Yamaha MX88 88 Key Weighted Action Synthesizer Yamaha Portable Keyboards PIANO TOUCHThe MX88 features a Graded Hammer Standard (GHS) weighted action. GHS weighted action has a heavier response in the low keys
Yamaha MX88 Keyboard – Stage Sound
Yamaha MX 88 Synthesizer – Woodsy's Music
Yamaha's MX88 synth turns your iPhone into a real instrument | Engadget