via this auction
"The SK30 and SK50D also feature a SOLO SYNTHESIZER SECTION which is a single VCO driven mono-synth similar to a Roland SH-101. It has basic pitch, waveform, filter, volume, envelope generator and portamento functions. The keyboard's after-touch can control the vibrato, tremolo, and brilliance effects. You can effectively play leads in the solo section while simultaneously playing chords in the string, organ or poly-synth section"
