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Creating Rhythmic Gate Effects

Tips & Tricks By Paul White
Published September 1996

Paul White reveals how to create rhythmic gate effects, both using conventional hardware and MIDI Controller information.

Gates were originally intended as utility devices for the removal of noise during pauses in programme material, and their use in this capacity is probably well understood by the majority of SOS readers. At its simplest, a gate is just an electronic switch which mutes the signal when it falls below a certain level.

Since gate manufacturers started fitting their products with external key or side‑chain inputs, the gate has had its status elevated to that of 'special effects unit', and the purpose of this brief article is to look more closely at the creation of gate effects. If you read the manufacturer's user manuals, they'll nearly always cite the example of using a gate to 'tighten up' a sloppy bass part by gating it from the bass drum track, thus helping synchronise the two sounds. Although this is a very rudimentary use of the side‑chain input, it does serve to illustrate how the setup works. More contemporary gating effects include chopping up a sustained sound (such as a synth pad) to generate a rhythmic sequence or even using both channels of a dual gate to create a stereo effect where the rhythms dance from left to right.

Chop 'Em Up

In some ways, an externally triggered gate bears a close resemblance to a computer logic 'AND' gate, since you get no output unless both inputs are present. You need an external key signal to open the gate, and there has to be a signal present at the main audio input of course before you hear any output. Only when the two signals coincide will an output signal become audible. Figure 1 shows how this type of side‑chain triggering works; a continuous signal at the main input is chopped into bursts by a rhythmic input at the Key In socket. This rhythmic input can be derived from anything — from a staccato synth pulse to the hi‑hat or kick drum output from your drum machine. In fact, any sound with a clearly‑defined start and end will do the job.

The cleanly chopped output is dependent on the gate being set to a very fast attack time and a very fast release time. If you inadvertently set a long release instead, the gate will barely have started to close when the next pulse comes along and opens it again, so you won't achieve the desired chopping effect. However, if the gate opens so fast that it causes an unpleasant click, you should slow the attack down slightly by increasing the attack time setting, to smooth it out a little.

Hold On

When creating gate effects, the gate's Hold control is vitally important because it allows you to set the duration of the triggered bursts with rather more flexibility. If your gate doesn't have a Hold facility, then the output bursts will always be the same duration as the Key input sounds, and if the Key signals are drum beats, the resulting bursts might be too short. By using the Hold control, the burst length can be extended to an artistically correct amount.

A number of dance‑style records make use of rhythmic gating to drive the music along, and because of the precise nature of the gating effect, the result is as musically tight as the rhythm doing the triggering. It's most common to use the effect in conjunction with a sequencer, because you can dedicate a separate track to controlling whatever sound you are using as a trigger. You can also quantise, where desirable, to ensure a high degree of rhythmic precision. A great many multitimbral synth modules have their own built‑in drum parts and it's unlikely that you'll need them all in your composition, so one drum sound can be reserved as your gate trigger source. For example, in my own setup I use an Alesis D5 as my main drum sound source, but drum sounds are also available from my Sound Canvas, Roland Vintage module, my Emu Proteus and Morpheus. In this instance, however, you do have to ensure that your trigger source signal is not mixed in with any other sounds you may want to use in the mix, which means either using a module with assignable outputs (such as the Proteus), or dedicating a whole synth module to the job of gate triggering. So, if you have an old module (single or multitimbral) that you don't use much, it may be worthwhile keeping it purely for triggering purposes. A sound module with a stereo output and pannable sounds is also beneficial for the creation of stereo effects, as I'll explain later.

If you don't have a drum sound source which you can use for triggering, then any short synth sound with a fast attack and release will do the trick. At a push, if your sequencer is synchronised to your multitrack recorder, you can easily record your trigger source onto one track of tape, thus freeing up your sound module if you need to use it elsewhere in the mix.

What Works?

Sustained sounds work best because, when you chop them up with the gate, the rhythmic pulses will be reasonably consistent in level. Guitar is a good candidate, but it needs to be either compressed or overdriven to get the required density of sustain. I find that a mild overdrive combined with loads of compression usually works well.

Other useful sources of 'chop fodder' include layered backing vocals, E‑bow guitar (a simple electronic sustaining device), rainsticks (or any other form of percussion that can be shaken or rattled continuously), or sustained keyboard chordal pads. You can even take parts from another song (ideally in the same musical key), and chop them up to provide a rhythm.

To create the stereo effect mentioned earlier, you simply record two different rhythms into two tracks of your sequencer and then use these to trigger different sounds panned left and right in your trigger source synth module. These two rhythmic signals are used to trigger the two channels of a dual gate and the same 'chop fodder' signal is fed to both gates. All you have to do is pan the gate output signals hard left and right in your mix and the two rhythms will cause the finished sound to dance from left to right speaker. Figure 2 shows how to create a stereo chopping effect.

Gateless Gating

Those of you working entirely with sequencer controlled MIDI sound sources can recreate most gate‑style chopping effects entirely via MIDI. Ideal sound sources might be a pad from a synth or a looped guitar chord from a sampler, and the only requirement is that the instrument responds to Controller 7, so that you can adjust the volume using MIDI data. Now all you have to do is tap in your guide rhythm pattern (or use an existing rhythm track), then go into edit mode and insert a Controller 7, value 127 event whenever you want the sound to switch on and a Controller 7, value 0 event wherever you want it to switch off. To save yourself time, you only need to construct one bar of this, then you can simply copy it within your sequence track. In fact, if you use one of the better sequencer programs, you'll invariably find a means to input this Controller data graphically, which makes life even easier.

Although this is a very easy way to create gate effects, you can buy pre‑programmed MIDI files containing Controller data that provide ready‑made gating effects for you to paste into your own music. I use the Twiddly Bits Bytes and Pieces collection, which is regularly advertised in the SOS classifieds, but Heavenly Music and Hands‑On offer similar products. If you have the patience, you can build up complex rhythms encompassing a number of sequencer tracks and a variety of different sound sources, and because MIDI sounds are easily panned, you can also generate some exciting stereo effects. Processing such rhythms via tempo‑related delay effects can also help you weave an even more complex rhythmic web. Experimentation is the name of the game here.

No Limits?

Gating effects are normally discussed in the context of dance music, and there's no doubt they are immensely useful in this field, but the same effects may also be applied to pop music, soundtrack work and even ethnic music. For example, you could take a digeridoo loop and chop that up into a rhythm with an ethnic feel (some less‑than‑kind readers have simply suggested chopping up my digeridoo to cut out the middle man!). You can do the same thing with sitar drones, hurdy gurdy or tambura, while nearer home, you can find unlikely sources of inspiration in gated vacuum cleaners, washing machines, power tools or industrial factory noises. For new age music, you can chop up recordings of mountain streams (which is far more environmentally friendly than chopping up rainforests!), or you might like to turn your attention to the elements and try chopping wind, rain or the stormy sea.

In the final analysis, rhythmic gating is a very simple effect to achieve, but don't write it off as being trivial just because it is simple. Take the time to experiment and you're almost certain to come up with something that takes both your creativity and your music in new directions — and that's what most of us really need.