Sound four voices at once and tune them by ear. Type each voice in hertz, or set a reference and stack integer ratios. Anchor the reference to the fundamental or hold the bass note fixed so every chord sounds in the same octave. Load a preset, then bend it.
Every note in the harmonic series above one fundamental, up to the 32nd harmonic. Tap harmonics on and off in different combinations to hear the chord qualities that emerge as you climb the series.