Mixing & Output

Fade

A two-in / two-out crossfader for blending audio or CV signals - manually or under voltage control.

What is a Fade?

A crossfader is a two-input, two-output module that smoothly blends between its sources under manual or voltage control. At one extreme of the fade, input 1 dominates; at the other, input 2 takes over; in the middle, you hear an equal mix of both. The fader sweeps a continuous transition - no clicks, no jumps - between two signals. It is the same idea as a DJ mixer's crossfader, miniaturised down to a Eurorack panel and made voltage-controllable.

Crossfaders matter because *transitions* are how musical sounds evolve. Hard cuts between timbres feel mechanical; smooth blends feel intentional. With a crossfader you can morph between two oscillator waveforms while a melody plays, swap between dry and processed signals to create a wet/dry knob for any effect, or swing between two filter outputs for hybrid filter behaviour. Modulate the fade position with an LFO and the patch is constantly evolving without you touching anything.

The math is simple linear interpolation: OUT = IN1 * (1 - fade) + IN2 * fade. With a -6dB pan law the perceived loudness stays roughly constant across the sweep, even though both signals are at half-amplitude at the midpoint. A two-output crossfader does the *complementary* mix on the second output - what one output gives up, the other picks up - which makes it a stereo panner as well as a mono blender.

Our Fade

Ours is a two-input, two-output crossfader in 6 HP with a single fade knob and a CV input. The DSP is straightforward linear interpolation with -6dB pan law: OUT1 = IN1 * (1 - fade) + IN2 * fade, OUT2 = IN1 * fade + IN2 * (1 - fade). At fade 0 the inputs pass straight through (IN1 to OUT1, IN2 to OUT2). At fade 1 they swap. At fade 0.5 both outputs carry an equal mix.

The fade CV input adds +/-5V of modulation to the manual knob position, clamped to the 0-1 range. Patch a bipolar LFO and you can sweep the full range from a knob set at center; patch a unipolar envelope and it walks the fade up from rest. We do not equal-power scale (like a cosine pan law) - linear keeps the math predictable for CV signals as well as audio, which is the more common patching territory in modular.

There is no panel switch for audio versus CV mode because there does not need to be one - the same circuit handles both correctly. For more elaborate signal-routing (envelope-driven panning, three-way blends), reach for Warps. For mixing more than two sources at once, see the Stereo Mixer. Fade is the small, sharp tool: two signals, one knob, smooth movement between them.

In a patch

The two most common patches are *timbral morphing* and *dry/wet blending*. For morphing, run two oscillators (or two outputs of the same one - a saw and a square) into the inputs and modulate the fade with a slow LFO; the timbre evolves continuously through the patch. For dry/wet, send an unprocessed signal into one input and the same signal through a reverb, delay, or chorus into the other; the fade knob becomes a wet/dry control for any effect that lacks one.

Crossfaders also make great kill switches for performance: route your audio through one, hold the fade at 0, and a single CV pulse can swap to a second source - a pre-recorded loop, a looper output, a different patch entirely. Drive the CV from a manual gate and the crossfader becomes a dramatic transition tool.

On CV rather than audio, crossfaders blend modulation sources. Fade between two LFOs at different rates and you get a third LFO with a continuously variable shape. Fade between two sequencers and you can morph between two melodies in real time - the kind of Buchla-style timbral patching that needs no MIDI, no software, just voltages.

Inputs

IN 1 (audio) — First audio/CV input. At Fade=0 this routes entirely to OUT 1. At Fade=1 it routes entirely to OUT 2.
IN 2 (audio) — Second audio/CV input. At Fade=0 this routes entirely to OUT 2. At Fade=1 it routes entirely to OUT 1.
CV (cv) — Crossfade CV modulation input. +/-5V range added to the Fade knob position. Use an LFO for automatic sweeping.

Outputs

OUT 1 (audio) — First output. Receives a blend of both inputs based on the fade position.
OUT 2 (audio) — Second output. Receives the complementary blend - what OUT 1 does not get, OUT 2 does.

Controls

Fade — Crossfade position from 0% (hard left - signals pass straight through) to 100% (hard right - signals swap). 50% gives an equal mix on both outputs.

Inspired by

A classic two-input crossfader topology, equally at home on audio and CV. Linear -6dB pan law smoothly blends the two inputs across both outputs; CV input adds +/-5V modulation atop the manual fade position for automated morphing.

Make Noise X-Pan
Frap Tools 321
Intellijel Mixup

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