Making sounds with analogue electronics - Part 7: Topology of a typical synthesizer

Performance synthesizers (monophonic or polyphonic) need a simplified and ordered control panel in order to make them usable in live performance. For this reason they usually have a fixed topology of modules: VCO, VCF and VCA.

Analogue modular synthesizers are not arranged in a logical order because there is no way to anticipate what they will be used for, except for the simplest cases. The most usual arrangement has the oscillators and other sound sources grouped together, usually on the top or on the left, with the modifiers (filters and amplifiers) in the center or middle and the EGs on the right or bottom.

Performance instruments have memories that can be used to store and recall sounds or timbres quickly. They are often used as replay machines for a series of presets.

Modular synthesizers normally have no memory facilities, or very simple generic ones which do not have the immediacy of those found in polyphonic instruments (Figure 3.6.5).

FIGURE 3.6.5 (i) A performance-oriented synthesizer is designed to rapidly recall stored sounds and allow detailed performance effects to be applied with a range of specialized controllers. (ii) A modular synthesizer provides a wide range of modules which provide great flexibility, but at the expense of complexity and ease-of-use.

Performance synthesizers have modules arranged in a way that enables quick results: VCO–VCF–VCA with EGs. Modular synthesizers have few preset connections, if any, and so whilst it is quick and easy to connect a VCO to an amplifier and get a sound which will play until you turn the VCO or amplifier off, it can take some time to get a sound from a modular synthesizer which can be used in conventional performance.

It has been said that modular synthesizers are the ultimate synthesizers and that it is only time that limits people's use of them. Actually, modular synthesizers are severely limited by a combination of the design and the user. The design is limited by the problems of trying to cope with patch-leads and lots of controls underneath.

The user is fully occupied trying to hold everything about what is happening in their head: a simple VCO–VCF–VCA setup with a couple of EGs can be spread over more than a dozen modules and 20 or more patch-leads. The limitations are all too evident: no programmability, a confusing and obscure user interface and lots of scribbled sheets noting down settings and patches. They are also often write-only devices – once the user has produced a patch, coming back 3 months later and trying to figure out what is happening is almost impossible. It is often much faster to start all over again.

Modular synthesizers are very good for appearance. Large panels covered with knobs, switches and patch-cords can look very impressive on stage. In reality, modular synthesizers are very good at producing lots of variations on a very specific set of sounds, and not very much outside of that set. Some

FM-type sounds can be produced, but not very usefully, since the VCO modulation at audio frequencies is often less than ideal. Filter sweeps have a nasty habit of getting bored too, and it is very easy to fall into the 'lots of synth brass sounds' cliché. And do not forget that beyond about 20 patch-cords, most people lose track of what is connected to what!

Modular synthesizers can be considered as almost 'write-only' devices, where trying to work out what a patch does can be very difficult, especially if someone else did the patching. It is also often forgotten that despite the large number of modules which are available in many modular synthesizers, their polyphony is very limited: two or three notes and frequently only one note!

Modular synthesizers are really not designed for polyphonic use, and trying to keep several separate sets of modules with anything like the same parameter settings is almost impossible. Although sampling the sounds that are produced using a modular synthesizer can be one way of producing a polyphonic sound and having programmability, given the synthesis power of many hardware and software samplers, the modular synthesizer is almost redundant even for this application.

Perhaps the most persuasive argument for the limited timbre palette of modular synthesizers is stored forever in recordings of the early 1970s. The problems of keeping track of patch-cords, the very limited polyphony, trying to avoid sweeping filter clichés, attempting to stay in control of the sound, the complete lack of any memory facilities and other limitations all conspire to make modular synthesizers an expensive chore.

Of course, from a very different viewpoint, modular synthesizers are collectable and may well be sought very well after in the future as 'technological antiques'.

3.6.5 Keyboards versus other controllers
Most synthesizers come with a keyboard. Most expander modules are equipped with MIDI input, which is a strongly keyboard-oriented interface. Many of the controls on a typical synthesizer are monophonic keyboard-oriented: pitchbend, modulation, keyboard tracking, after-touch, key scaling,…

Alternative controllers often have different parameters available which are not keyboard related. Stringed instruments such as violin and cello have control over the pressure of the bow on the string in a way which is analogous to velocity and after-touch combined.

Guitars enable the performer to use vibrato on specific notes: something which is very difficult on most keyboard-based synthesizers. Woodwind instruments have a number of performance techniques that do not have a keyboard equivalent – like pitch-bending, changing the timbre or producing harmonics, all by using extra breath pressure and lip techniques. (Additional information on controllers can be found in Chapter 7.)

Coming up in Part 8: Topology - Early versus modern implementations.

Printed with permission from Focal Press, a division of Elsevier. Copyright 2009. "Sound Synthesis and Sampling" by Martin Russ. For more information about this title and other similar books, please visit www.elsevierdirect.com.

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