4 paged synthesizer
page 1: filter with filtertype (lowpass, hipass, bandpass, bob and moog), cutoff, resonance and distortion
page 2: envelope with attack, decay, sustain and release
page 3: osc1 with osc type (sinus, sawtooth, pulse), volume, octave and vibrato
page 4: osc1 with osc type (sinus, sawtooth, pulse), volume, octave and vibrato

Inspired by the MFB Synth lite

still open:
* restore knob values from file
* label envelope
* flatten knob input