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Sequencing Without Sequencers

Exploring Clocks and Logic

Perfect Circuit · 07/22/20

Who doesn't like a good sequencer? Automating musical events has become such an important part of electronic music making, that it is difficult to imagine a setup void of at least one sequencer. Picking the right sequencer for your modular system is often as important as choosing the perfect match of filters and oscillators.

On the contrary, utility modules like clocks, switches, logic modules, and others are often overlooked, and at best saved for last. However, having access to those low-level utilities provides a lot of potential not only for adding subtlety to your patches, but also for opening up creative possibilities for composition and performance. For example, using clocks and logic modules can present a very robust alternative to step sequencing. This was the subject of our recent livestream tutorial with omiindustriies, and as an extension, will be the focus of this article.

Tick Tock Goes The Clock

In the jargon of electronic music, clocks are evenly spaced pulse signals that can be used for a variety of purposes such as initiating and synchronizing events, driving sequences, and, in some cases as audio signals. It is common to have several clock sources within the same synthesizer, as it helps to create variety and complexity by establishing and manipulating several musical timelines simultaneously.

To extract temporally related pulses that run at different rates, we often use clock dividers and multipliers. Clock dividers create slower clock signals by dividing the rate of incoming pulses, and multipliers do exactly the opposite. As Naomi demonstrates in the video tutorial, having such a wide range of related pulse signals is very useful for creating rhythmic sequences. To do that, all you need is to spread out various clock signals to taste across your patch. You can use them to trigger drum modules, and voices, crudely open VCAs, and with some processing, these pulses can even be used directly as sound sources.

Which clock dividers/multipliers (or as a macro-term, clock-modulators) you use in your system can significantly impact your workflow and musical results. For example, something rudimentary like Doepfer's A-160-1 simply takes the incoming clock signal and provides six divided clock outputs with rates predetermined by design; 4ms Quad Clock Distributor, on the other hand, lets the user set the div/mult value using a knob or control voltage signal; the ALM Pamela's New Workout lets you manually dial precise division/multiplication values per output; Make Noise's Tempi offers a tap-tempo like interface for manually setting the clock rates per output, as well as some more esoteric options for mutating clock rates, and swapping clocks across selected channels.

Switch It Up

Another useful tool for creative sequencing in a modular synthesizer is a sequential switch. It can come in a few different forms—either by dynamically distributing several input signals across a single output or the opposite, by dispensing a single input signal across multiple outputs. The more advanced iteration of this functionality is a sequential switch matrix, where multiple inputs can be assigned to multiple outputs.

Sending a gate into the trigger input of the sequential switch facilitates the rerouting of the signal from one input/output to another sequentially. Depending on the module, this could also be done using a dedicated knob or a control voltage.

Let's Be Logical

Logic functions are abundant in synthesizers and music software, but they are often hidden under the hood and thus remain relatively underexplored as composition and performance tools. Modular synthesizers and software frameworks like Pure Data and Max/MSP make logic easily accessible to musicians. Those interested in generative music systems will greatly appreciate logic modules, as they can also be very efficient in fostering happy accidents and unexpected rhythmic structures. There are a few different types of logic implementation, however the core principle of all lies in comparison between two or more signals, which based on certain rules affects the output.

Boolean logic modules operate in the digital domain, comparing and outputting strictly binary signals. There are six types of boolean logic operators: AND, NAND, OR, NOR, XOR, XNOR. The truth table attached should provide a good visual reference for inputs/output relationship. Omiindusriies' Ilyana was specifically designed to host various boolean logic functions under one panel. Sending slow clock signals into it and spreading the outputs to trigger various musical events in your patch can be very useful for creating ever-evolving movement within your composition. In contrast, sending faster pulses into Ilyana turns it into a powerful gate sequencer capable of unpredictable twists and turns.

Comparators weigh the input signal against a reference voltage and output a square wave if the input hits the threshold. The threshold is set by a parameter knob, and in some cases it can be dynamically controlled by voltage. Gating events at a specific voltage level is a good trick to spice up your sequences.

Finally, there are analog logic modules which are designed to compare continuous signals and output specific voltages based on the selected logic function, such as the minimum, maximum or sum of voltages. Analog logic can be useful for creating modulation signals or melodic sequences (when paired with a quantizer).

If you ever wondered why Make Noise Maths is such a popular module, well it is because it can do all of the above and more.

ADC/DAC

A particularly uncommon method of creating sequences involves using analog to digital and digital to analog converters. Examples of such would be the incredibly flexible and multifaceted combo from XAOC Devices Drezno +Lipsk, and the latest module from omiindustriies r2rawr which takes in up to five gate signals and uses a DAC to convert them into a continuous sequence.

At their core, these modules accept multiple gate inputs and mix them together to create a weighted sum—combining multiple digital (on/off) signals into an analog (continuous) signal, hence the term Digital to Analog Converter. Similarly, some devices can perform the opposite function, converting analog voltages into multiple streams of binary signals, which can be used as clock sources and more.

As you may have guessed, there are many more applications to logic modules than it is possible to cover within the scope of this article or video tutorial. No doubt we will be coming back to this topic in future. For now, please make sure to check out the excellent tutorial from Naomi and her Signal article for an even deeper perspective on the subject.