Utilities

Compare

Window comparator - turn a continuous voltage into gates, mins, maxes, and rectified signals.

What is a Compare?

A comparator is a circuit that asks one question: is voltage A greater than voltage B? It outputs a gate - HIGH when yes, LOW when no. That single binary decision is the bridge between the continuous world (where modulars naturally live: smooth voltages, sweeping LFOs, gradual envelopes) and the discrete world (where rhythm and structure live: gates, triggers, on/off events).

A window comparator is the next step up. Instead of comparing two voltages, it asks: is voltage A inside the window between -B and +B? That gives you two complementary gates - one HIGH while inside the window, one HIGH while outside - and two shaped CV outputs: a clipped version of A that's been clamped into the window, and a limiter residual of whatever was clipped off. The clipped and residual signals always sum back to the original A; the window decomposes the input into its inside and outside parts.

Comparators turn continuous CV into rhythm. An LFO sweeping through a comparator with a fixed threshold generates a gate every time it crosses that threshold - effectively a clock at the LFO's rate derived from the LFO itself. A more interesting trick: feed an audio signal into the comparator and the gate output fires on every positive-going zero-crossing, giving you a pitch tracker that converts an instrument into clock pulses.

Window comparators add selectivity. The gate fires only when the input is within a chosen voltage range, which is musical when the input is a melody: a window centered on +1V (around C5) might gate only the highest notes in a sequence, leaving the lower ones silent. A second window on the same melody could gate only middle-register notes. With multiple windows, one melodic CV can control several voices, each playing only their assigned register.

The historical reference is Doepfer A-167 - a comparator with adjustable hysteresis - and Joranalogue Compare 2, which adds the window function and shaped outputs. Most analog synthesists treat comparators as background utilities, but they're one of the most generative modules in the rack: any continuous voltage becomes any pattern of triggers, given the right comparison.

Our Compare

Our Compare bundles ten outputs from two CV inputs: MAX, MIN, window CLIP/LIM, two window gates (CLP G and LIM G), simple comparator gates (A>B, A<B), ABS (rectifier), and DIFF (subtraction). One panel covers the entire family of analog comparator and arithmetic operations.

The B Offset knob (-10V to +10V) sets the threshold when B is unpatched, or biases B when patched - so you can sweep the comparison threshold without needing a CV mixer in front. A separate B CV input modulates the same offset, useful when you want the threshold itself to move under control of another envelope or LFO.

The window function is symmetric around zero - the window runs from - to +. So if you want the window centered somewhere other than zero, add a DC offset to A first using a Rescale or CV Mix. This keeps Compare's panel small and the math clean: one B input controls the window width, no separate center knob to fight.

In a patch

Patch an LFO into A and leave B at a fixed knob position. The A>B gate fires every time the LFO peak rises above the threshold; the A<B gate fires on the troughs. Patch the gate into an envelope's trigger and the envelope re-articulates on every cycle of the LFO - a continuous oscillation has been turned into a rhythmic pattern.

Window comparators excel at register-aware patches. Patch a melody CV from a step sequencer into A, set the window narrow around the middle register. The inside-window gate fires only on middle notes; patch it to a chorus send so middle notes get processed and high/low notes pass dry. The patch articulates differently depending on which register the melody is playing.

The ABS output is the simplest way to build an envelope follower: take an audio signal, run it through ABS to rectify it (negative half-cycles flipped positive), then through a slew limiter to smooth it. The result is a CV that tracks the audio's amplitude - patch it into a filter cutoff for an auto-wah effect, or into a VCA for ducking.

Inputs

A (cv) — Primary signal input. This is the signal being compared and processed.
B (cv) — Reference signal input. When unpatched, the B OFFSET knob sets the reference voltage directly.
B CV (cv) — CV modulation for the B offset. Adds to the B OFFSET knob value.

Outputs

MAX (cv) — Outputs whichever of A or B is higher at each moment. Useful for selecting the stronger of two envelopes.
MIN (cv) — Outputs whichever of A or B is lower. The complementary partner to MAX.
CLIP (cv) — Window clipper. Restricts signal A to the range -B to +B. Portions of A inside the window pass through; portions outside are clamped.
LIM (cv) — The complement of CLIP - outputs the portion of A that falls outside the -B to +B window. CLIP + LIM always equals A.
CLP G (gate) — Gate high when A is inside the -B to +B window.
LIM G (gate) — Gate high when A is outside the -B to +B window.
A>B (gate) — Gate high when A is greater than B. Works on full voltage range for precise threshold detection.
A<B (gate) — Gate high when A is less than B.
ABS (cv) — Full-wave rectifier of A. Flips all negative voltages positive (|A|). On audio, this doubles the frequency for an octave-up effect.
DIFF (cv) — Difference output: A minus B. Useful for envelope following, pitch tracking, or detecting divergence between two signals.

Controls

B Ofs — B offset voltage from -10V to +10V (default 5V). Sets the B reference when B is unpatched, or adds to B when patched.

Inspired by

A standard analog comparator extended with the usual utility outputs: max, min, window clip and limit, full-wave rectifier, and difference. Most modulars hide a comparator inside another module; here it is its own panel.

Doepfer A-167
Joranalogue Compare 2
classic analog comparator

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