Keyboard synthesizers take all the modules needed to create a complete synth 'voice' and package them with a familiar control surface. This integration -- especially when paired with mod wheels, joysticks, or touch sensitive ribbons -- creates a highly-expressive instrument that's unified in its approach.
Important keyboard synthesizer features include velocity sensitivity, which changes the initial volume of a note the faster a key is pressed, while 'aftertouch' detects finger movement after the note has played. Piano players will appreciate weighted keys and 'graded hammer action', the latter of which gives a heavier response in the lower register and a lighter response up high.