Final answer:
The specific technology used in the RCA synthesizer is the vacuum tube.
Step-by-step explanation:
The specific technology used in the RCA synthesizer is the vacuum tube. The vacuum tube, specifically the triode vacuum tube, was patented in 1906 by Lee De Forest. It became the basis of radio transmitters and receivers, including the synthesizer. The vacuum tube technology allowed for the amplification of the audio signal to drive a speaker or be recorded.