Utilities

Logic

Boolean logic for gates - AND, OR, XOR, comparators, and a flip-flop in one panel.

What is a Logic?

A logic module performs the basic operations of Boolean algebra on gate and trigger signals. It takes two gate inputs, treats each as either HIGH (true, voltage above threshold) or LOW (false, voltage below), and produces output gates whose state follows a logic rule: AND is HIGH only when both inputs are HIGH, OR is HIGH when either is HIGH, XOR is HIGH when exactly one is HIGH but not both, and NOT inverts a single input.

The reason logic matters in modular synthesis is rhythmic combination. Two simple clock patterns - say a steady eighth-note pulse and a separate Euclidean rhythm of three pulses spread over eight - can be combined through logic gates into much richer patterns. AND produces a pulse only on beats where both rhythms coincide (sparse, accented). OR produces a pulse on beats where either fires (dense, layered). XOR produces a pulse only on beats where they disagree (alternating, syncopated). One pair of inputs, three completely different rhythms.

Boolean logic was first applied to electronic music in the 1960s - early Buchla and EMS systems included logic processors specifically for this kind of rhythmic generative work. It remains one of the most musically generative tools in a modular system: a Euclidean ANDed with another Euclidean of a different prime length produces aperiodic patterns whose repeat cycle is the product of the two lengths - so two 16-step Euclideans whose lengths are coprime can combine into a pattern that doesn't repeat for ~256 beats.

Most logic modules also include a comparator (HIGH when input voltage A is greater than input voltage B - the analog cousin of digital logic) and a flip-flop (a single-bit memory that toggles state on each rising edge - which makes it a divide-by-two clock divider with a flick of patching). All of these together form a small toolkit for translating between the rhythmic, the random, and the structural domains of a patch.

Our Logic

Our Logic packs everything in one panel: all eight Boolean operations (NOT A, NOT B, OR, NOR, AND, NAND, XOR, XNOR) generated in parallel from the same two inputs, plus the two analog comparator gates (A>B, A<B) and a toggle flip-flop. Eleven outputs from one pair of inputs - patch any of them, ignore the rest.

The B Gate button lets you manually force input B HIGH when nothing is patched there - useful for testing logic relationships without having to wire up a second clock just to see what happens. The standard Eurorack 2.5V threshold is used for boolean conversion; outputs are clean 0V/10V gates.

The A>B and A<B outputs treat their inputs as continuous CV rather than boolean - so this single module is also a dual analog comparator, the way Doepfer A-167 or Joranalogue Compare 2 work. Sweep an LFO past a constant offset and these outputs fire gates wherever the curves cross. The FLIP toggle output gives you a divide-by-two on input A for free.

In a patch

The canonical generative patch: two Euclidean rhythm generators running at different lengths and densities, both patched into a Logic module. Take the AND output for sparse accents, the OR output for a dense backbone, the XOR output for syncopation. Drive three different drum voices (Bass, Snare, Hi-Hat) from the three logic outputs and a complete drum pattern emerges from two simple rhythms and a logic module.

Comparators turn continuous CV into rhythm. An LFO sweeping past a threshold, an envelope rising past a knee point, an audio signal peaking above a level - all become gate signals once they pass through a comparator. This is how you make a VCA open every time a particular note in a melody plays, or how a side-chain duck triggers from an audio signal's level.

The flip-flop is everywhere in clock work. Patch a clock into A; the toggle output is ÷2. Patch that toggle into the next flip-flop's A; you get ÷4. The whole clock divider family of patches is just chained flip-flops. It's also a tap-tempo memory - press B button, then trigger A repeatedly, and the toggle remembers which state it landed in.

Inputs

A (gate) — Gate input A. Standard gate threshold (2.5V). Also drives the toggle flip-flop on rising edges.
B (gate) — Gate input B. When unpatched, use the B button to manually set this high or low.

Outputs

NOT A (gate) — Inverted A. High when A is low, low when A is high.
NOT B (gate) — Inverted B. High when B is low, low when B is high.
OR (gate) — High when A or B (or both) are high. The most inclusive combination - fires on any activity.
NOR (gate) — High only when both A and B are low. The opposite of OR.
AND (gate) — High only when both A and B are high simultaneously. Use to find where two rhythms overlap.
NAND (gate) — High whenever AND is low. Fires on every beat except the overlap.
XOR (gate) — High when exactly one input is high, but not both. Creates syncopated rhythms by finding differences.
XNOR (gate) — High when both inputs match (both high or both low). The opposite of XOR.
A>B (gate) — CV comparator - high when A voltage is greater than B voltage. Works on full voltage range, not just boolean.
A<B (gate) — CV comparator - high when A voltage is less than B voltage.
FLIP (gate) — Toggle flip-flop. Changes state on each rising edge of A. Effectively a /2 clock divider when A is a clock.

Controls

B Gate — Manual gate for input B. When B has nothing patched, this button sets B high (10V) or low (0V).

Inspired by

The standard digital logic toolbox lifted into the modular world: every common boolean operation between two gate inputs, plus analog comparator outputs and a divide-by-two toggle for clock work.

Doepfer A-166 Logic
Joranalogue Compare 2
classic AND/OR/XOR logic for gates

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