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Guide To Electronic Music Techniques

Patchwork



With Spring hidden well around the corner, we think that reader participation is just what's needed to thaw out them old bones. So, PATCHWORK is for those amazing flights of synthetic fancy that you're just itching to spread across the oceans. And, so that you'll be persuaded to put patch to paper, we'll be offering regular prizes for the best patches printed on this page. We don't really mind in what format the patches are presented, i.e., you could use the sort of patch chart issued by manufacturers for their own synthesisers, or else you could work out all the "in machine" patch cords and draw out the patch using our suggestions for how you might go about doing this. If you felt super enthusiastic and wanted to make sure that we really appreciate your inventive genius, then a quick bit of dumping on to cassette of the final product, and the context in which you envisage it being used, wouldn't go amiss either. We feel it's wise to translate patches into a common language, rather than present a potentially confusing mass of different ways of doing virtually the same thing, so this is how your patches will eventually be printed. Finally, please make sure that you include all the relevant parameters critical to a particular patch. So, remember: PATCHES MAKE PRIZES!

Patch Principals



It's very easy to get confused between which "cord" represents what sort of signal in the majority of patch representations, so we think it makes good sense to distinguish between audio signals, control voltages (CVs) and gates right from the start, using solid lines for audio, dashed lines (---) for CVs and dotted lines (...) for gates and triggers.

That idea was taken (and slightly modified) from the excellent articles by Chris Jordan in the March and April 1981 issues of E&MM. PATCHWORK will always give credit where credit is due!

When it comes down to the actual shape of modules as they're drawn in patches, one can obviously do the logical and conventional thing of a square box with the initials of the particular device inside. On the other hand, there's also some sense in using shapes that signify more what the modules actually do. So, the remainder of this month's PATCHWORK will be devoted to presenting our ideas for shaping-up the common synthesiser modules.

VCO



A circle seems to be the best symbol for the VCO as it emphasises the cyclic nature of the output waveform. The CV enters from the left leading to an audio signal emerging from the right: We also need to include indication of such features as hard and soft sync (SYNC. H and SYNC. S, respectively), pulse-width modulation (PWM) and frequency modulation (FM) applied to either linear (Lin) or exponential (Exp) modulation inputs:

It seems sensible to apply SYNC to the top half of the VCO circle (imagine stamping on the CV—>audio line with your foot!) and modulation signals to the bottom half (the CV—>audio line balanced like a see saw on this input). It also helps to indicate the basic waveform type at the point of audio output from the VCO and at the point of any modulation input.

VCA



The ubiquitous op-amp gives the shape for this module, but, in this case, we suggest applying the CV from the top and any amplitude modulation (AM) from the bottom. This is admittedly twisting things around in comparison to the usual CV patching to a VCA, but it is in line with the logic behind the "vertical" inputs to the VCO circle. Let us know if you violently disagree! Some recent VCA designs (the Digisound '80 module, for instance) provide both exponential and linear control inputs, so the one actually used should be indicated with Exp or Lin at the relevant point. The waveform of the applied AM should also be shown.

ADSR



We've tried to be consistent in our approach to patches, and this includes the idea of using solid outlines for modules producing audio signals and dashed outlines for those delivering CVs. Envelope generators do the latter, of course. The introduction of the CEM 3310 voltage-controlled envelope shaper from Curtis Electromusic Specialities enables remarkable control to be exerted over all portions of the envelope, so we also need to include the potential of CVs being applied to the A, D, S or R control inputs — that's assuming you're lucky enough to have such a versatile beast!

Keyboard FM



We finish this month with a patch for FM, that much beloved tool of digital synthesists. The March '81 issue of E&MM explains the principles with crystal clarity, so I won't dwell on the theory. Suffice it to say that a modulating waveform (usually a sinewave) — from VCO1 in our patch — is applied to a carrier waveform (also a sinewave generally) — from VCO2 — producing an output with added harmonic components above and below the original carrier harmonics — hence the logic of using a carrier with only one harmonic component, i.e., a sinewave. The patch makes use of the effect of a change in the modulating index (the ratio of the FM-induced frequency deviation to the modulation frequency) produced by applying a keyboard-triggered envelope to the modulation signal from VCO1 fed to the linear FM input of the carrier oscillator, VCO2. This results in a more or less subtle change in the emerging harmonic spectra, the so-called dynamic depth FM synthesis. This is only a basic FM patch, but it should give some idea of the potential of the technique in analogue synthesis. What about some variations on this theme? The shape for the keyboard in this patch continues our policy of dashed lines for nonaudio-producing modules, and, with just a single gate and CV output, there's nothing more to say about it!

FM patch.


Finally, some acknowledgements (other than those mentioned) for this month's PATCHWORK and future pages: PAiA's "The Source" (not to be confused with Moog's new machine!) — an interesting, if somewhat quirky view of patching, and totally geared towards their own modules; "Electronic Music Synthesisers", by Delton Horn — a useful source of info on a variety of synthesisers (though a few years out of date — no Prophet 5!) and includes some cheap, cheerful (if rather inaccurate) circuits for voltage-controlled and non voltage-controlled modules; "Musical Applications of Microprocessors", by Hal Chamberlin — definitely worth acquiring by hook or by crook, and full of invaluable stuff on analogue circuits as well.



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Batrachophrenoboococosmachia

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Sequential Circuits Pro-One


Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.

 

Electronics & Music Maker - Mar 1982

Feature by David Ellis

Previous article in this issue:

> Batrachophrenoboococosmachia...

Next article in this issue:

> Sequential Circuits Pro-One


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