Having concentrated on pitched sounds recently, Steve Howell takes an in-depth look at the generation of percussive voices which can either be played manually from your synthesiser's keyboard or triggered from a drum machine's clock or trigger outputs.

This month's feature looks at conventional drum-kit sounds and how to synthesise them: more exotic 'electronic' voices will be discussed next month. Some sounds are - not surprisingly - easier to simulate using a synthesiser than others, as you'll see under each individual sub-heading.

Snare Drum

The snare is basically an ordinary two-headed drum which has underneath it a set of wires (the snare) which vibrate in sympathy whenever the drum is struck, and it is these snares that give the drum its' characteristic 'crack' - take the snares off and it sounds like an ordinary drum. These two elements can easily be synthesised on even the most basic synth but a modular instrument will give you far more control over the final sound than any pre-patched instrument or drum synth module.

Referring to Figure 1, you will see that we have two 'channels' - one for the pitched drum and one for the snare (the noise generator). You will note that there are no filters involved: this is a matter of taste as you can filter the noise generator for special effects if you wish, though for a realistic snare sound I prefer to leave it out. Choose a sinewave from the VCO or failing that, a triangle wave, though I feel a sine is usually more effective. If your VCOs don't have a sinewave output (and many don't), use a VCF with the resonance control full up as this can produce a very pure and undistorted sine that is particularly good for drum sounds; indeed I find myself using this method even though my synth does have VCOs with sinewave outputs.

By careful experimentation with the tuning of the VCO and with various ADSR times, you should be able to create a host of snare drum sounds from a deep concert snare to the high, Bill Bruford snare sound as well as many synthesiser snare effects and 'cracks', the VCO adding more depth than if you used the noise generator alone. As with a real snare drum, the sound can be improved with judicious use of EQ on the mixer or by adding reverb, and there's no reason why you couldn't process the sound through an outboard effects device for further variation. A harmoniser will provide you with a reasonable approximation of the deep share sound Bowie used on the album Low, for instance.

Bass Drum

The bass drum is in actual fact quite difficult to synthesise, but it is a very important part of modern music, so it's worth spending some time getting it right. Figure 2 shows a patch for a bass drum sound. Again, there are two channels, one which handles the 'click' and the other the drum itself. Although there are no vibrating snares on a bass drum, the noise generator can still be employed to add the percussive 'click' that is very much in vogue these days - it's not essential but it does help the bass drum to cut through the mix when lots of other instruments are added. Again, as with the snare drum, the pitched element can be derived from an oscillating VCF. The ADSR times must be extremely fast and the best results will probably be obtained by tuning the VCO (or VCF) right down to minimum and adjusting the EG sweep to create the sound you require. Unfortunately, Daniel Miller, whose bass drum sound is just about the best I've ever heard, is not prepared to divulge the secret of how he obtains it, but suffice to say it is produced in much the same way as the method outlined above, using an ARP 2600.

As with any acoustic bass drum, you can employ all sorts of tricks such as compression and copious amounts of EQ (usually, hefty top boost to emphasise the 'click' and low cut to attenuate the 'boom') to tailor the synth sound to your needs, and you can then trigger it off your drum machine (if you have one) to augment or replace the unit's bass drum sound.

Toms

The patch in Figure 2 can also be used for these drums, but this time with longer decay and release times on the EG to allow for the natural 'ring' of toms. You can adjust the sweep of the EG to suit the sort of effect you are after, and adjustment of each of the channels will enable you to create an assortment of tom sounds from realistic synthesis of acoustic toms through thundering Simmons to cheap and nasty 'pew-pew' effects. Reverb will enhance the sound as will EQ. You might also like to use this patch for a snare drum as it is currently very popular to have a degree of pitch sweep on the snare sound.

If you think the patches look similar to a Simmons module or E&MM's own Syntom modules, you're right, except that in these examples, the noise element (which is actually a very important sound of a drum) has its' own envelope shaper. One of my major criticisms of all the drum modules currently available (manufacturers please take note!) is that the noise and the pitch elements both share the same envelope generators, which results in long 'splashes' of noise in the context of long decay times.

This can be very effective but there are many occasions when it isn't, in which case I ditch the Simmons in favour of my trusty modular ARP. Using the patches I have given here should enable you to obtain long pitched decays with just a short burst of noise for the attack transient, and this is often much more effective. It also means that you can individually EQ and process each separate element of the sound for even further control. What you lose, however, is the drum 'feel' and the touch-sensitive properties of pads, but for the bass and snare sounds this needn't be as much of a problem as it sounds, as a lot of modern music relies heavily on an unfaltering, solid back-beat. You also lose the acoustic 'spacing' of having separate tom modules panned across the stereo image, but this can be partly overcome by panning the mono sound manually during mixdown or by creating a pseudostereo effect with double-track echo, chorus or mild flanging, or by using a stereo reverb. On the whole, though, these patches will give you a lot more creative possibilities than most commercially available units, and they can also be usefully employed giving the sounds of your drum machine more variation.

Additional Percussion

The rest of the kit is not so easily synthesised, however. Cymbals are notoriously difficult to recreate which is why some drum computers use sampling even when all the other drum voices are synthesised. To be perfectly honest, to date I have not been able to capture the sound of any 'kit' cymbal on a synth, but it is possible to create a sound which can be effectively used in place of a cymbal using a ring-modulator.

Referring to Figure 3, you can see that two VCOs (using the sinewave outputs again) are fed into the RM, and that by tuning the VCOs to various intervals you can create some interesting metallic sounds: the sum and difference frequencies produce the dissonance cymbals are famous for. You will note also that a noise generator has been used to create the 'splash' of the cymbal and if you wish, the noise generator can be used on its' own as an effective cymbal substitute. I recommend you put the metallic element of the sound through slow, mild flanging, as this may help a little, as will a slow, mild sweep of one of the VCOs by an LFO. More VCOs might help you build up a more complex cymbal sound. Alternatively, you could adopt Peter Gabriel's 'no cymbals' philosophy...

Hi-hats, particularly the closed variety, are not so difficult and Figure 4 shows a simple patch which should supply you with an effective, metallic 'tick'. The resonance of the VCF is set to a point where it is on the verge of oscillation and the cutoff frequency should also be set fairly high, depending on the effect you require. By triggering this on 8th or 16th notes you should be able to provide an effective hi-hat pattern, or alternatively, make use of the programmable trigger output from a drum machine to set up a more intricate rhythmic pattern. One interesting effect you can use is to program the drum machine's hi-hat and the 'external' hi-hat on alternate beats panning the sounds hard left and hard right respectively to give you a 'ping-ponging' effect.

Unfortunately, open hi-hats are not so easy and require a separate trigger pulse and voice module. Use the patch in Figure 4 but adjust the ADSR times to give a slower decay and release with full sustain. By leaving a gap in the closed hi-hat pattern and triggering the open hi-hat in the gap, you should be able to create the effect of an open and closing hi-hat rhythm: however, you will probably need to gate the open hi-hat to sustain it a little and the decay/release times will have to be adjusted very delicately to close on the arrival of the next closed hi-hat. Be prepared to spend a lot of time on this one as it is quite a tricky procedure. As with the closed hi-hat, the cutoff frequency can be adjusted to taste, though it's as well to keep it the same as that of the closed hi-hat, thus ensuring some consistency between the two sounds.

To obtain these sounds simultaneously without resorting to overdubs (which can use up a lot of tracks on the tape machine) you'll not only need to have a lot of modular hardware but also a very sophisticated drum machine with a lot of trigger outputs, or else a multi-channel trigger sequencer. I doubt if many amongst you have such facilities, but simply using one or two of the patches given should greatly improve your drum sound.

Summing-Up

In fairness, even the humblest of drum machines can provide quite good and useable drum sounds these days, and it would appear that there are more to come. As technology brings the price of equipment down, the need to go to elaborate lengths to create these sounds will diminish, but it's worth bearing in mind that as these devices become more readily available (and at more reasonable prices) there's a growing tendency for machines to sound 'samey', and this is especially true of drum sounds (have you played 'Spot-The-Linn' at a disco lately?), so even if you do opt for the new breed of drum synthesising devices, it's worth considering setting up some of these patches as an alternative. They can sound equally as effective as any commercially available 'off-the-shelf' device, though possessing at the same time a distinctive character of their own.