We spend a great deal of time considering individual sounds in a space. We prescribe attributes to the instruments and the players in order to organize our thoughts about the sounds and how they blend. We may often say a singer is “mid-rangy,” a snare is “ringy,” or perhaps the acoustic guitar is “warm.” We do the same for microphones, pre-amps, compressors, and what have you. It is surprising how little time is spent considering the sound of rooms, reverbs, delays, and whatever other spaces are coexisting within our mix. Considering that sound is defined by air vibrations within a space one would think the room would be held in equal importance to that which is resonating in it. But, when entering a new space, how often do we consider it’s sonic characteristics. And more frequently, when building a mix, how often do we think of space(s) as its own sonic element?
Perhaps more often than we realize. After all, why do we spend so much time rolling through reverb presets trying to find the perfect one – when we seldom know what the right one will be? And why does a plate sound good one time, but a hall sounds better next? Something instinctive is motivating these decisions. Like all sound sources, we are on some fundamental level listening for – and striving for – tone, rhythm, and coherence.
The purpose of having customizable reverb is to find that which perfectly compliments the sound source – or the surrounding sound sources. We can pick and choose a reverb with a certain sound that highlights the tones or rhythms in our mix. And frequently, we will send multiple sound sources to the same reverb for the sake of coherence.
The complication comes in when there are multiple spaces present in the mix. After all, how can one element exist in two spaces at once? Or three? or, why is it that the choir sounds like it’s in a church while the lead vocalist sounds like she/he is in a concert hall?
Sonic Cues for the Listener
Of course, the end listener is not listening on such a discerning level. The end listener is only picking up on subtle sonic cues that either indicate the sound is coherent or disjointed. So our task is to lead the listener’s ear where we want it to go. Do we want a unified sense of space, or something surreal?
That’s our job as the artist, producer, or engineer. To orchestrate all the sounds and consider what feelings and emotions they evoke. They key word here being “orchestrate.” A random piling of sounds will certainly sound “unmixed” or perhaps more importantly, “ineffective.” Reverb and space are no exception.
Listening for Spacial Characteristics
The primary goal to understanding and sussing out any mix is listening. When listening to the drums, bass, vocals, strings, etc, perhaps we should also make a point of listening to the space in the capture. If you’re not used to listening to space then using a compressor as a listening tool with a fast attack and release and a low threshold will exaggerate the room sound in the capture. Everything has spatial characteristics. A bass DI’d has no space sound – but that is still a spatial characteristic and must be considered. After all, if everything is close miked in isolation rooms, or DI’d, the capture is going to come out very dry, for better or worse (usually worse).
While listening to spacial sound, we are inherently listening to our front to back sound field. A DI’d bass is going to sound extremely forward while our drum kit miked from thirty feet away will naturally sound way back. This is a major advantage when organizing the image of our mix – as it can be recorded strategically to do the front to back work for us.
The trickier part of listening to space is the tonal cues. This is an immensely complex task, but can effectively be dumbed down into frequency response and “texture.” This can be broken down into an even more fundamental question: Are the room sounds complimenting each other or clashing? A bright, open, Lex PCM 96 Hall reverb might sound fantastic on vocals, but if the acoustic guitar was recorded in a dark sounding, dense room, the two reverb sounds will clash (or at least sound incoherent). While every mix is different, by and large this example will yield something that sounds “unmixed.”
Mix the Ambience
A brilliant colleague of mine named Gregory Scott turned me on to a unique but supremely effective concept. He said that one of the fastest ways to improve one’s mix is to “mix the ambience.” I’ve taken this to mean mixing not just with the space sound(s) in mind, but actually take the time to get all your room mics, reverbs, and delays up front or in group-solo and mix them. Get the plate slap from the snare sounding like it belongs with the room capture on the guitar. Or – if you have a surreal space – make sure it’s orchestrated in a way where the entire sense of space is working in the mix, or focus of the space moves in an evocative way (more on this in the next article). Once all the ambience tracks are mixed start bringing in the elements that have the most space in them – drum OHs, and mid-distant strings for example – and focus specifically on their space and how it sounds with the other spaces.
Tools for Mixing the Space
As with all facets of mixing and recording, the source sounds are paramount.
Choosing the best reverb(s) for the job up front will ultimately determine the end result. So, even before we get into the mixing of the space, let’s talk about sound selection. In a musical piece, we can treat the reverb as any other sound source, with four basic components:rhythm, volume, tone and texture.
One of the key elements of any reverb is it’s decay. The length of the tail is often an indication of the expanse of the space. However, it also determines the time in which the reflections sustain in the mix – and that’s a rhythmic concern.
A long sustaining sound in a fast tempo piece, or rhythmically complex piece is going to mask elements of the mix and generally slur the overall rhythm. A quickly decaying tail in a slow piece on the other hand, will leave a lot of empty space with very little impact from the reverb. Find a tail length that compliments the speed of the piece.
Another rhythmic consideration is the speed of the pre-delay. Pre-delay is a key element in determining the front to back relationship of the dry sound and the space it exists in. In other words, pre-delay helps the ear recognize how close or far the dry sound is. Generally speaking, the longer the pre-delay, the closer the dry sound. A zero millisecond pre-delay means that the reflections and the dry sound are reaching the ear simultaneously – which puts the dry sound far away. This acoustic phenomenon could be an article all to itself, but we’ll leave it at that for now.
Pre-delay is also a rhythmic element – it determines a space of time from the initial dry sound before the early reflections show up. Anything within the Haas Zone (10ms or less), isn’t going to have much effect on the rhythmic sense of the sound. Once you start getting up to 20ms and greater, the slap back effect becomes distinct and there is a clear rhythmic effect. Find a pre-delay that compliments the speed or rhythm of the piece.
Lastly, some reverbs (particularly room and hall style reverbs) have a rhythmic space between the early reflections and late reflections. This is not always controllable, but listening for that “bulky” moment in the reverb sound is very important when selecting a reverb. Often times, plates are a good choice for drums partially because there are no “early” or “late” reflections – eliminating that particular rhythmic concern.
Generally, when I’m mixing, I prefer just enough reverb to add a little life to the elements in the mix. Often, I’m setting my reverbs 15 or 20dbFS lower than my dry elements. However, this isn’t to say reverbs can’t come to the foreground. It’s a very important aesthetic decision. Just remember that whether the reverbs are subtle or prominent, they still need to sound right. Tone and Texture – this is where we get into the gritty stuff. There are many factors in determining the tone and texture of a reverb. First comes the style of the algorithm or convolution, then the three “D”s: diffusion, density, and damping.
Algorithms and Processors:
- Springs and Plates – A transducer sends vibrations across a metal coil, which are then picked up by another transducer. Springs have a “rigged” texture, and a hollow tone. Certain frequencies will jump more than others. Plates use a similar system, but work around vibrating metal plates. The result is a more natural sound – but one which is often “denser” than a real space. Plates will also highlight certain frequencies. The exact tonal qualities will vary to some degree in spring reverbs, and to a greater degree in plates. One major tonal difference is that plates tend to be “shinier” than springs, which feel more “empty” or “lonely” if those words can even apply to sound. Vibrations appear immediately and decay linearly – there are no early or late reflections. Because of these things, plates and springs are often very distinct and forward sounding reverbs, and useful for adding firmness or punch to the elements that feed them.
- Chambers, Halls and Rooms – Hall and room reverbs simulate the way a sound would actually acting in a given space. The characteristic sounds will change distinctly from unit to unit. Rooms are often based on rectangular or semi-rectangular, level spaces. Halls are often modeled off of minute amphitheater designs with curvature to the walls and incline from the sound source. Halls will usually have less separation between the early and late reflections. Otherwise, the algorithms are generally based around a size approximation. Halls are designed to be vast and deep. Rooms are designed to be natural. Halls will have a more even tone, whereas rooms may have resonant peaks and dips – but this is entirely dependent on the particular reverb unit. Chambers are unique room designs, and will vary as often as actual reverb chambers will vary.
Many reverbs, especially the “natural” space algorithms also may have settings for diffusion, density, and damping…
Diffusion is the scattering of the reflections. One can think of diffusion on a scale from “concentrated” to “open”. The interior of a big, empty oil drum would have almost no diffusion. The boundaries are smooth and evenly proportioned. Meanwhile, a dense forest would be extremely diffusive – all the reflection points are angular and rough and randomly proportioned to one another. Spaces tend to sound deeper when there is more diffusion, as echoes will scatter more each time they reflect off of the boundaries. Be aware that different reverb units will create a more diffuse sound when the diffusion is set higher, and some will create a less diffuse sound when the diffusion is set higher (confusing, right?).
Damping refers to the absorptive properties of the space. Damping is non-linear across the frequency spectrum. Every material has it’s own damping properties; however, most reverb processors allow at least some control over the high damping. Sheet rock and metal have very minimal damping, and tend to sound bright and ringy. Brick and wood have a medium amount of damping, often making for choice material for sound spaces. Rooms overly treated with absorptive materials such as fiberglass or acoustic foam have a great deal of damping and can often sound dark. Tone wise, damping will reflect how long the high end of the reverb stays present during the decay.
Density refers to the number of reflections over a given increment of time. Plates tend to be naturally dense as the actual resonance is very fast – whereas springs tend to be much less dense. Lower densities tend to reveal a “ripply” quality in the reverb – for better or worse – and these will be most apparent in short transient sounds (drums and anything played staccato).
This is definitely a lot of information to absorb (pun completely intended). Read, re-read, and play with different settings on your reverb units, and note the results.
Be discerning – the rhythmic, tonal, and textural choices are equivalent of choosing guitar amp settings or drum tunings. If chosen wisely, the mix will be easy, if not, you’re in for an uphill battle.