieve this isn’t to make a close sound sound closer, it is to make the other sounds around it sound further away. If you are capturing sounds in a real space then the best way to do this is to place microphones in a way which captures these spatial relationships. There’s nothing like the real thing.
However, recorded music so often doesn’t present sounds as they exist in nature and in the same way as we manipulate the left-right panorama in a stereo mix using a pan pot, we sometimes want to manipulate front to back perspective. The only thing is there isn’t a mixer pot for that.
Our distance perception is particularly acute as sounds get close enough that you would be able to to reach out and touch them. This is more correctly referred to as peripersonal space, meaning within approximately one metre of the listener, as opposed to extrapersonal space beyond one metre. The significance of close sounds is that they represent potential immediate threat so sounds which carry the auditory cues which identify them as close to the listener attract immediate attention, literally attention-grabbing!
So to place sounds further from or closer to us we have to identify the cues which our brains interpret to identify distance and fake them in the mix. So what are they?
Level
We’re extremely good at interpreting the effect increasing distance has on level. The Inverse Square Law describes the relationship between distance and level and it’s not hard to understand. If sound can radiate in all directions equally the energy is distributed over a larger and larger area. While distance increases in one direction only, the area over which the sound is stretched increases in two.
This is useful because it is so fundamental to our understanding of how sound works. The real world level of many sounds is arbitrary, A synth patch carries no information about how loud it ought to be, but a snare drum rimshot or a fortissimo French horn is recognisably loud. Making it quieter in the mix implies distance, though without some other associated cues it’s unlikely to sound natural. But before adding other cues it’s helpful to consider the role of level in placing sounds front to back.
Brightness
Air is a viscous fluid, this means it is slightly sticky, and this stickiness affects how it absorbs sound energy passing through it. Anyone who has ever heard thunder from a distance compared to lightning from close quarters will appreciate how this absorption affects high frequencies more than lower ones. Rolling off high frequencies is one of the principal auditory cues for distance. Dialling in a low pass filter gets you some of the way there but the effect isn’t as simple as a conventional filter slope. The reasons are complex and the viscosity varies with both temperature and humidity and rolls off with increasing steepness as frequency rises.
For post production use the distances mixers are seeking to fake can be considerable and at these distances the roll off can be severe but as the distances involved in a music performance are relatively minor this HF roll off will be subtle. A combination of a shallow high shelf cut relatively low down followed by a low pass filter much higher up will suffice but if you need a truly accurate reproduction of this effect Sound Particles make a plugin called Air which reproduces the effect for post production use.
Width
Not all sound sources have appreciable width. A vocal for example is effectively a point source. A drum kit or a piano span a couple of metres and if you wish to present either of these as being at a distance from the listener the width needs to decrease accordingly. At any significant distance they will quickly be not much wider than a point source. An application where this stereo angle will be particularly relevant is placing larger ensembles. A string section or choir will benefit from some narrowing if you are trying to push it back in the mix. However to be convincing it will be much easier with appropriate use of reverb. While the dry width of sounds narrows with distance, reverb stays wide.
Direct To Reflected Sound
We are very attuned as listeners to the contribution reverb makes to our distance perception. The closer we are to a sound source the more direct sound we hear relative to reflected sound. The proportion of reflected sound increases with distance until we reach a point called the ‘critical distance’ at which the level of reflected sound is equal to the level of direct sound. With further increased distance the level of reflected sound exceeds the direct sound and intelligibility suffers with the dominance of sound which is smeared in the time domain due to the multiple paths it has taken to our ears.
Things are more complicated that that though as at moderate distance the reflected sound is dominated by early reflections. Multiple discrete reflections which carry very specific information about the shape and character of the acoustic space. Beyond the critical distance late reflections begin to dominate, these are too densely spaced to carry much specific information but are still very important.
It’s true that adding reverb makes things sound more distant but actually, being more specific in how you treat sounds can help achieve better results. Extra room reflections are ideal for creating distance with very convincing placement in space. Using something like Liquidsonics’ Cinematic Rooms can create super-realistic acoustic cues. However, these cues can be very characterful and often a less specific reverb which doesn’t clash with the existing early reflections is what is called for. A neutral, uncoloured reverb tail from an algorithmic reverb without any early reflections added to a source can very effectively imply it is further back than it is.
Detail
A lot of time has been spent in this article describing the cues which make sound appear further away. What about bringing them closer? The issue with this is that so many sounds are captured using close mic techniques so they are already close. My first point about contrast was with this in mind because if a sound is already captured from an handful of inches away, how much closer can it get?
Increasing brightness can help, though this is potentially a case for multiband compression rather than static EQ. On the subject of compression, voiceless elements of a vocal in particular such as breath, mouth noises and such become more dominant when very close and using heavy compression to increase intimacy on vocals has been a common technique for years. A tool which is worth checking out if you want to manipulate the relationship between tonal and noise based elements of a vocal is Eventide’s Split EQ which offers more direct control over these elements than an EQ or a full or multiband compressor.
Mix In Context
An interesting closing point is to consider why a lack of front to back perspective exists in many stereo mixes. The overdubbed nature of many recordings, combined with the default choice of many to use a close cardioid mic means that sounds tend to be captured dry and close. If sounds are heavily processed and especially if choices are made in solo, without reference to how they sit with other instruments it becomes easy to see how a lack of contrast and perspective might occur. Considering pushing some sounds back so others can take the spotlight is an important step in creating a cohesive whole.