sentences:  When the SY77 was released in late 1989, its initial prices were close to $3000 USD/£2000 GBP.In 1991, it was followed by the SY99, a successor that cost ~$4000/£3000 and expanded its capabilities with a 76-key keyboard, the ability to load user-specified samples for AWM, a more advanced effects unit, and other features.The AFM synthesis of the SY77 is effectively a superset of the 6-operator FM synthesis available on the Yamaha DX7 and DX7 II series of synthesizers.