press [synth] to enter synthesizer mode

use T1-T4 to access different screens:
- T1: synthesis engine (change the sound type)
- T2: envelope (ADSR shape)
- T3: effect (per-synth effect)
- T4: LFO (modulation)

turn the colored encoders to adjust parameters
each encoder matches the color on screen

hold [shift] + turn encoder for fine control