Continuing on from where we left off in March, this PATCHWORK finishes the less than edifying business of shaping-up synthesiser modules, but fear not, gentle reader, great things are around the corner!

VCF

The variety of ways in which VCFs are configured warrants some attempt to give them distinguishing shapes in patch diagrams, and so, for high-pass, band-pass and low-pass filters, we've gone for the following:

There's nothing much that's controversial here, and it seems perfectly reasonable to use the filter's approximate response curve for its shape. The only problem with this is when you have awkward things like notched filters — shark's teeth here we come!

Noise

We thought of using a broken line for the circle (noise isn't exactly cyclic, is it?) and colouring-in with pink or red when the noise wasn't white, but, in the end, our noise generator is just a plain and simple circle with R, P or W at the output to indicate the complexion of this universal panacea for all synthetic ills.

Sample and Hold

Some synthesists treat the combination of Noise and Sample and Hold like their bread and butter; others can tell marge from the real thing and exercise a bit more caution in extolling the virtues of such auto-synthetic techniques. Still, the old S&H is invaluable for deriving CVs from audio inputs and deserves to be considered with a little more care than the average prepackaged, pre-processed pat of non-dairy origin.

Ring Modulator

Without ringing the necks of a few waveforms, the Daleks would never have arrived on the scene and, though these cuddly creatures' voices could hardly be described as being particularly melodious, today's ring modulators make much better musical sense and are invaluable for synthesis of those inharmonic timbres typical of bells, gongs and the like.

Note the C for 'carrier' and M for 'modulator'.

Mixer

With multi-modular systems, some mixing prior to the final output is necessary to put everything into some sort of perspective. For many synthesisers, mixing is something of an afterthought and rarely goes beyond the passive variety. In the case of the mixers in the Spectrum synthesiser and the Digisound '80 range, this humble unit is transformed into an important sound-shaping module, and, in the case of the latter's voltage-controlled mixer, includes voltage control of each of the four inputs as well as control of stereo panning. Taking a 4 into 2 mixer as our example, a typical voltage-controlled mixer might be represented as follows:

LFO

The difference between LFOs and VCOs is only really a question of the degree of oscillation, and so the VCO circle is employed for this module as well.

Manual control of LFO speed is obviously more often the rule than voltage control, and the same point applies to the option of PWM or FM, but there are some LFO modules which allow for this (the Digisound LFO, for instance). Esoteric stuff!

That completes our round-up of basic synthesiser modules; next month we'll progress into patch building proper. To ring out this PATCHWORK, I've included a BELL patch on which to practice your campanology.

The tuning of the VCOs is particularly important to realistic simulation of bells and the suggested major 6th and minor 2nd offsets are one way of getting a good sound. The ring modulator helps to beef up the sound, and the contrary motion of VCF2 and 3 duplicates the curious harmonic envelopes of large cathedral bells. The top section of the patch, i.e., that around VCO1, VCF1 and VCA1, is a clapper simulator and it's obviously important to choose a reasonable pitch setting for VCO1. A further ADSR could be added in to control mixer panning, but maybe that's just gilding the lily!