update README

README.md

@@ -68,6 +68,17 @@ Two independent LFOs per voice, each with:
 - Phase resets on note-on
 - Pitch modulation range: ±12 semitones
 
+## Arpeggiator
+
+Tempo-synced arpeggiator that sequences held notes into rhythmic patterns. Pure note-logic - no audio path changes.
+
+- **On/Off**: Enables the arpeggiator and routes incoming MIDI notes through it
+- **7 patterns**: Up, Down, UpDown, DownUp, Random, As Played, Chord
+- **Octaves**: 1 – 3 (extends the pitch pool above or below the root, clamped to MIDI range)
+- **Direction**: Up or Down for octave extension
+- **Rate**: 1/16, 1/8, 1/4, 1/2, 1, 2 (note-value divisions, tempo-synced via BPM)
+- Tracks held notes in press order (used by the As Played pattern)
+
 ## Effects Chain
 
 All effects are stereo and processed in series after the synth voice.
@@ -168,6 +179,7 @@ Custom dark theme with gold accents. ~50 knobs across 9 sections.
 | LFO 1/2 | Rate, Depth knobs, Shape and Destination selectors |
 | Delay | Time, Feedback, Mix knobs, Ping-Pong selector, Spread knob |
 | Reverb | Size, Damping, Mix knobs |
+| Arpeggiator | On, Pattern, Octaves, Direction, Rate selectors |
 
 ### Visualizers