Overtone
Hear the harmonic series — the natural intervals a vibrating string makes. The Arpeggiator's TUNING is set to SERIES, so instead of 12 equal-tempered notes it climbs the OVERTONES of the note you hold (f, 2f, 3f, 4f… — the octave, the twelfth, the double-octave), in PURE ratios that sit between the piano keys. Press play, then hold ONE note and listen to the ladder; hold a chord to climb higher. On the Arp, switch TUNING to JUST to re-tune a held chord to pure just-intonation thirds and fifths, or back to EQUAL for the usual 12 notes. A clean sine-ish voice so the partials ring true.