This month, Paul White turns his attention to reverb treatments for music production, with a closer look at what works with drums and percussion.

Last month I covered some of the psychoacoustic principles of reverb and looked at some ways of applying them to vocals. Because artificial reverberation is based on a natural acoustic phenomenon, it is a very powerful creative tool in music production — the audio equivalent of lighting in photography, if you like. Without light and shadow, photographs would appear very flat and two-dimensional, and the same is true of recorded music.

In the western world, we are used to hearing our music played indoors, and all buildings have acoustic properties of one kind or another. Natural concert hall reverberation could be considered as the equivalent of natural lighting — everything is illuminated by the same light source, all the shadows fall in the same direction and everything feels very comfortable and homogenous. Pop music production, on the other hand, tends to make use of a variety of different reverb treatments within the same mix — the vocals may have a long reverb, the bass may have little or no reverb and the snare drum might use gated reverb. This can be considered equivalent to a carefully-lit film set, where different lights are used to create specific effects of light and shadow rather than emulate nature. And, just as set lighting can make or break the look of a film, the use of reverb in a mix can either turn a good recording into a masterpiece or reduce it to a swirling mess of sound.

You may recall that last month I stressed the importance of leaving space within a mix. You may need to keep reminding yourself of this, because when you spend good money on a digital reverb unit, a very natural instinct is to ensure that everybody hears it! Very often, when the inexperienced enthusiast goes into the music shop looking for a suitable reverb unit, one of his or her first questions relates to how long the reverb time can be made to go on. This may be a consideration when creating special effects, but a more important question is how short the reverb will go without becoming hard or clangy — particularly important because the majority of reverb treatments are short; much of the time you wouldn't even know that a short reverb treatment was being used unless someone suddenly switched it off mid mix.

Before diving in to look at specific treatments for different instruments, there are a few very general rules — though you should feel free to break every single one of them if you feel you have a good artistic reason for doing so!

- Firstly, if you want to use long reverb sounds to create a special effect, make sure that the arrangement leaves space for the reverb to be appreciated. In practice, this means avoiding having too many midrange sounds layered over the top of the reverb. As a rule, a few bright, tinkly sounds at the top end of the spectrum won't get in the way of your reverb and, by the same token, a bright reverb will still be audible over a low bass note. If you want to use reverb to create the illusion of spaciousness, what you should avoid are very dense electric guitar or keyboard pad parts. These observations are even true for New Age musical styles, where long reverbs appear to be the norm. You'll find that in well-arranged pieces, the longer reverbs are not fighting with other sounds, while other instruments may be treated with much shorter settings. The analogy with lighting holds up here too — a single lamp-post in the centre of a side-lit stage will cast a long and dramatic shadow; if the stage was full of closely-spaced objects, the shadow would be broken up and would serve to confuse rather than enhance.

- Secondly, the musical part being treated shouldn't be too busy if long reverbs are to be allowed to work. The only way you'll effectively combine busy musical lines and long reverb times is if you employ the reverb ducking technique described last month. This will keep the level of the reverb down during periods of intense musical activity and then allow it to swell in level at the ends of phrases. It's well worth experimenting with this technique, as it genuinely helps keep a mix clean sounding.

- Thirdly, the majority of the energy in a pop mix is at the bass end, so avoid adding much in the way of reverb to bass sounds such as kick drums, bass guitars or bassy synth lines. If you find that a significant degree of reverb is needed on one of these sounds for artistic reasons, then it helps to EQ the reverb return to roll off the bass end. Even a simple two-band EQ is OK for this — just turn the Low control well down.

- Finally, try to get your mix sounding well-balanced and complete before you start to add reverb. That way you'll find you need to add less, which inevitably results in a cleaner, punchier mix. Keep in mind that our brains interpret large amounts of reverb as distance and that nearby, intimate sounds invariably have a lower level of reverb; when we listen to something that's very close, the majority of what we hear is the direct sound.

Having dispensed with the generalities, it's time to move on to specific instruments, the first being the all-important drum kit.

Drums And Percussion

Most recording projects involving drums still make use of close miking, though there is a growing awareness of the importance of ambient mics placed further from the kit. In smaller studios, close miking offers good separation between the individual drums and, to a great extent, removes the drums from the effect of their acoustic surroundings. As a result, a mix taken directly from the close mics will sound pretty dry.

KICK DRUMS are usually left fairly dry (remember my previous remarks concerning reverb and bass sounds?) or treated with a short, snappy reverb treatment such as a small room, early reflections only or plate setting.

SNARE DRUMS tend to benefit from more added reverb, and a plate setting is the traditional choice, partly because it mimics the rock drum sounds of the 70s, which were created using real plates. Plates also have a fast attack and a bright tonality which helps reinforce the attack and definition of the snare drum. Longer plate settings can be used to create a very transparent, steamy kind of sound, but here it can help to roll off some of the bass to prevent things getting out of hand. As a very general rule, the longer settings work best on slower pieces of music or songs with sparse instrumentation.

A typical snare reverb might range from as short as half a second for a tight, bright sound to over two seconds if an obvious effect is required. When using very short reverb settings, it is usually possible to use a higher level of reverb without swamping the sound; a useful trick is to pick a very short, very bright setting to add snap to a dull snare drum. For a bigger sound, pick a short hall setting, which should be warmer and have a slower build-up or attack.

TOMS, contrary to popular belief, don't need masses of reverb, as they tend to have a natural sustain to their sound anyway. Plate or small room settings work well in pop music, with longer settings being appropriate for heavy metal or down-tempo progressive rock. For an illustration of the latter, check out the Pink Floyd albums made over the past decade or so. You'll also hear some fairly long drum reverbs on the introduction to Dire Straits' 'Money for Nothing', but take note of how much space they've left to allow the reverb to work. As with the snare drum, hall settings can be used as an alternative to plate emulations to give a very 'big' sound.

HI-HATS benefit from a short-to-medium bright setting, and one with a high level of early reflections can add interest and detail to the sound. Indeed, it's worth trying out reverb patches with high levels of early reflections, or ambience patches that are all early reflections with no reverb, on all the drums, just to get a feel for what can be achieved. In most cases, you'll notice a dramatic increase in the sense of 'being somewhere real' but without spreading the sound out too much. This type of setting is ideal for music that needs an intimate, club-type atmosphere. Add some pre-delay — between 50 and 100mS — and the sound takes on a kind of 'slap-back' feel which also works well under some circumstances. However, if the pre-delay is too long, it can affect the apparent rhythm of a piece.

Being able to pick different kinds of reverb for every drum and cymbal is all very well in a top professional studio, but for those of us working at home, one reverb unit often has to be used for everything. Similarly, if the drum sounds come from a drum machine or sampler, it may be impossible or impractical to separate the different sounds. For example, a drum machine with only a simple stereo output forces you to compromise between separating the kick drum from the rest of the kit (by panning the kick to one side and the rest of the kit to the other) or keeping the stereo image created by panning the individual sounds to their correct positions. If you have a MIDI-to-tape sync system, you could record the separate drum sounds onto their own tape tracks in separate passes, by muting the unwanted sounds on each pass, but this is time consuming and rather less than fun.

If you don't want to go to all this trouble or don't have many tape tracks to play with, simply feed the whole drum kit through the reverb unit with a short plate or early reflections setting and turn down the bass on the reverb returns so that the kick drum doesn't cause too much of a mess. Used with restraint, this simple measure can actually be very effective and comes quite close to to the sound you'd get miking a kit in a naturally live room. This type of natural sound is currently very popular, so being forced to use it isn't too much of a compromise!

Percussion sounds also benefit from the sense of space and depth reverb can provide, though very little reverb is necessary for creating the illusion of spatial identity. Even so, ethnic and Latin percussion is an integral part of New Age and experimental music where long reverb settings can used to fill space in an interesting way. As ever, the musical arrangement must provide the space in the first place, but it is not unusual to hear delicate instruments such as triangles or shakers treated with cavernous hall programs. Because many of the instruments occupy the mid and upper register of the audio spectrum, you can afford to be quite adventurous with the reverb treatments without worrying too much about muddling the bass end of the mix.

Gated Reverb

Gated reverb is a familiar feature of virtually every digital reverb unit, but it stems from a technique devised using nothing more than a reverberant room, a couple of mics and a couple of gates. In essence, the mics were set up well away from the drum kit so that they picked up mainly reflected sound and then the results fed to a gate which was triggered, via its external input, from the close mics on the drum kit. Often the natural reverb was also compressed to increase the sustain time, and, if you look at Figure 1, you can see exactly how this is arranged.

To create the popular gated drum sound, it is important to use a gate that has a variable Hold time as well as an attack and release control, the Drawmer DS201 being the first gate to incorporate this feature; it should be set with a fast attack, a hold time of around half a second and the fastest release time possible. Whenever a drum is hit, the gate is opened for the half-second period set by the Hold control and then it snaps shut, muting the reverb very abruptly. Most people associate this effect with the classic Phil Collins drum sound.

Modern reverb units fake this effect by creating a burst of reverb comprising several early reflections which finish abruptly, as shown in Figure 2. As a rule, there is no gate threshold to worry about so the effect can be used 'straight out of the packet', but purists still insist that the original method sounds best. Interestingly, gated reverb can also work very well on sounds such as raunchy guitar and sometimes even vocals. What is really effective about gated reverb is that you can use lots of it, even on kick drums, and you still don't lose the spaces in your music.

The way in which we perceive loudness in a mix is, in part, related to the contrast between the loudest sounds and quietest sounds, so by using a gated reverb and keeping plenty of space, you can create a sense of power and energy without any increase in actual volume. The downside is that gated reverb is such a well known and obvious effect that you have to use it sparingly if you don't want your mix to sound dated.

Next month, I'll be looking at ways of using reverb with other instruments, and describing some interesting reverb production tricks.