This is the VODER, or Voice Operation DEmonstratoR, produced by Bell Labs. From Wikipedia (because it explains well and I’m lazy):
The Voder synthesized human speech by imitating the effects of the human vocal tract. The operator could select one of two basic sounds by using a wrist bar. A buzz tone generated by a relaxation oscillator produced the voiced vowels and nasal sounds, with the pitch controlled by a foot pedal. A hissing noise produced by a gas discharge tube created the sibilants (voiceless fricative sounds). These initial sounds were passed through a bank of 10 band pass filters that were selected by keys; their outputs were combined, amplified and fed to a loudspeaker. The filters were controlled by a set of keys and a foot pedal to convert the hisses and tones into vowels, consonants, and inflections. Additional special keys were provided to make the plosive sounds such as “p” or “d”, and the affrictive sounds of the “j” in “jaw” and the “ch” in “cheese”. This was a complex machine to operate. After months of practice, a trained operator could produce recognizable speech.
This device was demonstrated at the World’s Fair in New York in 1939 and at the Golden Gate International Exposition