Modular Synthesis (Part 9)
Using Sequencers with Modular Systems
More about modular sequencing and the effects it can be used for. Steve Howell educates.
Most synth players know all about what sequencers can do in conventional keyboard set-ups, but few are as aware of the possibilities a modular approach to sequencing can open up.
This month sees the continuation of the ongoing saga of how to go about sequencing with a modular synthesiser. Last month we looked at basic usage of simple digital and analogue sequencers for multi-voice, polyphonic sequencing, but the intention of this month's workshop is to explore more unusual applications, as it's here that the fun really starts. The possibilities for control are so much greater than on smaller instruments because of the access the user has to all the parameters on even the smallest of modular systems.
Those of you who are equipped with modest little analogue sequencers may well have run into problems trying to program rests or gaps into your sequences. This, of course, is a fairly straightforward procedure on digital sequencers where there's a button marked 'REST' or something similar for this very purpose and there are also some analogue sequencers that allow you to switch out steps in the sequence, but this facility is the exception rather than the rule and is usually reserved for the expensive models.
Rest programming gives you much greater sequencing flexibility, especially when multitracking or, as with last month's examples, when you are using more than one monophonic sequencer for polyphony. Figure 1 (a) shows a patch for rest programming with an analogue sequencer using the second CV channel to trigger the envelope generators. Whatever its make, your synthesiser will require a voltage to 'fire' the EGs, so it's best to program the CVs in Channel 2 so that some are above the required trigger level and some are below. Whenever the CV is greater than the required level there will be a note and vice versa.
Last month we saw that, despite their limited event storage, analogue sequencers score over their digital counterparts in that real-time interaction is possible with the sequence when it is running, and this is one example where this feature comes into play. By raising and lowering the CVs on Channel 2, you can drop notes in and out as you wish in an improvised manner, thus giving the impression of quite long sequences.
This is certainly preferable to the tedious eight-note sequences that trundle on aimlessly over the entire side of (too) many synthesiser music albums, and yet scores over the use of a microcomposer in that (a) you don't have to spend ages programming and (b) the results will be spontaneous as opposed to preprogrammed.
'But', I hear you cry, 'why can't I use the second CV channel to control the speed of the sequencer's voltage-controlled clock?' The answer is simple - because you won't be able to sync the sequencer to anything else such as another sequencer, a click-track, drum machine, or whatever. Using the method already described, you still have access to the sequencer's Step input so that synchronisation can be easily achieved.
One point to bear in mind, however, is that the EG's sustain level and decay/ release times must be kept to a minimum to give short, staccato sounds, otherwise you'll hear the VCO(s) move to the next step during the release cycle whenever there is a rest programmed for that next step. This can be useful, though, as it allows you to program tied and slurred notes into your sequence if you deliberately set the EG controls fairly high and, again, these tied notes can be introduced at will by tweaking Channel 2's CV levels when the sequence is running.
This technique can also be usefully employed to trigger another synthesiser voice, as shown in Figure 1(b). Here, the main sequence is provided by Channel 1, but Channel 2 is used to trigger the second synthesiser voice at preset gaps. Once again, by fiddling with Channel 2's CV levels you can make that voice sound whenever you like. Naturally, you'll have to tune Channel 2's synth so that it's in tune with the main sequence, and this can then be used to add a variety of on- and off-beat accents to the main sequence. Alternatively, you could use a non-pitched or noise source as the basis of your sound.
(Note: Those of you who are using Moog or Korg synthesisers will have to bear in mind that your equipment requires a trigger voltage different to that of most other synths. With Moogs, you'll have to set Channel 2's CV to give 12 volts for a rest, whilst 0 volts will trigger the EGs. Korgs, on the other hand, require a negative going pulse for a note to sound so Channel 2's CV has to be routed via an inverter.)
An extension of this technique (which has in fact been touched upon before in the article that looked at percussive sounds but which can be used just as effectively for pitched voices) is to use a sample and hold device to trigger the EGs randomly.
The patch is given in Figure 2(a) and you'll soon see that in this case the sample and hold is stepped through by the sequencer clock output. The random output is then routed to the EG trigger input so that whenever the random voltage rises above the trigger threshold level, the note will sound accordingly. Using this technique you can set up some fascinating effects in which notes suddenly appear at random, though their pitch has been pre-programmed into the sequencer.
One extension of this is to use the sample and hold to step the sequencer in a random manner (Figure 2(b)) so that, as well as the notes triggering at random, the sequenced notes also appear at random. This technique is more suited to accompanying a foundation sequence as a counterpart, and can sound particularly effective when the sequences are overdubbed and the sequencer and sample and hold are triggered by a click-track off tape. Alternatively, this patch could be used as part of a multi-voice sequencer set-up, with everything being triggered from a master clock from, say, a drum machine. Care must be taken to program notes into the randomly triggered sequence so that when notes eventually trigger, they don't clash with the main sequence. The total effect of this can be very interesting, as notes appear at random but dead on-beat. If this is multitracked a few times and then mixed down into a wide stereo image, notes will appear to 'bounce' from left to right.
Whilst on the subject of sample and hold devices, it might be a good idea to look at another technique that makes use of these (extremely useful) pieces of equipment. They have, in fact, been covered in past episodes so I won't dwell too long on them.
Referring to Figure 3, you can see that the CV output from the S/H is routed to the CV input of the VCF. You will also see that the S/H is being stepped by the sequencer (though this could be a master clock) so that for every step of the sequencer there is a random change in voltage from the S/H. This should enable you to create a variety of melodic and rhythmic sequences in which each note has a different tonal character. With high resonance settings on the VCF the tonal change will be quite drastic, but with low resonance settings the effect will be rather more subtle and, as well as tonal change taking place, there will also be an impression of level change, thereby creating random accents. This can transform an otherwise simple (boring?) sequencer pattern into something considerably more interesting and, using a fast tempo, you should be able to create powerful and dynamic rhythmic structures.
Feeding the white noise output of the noise generator into the audio input of the VCF should give the impression of the noise only sounding when the VCF is 'open' which will, of course, occur totally at random. In addition by routing the synthesiser into an echo unit whose echo speed is set to match the tempo of the sequencer the effect can be made more unusual still (especially when run in stereo), and by multitracking this technique, some incredibly complex polyrhythms can be set up.
There's no reason, of course, why the S/H shouldn't be routed to some other voltage-controlled device. My suggestions are the CV input of a synced VCO, the VCA, the PWM CV input of a VCO, or possibly the CV input of a voltage-controlled flanger or phase shifter, if you have these devices at your disposal. Whatever you choose to do with your Sample and Hold facility, beware. A lot of its possible uses have become terribly cliched in recent times, so take care to avoid these as far as possible.
All this by no means concludes the possible applications of sequencers in a modular system: next month we'll be looking at some other techniques which should give you an even greater sonic vocabulary to play with.
Feature by Steve Howell
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