When was the synthesizer keyboard invented?
Synthesizer
1876
One of the earliest electric musical instruments, the Musical Telegraph, was invented in 1876 by American electrical engineer Elisha Gray. He accidentally discovered the sound generation from a self-vibrating electromechanical circuit, and invented a basic single-note oscillator. This instrument used steel reeds with oscillations created by electromagnets transmitted over a telegraph line.  Gray also built a simple loudspeaker device into later models, consisting of a vibrating diaphragm in a magnetic field, to make the oscillator audible.[3][4] This instrument was a remote electromechanical musical instrument that used telegraphy and electric buzzers that generated fixed timbre sound. Though it lacked an arbitrary sound-synthesis function, some have erroneously called it the first synthesizer.[1][2]