Chapter 8: Strange but useful modules

Fantastic instruments can already be built with the modules considered so far. We have various sound generators, filters and other tools for shaping the sounds, mixers and modulation sources, as well as the important trigger/gate signals at our disposal. What is still missing are a number of very interesting tools with which we can manipulate our control voltages or our trigger and gate signals. How should one imagine this? In the case of control voltages, for example, abrupt changes can be smoothed out or continuous voltages can be limited to a few discrete values, LFO waveforms can be folded. Triggers can be delayed, inverted or linked together using logical operations, the frequency of regular clock triggers can be divided or multiplied, etc.

Processing of control voltages

Slew limiters

Slew limiters are the “classics” in this category. Slew limiters were already built into the first Moog systems, with which you could then create a portamento (i.e. a smoothing of the pitch) between two played notes. This effect is used very prominently in “Lucky Man” by Emerson, Lake & Palmer. Ultimately, a slew limiter is something like a simply built low-pass filter: Rapid changes (i.e. high frequencies) are rounded off.

Of course, the A-129 / 3 also belongs to the series of slew limiters (A-170, A-171). To be used as a slew limiter (5 channels, with synchronous control), the A-129 / 4 slew limiter controller is also required.


Quantizers are in some ways the opposite of slew limiters. Any voltage is rasterized by the quantizer to specific – musically desired – values. A classic application is in connection with an analogue sequencer. Here you want to be sure to set the pitches to a scale or triad without minimal changes to the sequencer potentiometers leading to “out of tune” results.

The A-156 Dual Quantizer is mostly used to generate control voltages for VCOs. But the use is also worthwhile with filters (if they are reasonably well calibrated to 1 V / octave). For example, you can quantize a random voltage and “tonally” modulate a filter with it – the effect becomes very clear with increasing self-resonance, but is also effective before that.

Waveshapers for control voltages

It will not come as a surprise that modules can be used here that are also suitable for audio signals and vice versa. Modular systems (with the exception of the systems from Buchla) usually do not differentiate between audio and control voltage anyway, apart from a few physical restrictions. Slew limiters and quantizers can work with any control voltage. For waveshapers, on the other hand, LFOs are the most interesting voltage source due to the principle involved.

The following waveshapers / wave-multipliers are particularly worthwhile: A-116, A-136, A-137-1 and A-137-2. You can conjure up highly complex waveforms from a simple LFO signal, which are ideal for modulations in drones and effects. As with the use of audio, it also applies here that the waveshaper can only do little, if anything with square/pulse as input material.

Combine control voltages creatively

Two or more control voltages (e.g. several LFOs) can be mixed together to get a more complex modulation signal. There are also a number of modules that combine multiple signals in quite creative ways. These can be ring modulators, max/min circuits, a comparator or even track & hold or sample & hold circuits.

Posts on modules that process control voltages

Changing trigger and gate signals

Triggers and gates – length matters

A basic way of manipulating trigger and gate signals is to change the length of the signal (which, of course, only makes sense when used as a gate). The conversion of short trigger signals into longer gate signals or vice versa, as well as the delay of triggers by a constant amount, also belong here.

Such a transformation can be a delay (A-162), conversion of triggers into (longer) gate signals (A-162, A-142-1) or vice versa (A-165), a logical combination of gate signals or triggers (A-166, A-186-1), or simply an inversion of “on” and “off” in gate signals (A-165, A-166).

Several triggers meet

In the simplest variant, a trigger signal is generated at the output of the module for each trigger signal at one of the inputs. Exactly simultaneous triggers remain a single trigger and overlapping gates become a single longer gate.

Logical operations such as “AND”, “OR”, “XOR” etc. are much more sophisticated – but also require a little more mental preparation. A very banal inversion of a gate signal requires only a single input signal, but it is also a logical operation – “NOT”.

Creating gates from other signals

The A-167 Analog Comparator was already presented in the modules for control voltages, it can generate gate signals from “normal” control voltages. The A-119 External Input / Envelope Follower module should also be mentioned here: it not only generates an envelope curve from an audio signal, but also a gate signal.

Rhythmic manipulation

A large and exciting field is the rhythmic manipulation of periodic trigger signals, so-called “clock” signals, such as those used to clock a sequencer. In the past there were only very simply structured frequency dividers, which then output a e.g. half-speed clock signal always on the respective second note, which unfortunately is not particularly “musical” in most cases. Doepfer now builds very tricky clock dividers that always output their divided signals on the first note of a bar and are perfect for more complex sequencer controls. A “clock multiplier” is also comparatively new, which can multiply an existing (tempo-stable!) clock signal. This also works via voltage control, for example to reproduce the “ratcheting” sequences known from Tangerine Dream.

More modules to change triggers

A whole range of other modules, of which one does not necessarily expect this, are very well suited for manipulating triggers and gates, as well as for clock signals (which are also only regular triggers for synchronous control of sequencers).

A-142: Swords into ploughshares, triggers to gates

The A-142-1 Voltage Controlled Decay / Gate is not just an envelope generator, but a nice tool to convert trigger signals into gate signals. Die Länge des Gatesignals ist abhängig von der Decay-Länge und dem Threshold-Wert (beides manuell per Regler einstellbar). A trigger signal at the “Trig. In” generates a gate signal at the “Gate Out” output or a logically inverted gate signal at the “Inverse Gate Out” output.

Division of clock signals

The frequency dividers A-113, A-160 and A-163 are all very well suited for dividing clock signals in order to create complex rhythmic structures. The A-113 Subharmonic Generator in particular is a powerful tool with its four independent and storable frequency dividers. In addition, various divider combinations can be called up during operation via gate signals (inputs “Foot Ctr. In 1” and “Foot Ctr. In 2”).

“Musical” division of clock signals

The A-151 switch and the luxuriously equipped A-152 are also extremely exciting when processing clock signals. They can be used to build clock dividers that work “musically”: the divided clock frequencies remain in sync with the original clock, i.e. they trigger on the first beat (and not on the last beat like an A-163). Appropriate patches are described for the two modules.

Rhythm is it

The sequencers A-155 and A-161 can create rhythmic patterns from clock signals by selecting which clock signal will also have a gate signal at the output or which will not.

Random beats

The random generators A-149-1 and A-149-2, as well as A-117 have a clock input, which enables the generation of random triggers within the clock grid.

Posts on individual modules that change triggers/gates