Pro Audio Files

The Importance of Space in a Mix: Part II

[If you haven’t already, read The Importance of Space in a Mix: Part 1]

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.

Rhythm

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 consideration.

A long sustaining sound in a fast tempo (or rhythmically complex) piece is going to mask elements of the mix and generally slur the overall rhythm.

A fast 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.

Pre-Delay

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 or more, the slap-back effect becomes distinct and there’s 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 important when selecting reverb.

Often times, plates are a good choice for drums, partially because there are no “early” or “late” reflections — eliminating that particular rhythmic concern.

Volume

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 20 dBFS 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.

Ronan C. Murphy | Reverb | ronansrecordingshow.com

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 “rigid” 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. Very 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 act 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 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 more 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

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 will 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 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

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 for 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 them a choice material in 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

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 this will be most apparent in short transient sounds (drums and anything else played staccato).

Conclusion

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 to choosing guitar amp settings or drum tunings.

If chosen wisely, the mix will be easy, if not, you’re in for an uphill battle.

Part 3 : Techniques for Mixing the Space…

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Matthew Weiss

Matthew Weiss

Matthew Weiss is a Grammy nominated and Spellemann Award winning audio engineer from Philadelphia. Matthew has mixed songs for Snoop, Sonny Digital, Gorilla Zoe, Uri Caine, Dizzee Rascal, Arrested Development, 9th Wonder, !llmind & more. Get in touch: Weiss-Sound.com.


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  • Rhekluse

    Great article. I’m surprised you didn’t touch up on Panning at all.

    • I’ve been saving that one up. Imaging is it’s own world – and very hard to put into words. To this day I’m still learning more about imaging and discovering new things – things which I originally thought were completely unrelated to the pan pot.

      Panning ties space, balance, rhythm, and width all together, so I feel it warrants it’s own article. It’s on the horizon, but I want to make sure I get it right.

  • Rhekluse

    I am looking forward to more articles!

    I also just emailed you via your website. Perhaps a friendly discussion on mixing could be had. 🙂

    Cheers, my brother.

  • SteveFroudist

    Thanks for the great articles!

    Speaking of panning, how about using two mono reverbs wide-panned to leave the centre +/- dry; using multiple reverbs to exploit the character of each, and playing back and re-recording your dry tracks in a real space .

  • All are great techniques Steve! The mono reverbs work really well went you want to create a wide image, like when you have spread guitar parts, or spread vocals in a chorus. Using a stereo reverb can pull the image inward a little, but using two mono reverbs that separation stays.

    Using multiple reverbs, or chaining delays to reverbs presents an unlimited number of possibilities. You can get really unique and crafted sounds this way. I use delays in conjunction with reverb fairly often, I don’t chain multiple reverbs too much so if you have techniques for this please share!

    Playing back and re-recording the tracks in an actual space is a technique that pre-dates digital. With a good set of speakers and a nice room and tracking setup you can get a real room response with much more accuracy to the source sound than convolution reverb based off an impulse response. Of course, actually tracking in room sound during the tracking phase is by far the most accurate (and fun, in my opinion).

    Thanks Steve!

    • SteveFroudist

      I often send a source to two or more reverbs to get a bit of the magic of each. I’ll sculpt the input of each with some high or low pass filters to adjust their color. But the best thing for me is, as you have pointed out, to get different sounds to feel connected. EG, I’m working on a track at the moment where I’m monitoring just the high hats, mandolin and banjo through a reverb, and getting the pre-delay just right so they all pulse together, rev time so the sound clears up in time, then add the dry sounds to adjust sends for front to back-ness. This may not be the main drum or instrument reverb, but it helps put them in the same room at the same time. I loosely group and monitor various parts of the mix to make “ensembles”, then when that sounds coherent, I combine and recombine. It’s interesting how this almost always results in being able to turn things DOWN when the spatial (and tonal) info supports rather than fights the music. When it works, it doesn’t need to be loud. I find I need very fresh ears to do this surgical work, but it pays off. A good mix can become great when it has subtle cues for our brains to work on. On the other hand, we can all recognise a try-hard, overworked mix.
      This for me is the key: as technicians, we need ears as measuring instruments, but as lovers of music, we should leave our analytical brains at home and listen with our imagination. Music is audible smell…it takes you to a place of feeling, not thinking.
      As for your last point, I was referring mostly to sampled sounds, DI tracks etc, where I don’t have access to any room sound.
      Sorry for the long rave!

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