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

Monophonic synthesizers tend to be performance-oriented instruments designed for playing melodies, solos or lead lines. Despite the name, many monophonic analogue instruments can actually play more than one note at once: many have a duophonic note memory that allows two different note pitches to be assigned to two VCOs. With only one or two notes capable of being played simultaneously, an assignment strategy is required so that any additional notes played can be dealt with in a predictable way.

Two common schemes are last-note and low-note priorities. Last-note priority is a time-based scheme, which always assigns the most recently played note to the synthesizer's voice circuitry, whilst low-note priority is a pitch-based scheme, which always assigns the lowest pitched note to the voice circuitry.

Low-note priority can be a powerful performance feature; for example, the performer can play legato 'drone' notes with the thumb of their right hand and use the rest of the fingers to play runs on top, with staccato playing dropping back to the 'drone' note. This technique is most effective with envelopes that are not retriggerable; that is, they do not restart the attack segment each time a new key is pressed on the keyboard. See Chapter 7 for more details on keyboard design and note assignment.

Portamento is a gliding effect which happens between notes. On a monophonic synthesizer it is normally used as a performance effect to give a contrast between the sudden pitch transition between notes and the slow change of a portamento. The portamento circuits in analogue synthesizers work by restricting the rate at which a CV can change. Normally, the pitch CV from a keyboard will change rapidly when a new note is selected. A portamento circuit changes the slope of the transition between the two voltages. It thus takes time for the note to move from the existing pitch to the new pitch (Figure 3.6.2).

FIGURE 3.6.2 Portamento provides a smooth transition between successive pitches from the VCOs. The time taken for the keyboard CV to change from the previous value to the new value is called the portamento time.

Glissando is a rapid movement from one note to another where the pitch changes chromatically through all the notes in between. At fast speeds, glissandos sound similar to portamento.

Monophonic synthesizers normally arrange the front panel controls so that they form a logical arrangement, often mimicking the topology of the modules inside. The front panel is normally arranged so that sources and controllers are on the left, with modifiers and the final output on the right.

Early analogue monophonic synthesizers, and most modular systems, do not have any form of memory for the positions and settings of the front panel controls, and so a clear and functional arrangement of controls can aid the user in remembering settings. The process of using such a synthesizer requires a lot of practice to become thoroughly familiar with the workings of the instrument.

Recalling a sound is often achieved iteratively, with adjustments of the controls gradually homing in on the required sound. Individuals who have mastered a synthesizer in this way have many similarities to a classically trained instrumentalist, where the way to produce a sound from the instrument requires dexterity, skill and a degree of coaxing.

By the end of the 1970s, memory stores for the rapid recall of front panel settings had begun to appear, and by the end of the 1980s almost all monophonic synthesizers were equipped with memories. Front panels began to reflect this change by concentrating more on simplifying both the recall of memories and making simple minor edits to them. Many synthesizers became simply replay machines for preset sounds and for many users, their programming changed from being part of the performance art to being an unwanted chore.

By the late 1990s, live editing of sounds had become fashionable again, and synthesizer design reflected this with an increasing number of designs that included more controllers. In the first years of the twenty-first century, a number of manufacturers released synthesizers which were modern recreations of their own instruments from about 20 years before, but with memories and additional performance controls.

The performance controls on monophonic analogue synthesizers are mono-oriented: pitch-bend (often set to an interval of a fifth or an octave); octave switch (up or down, one or two octaves: often to compensate for a small keyboard span); modulation (normally vibrato) and occasionally, after-touch (normally controlling vibrato). For those instruments that do have front panel controls, they can be used as an additional method of control: real-time changes to sounds can be made 'live'.

This usage of front panel and performance controls arises from the monophonic nature of the keyboard. For a right-handed player, the right hand is used to play the keyboard, whilst the left hand is used to provide additional expression by manipulating the pitch-bend and modulation wheels. 'Classical' two-handed static position techniques for playing monophonic melodies are rarely seen; and instead, a flowing right-hand movement with lots of crossovers is used, thus freeing the left hand for the performance controls. Left-handed versions of monophonic synthesizers are very rare indeed: the placement of the performance controls is invariably on the left side of the keyboard (Figure 3.6.3).

FIGURE 3.6.3 A summary of the main features of a typical analogue monophonic synthesizer of the 1970s.