Chorus
Color category, instrument-level.
Copies the signal, detunes the copies slightly, and plays them alongside the original. One instrument starts to sound like several.
Controls
Depth. How much the copies drift in pitch. Turned down you get a gentle thickening, wider and richer with no obvious movement. Turned up the pitch wanders audibly, which sounds lush on sustained chords and pads and unstable on a fast melodic line.
Mix. Balances the detuned copies against the original. With the original dominant you keep a lead focused and add a hint of width. With the copies as loud as the source you get a dense, ensemble sound. On bass, keep the copies well back or the low end turns blurry.
Presets
Subtle, Lush, Ensemble, Vintage.
When to use it
Clean guitar, synth pads, strings and electric piano. Sparingly on bass, rarely on drums.