Answer:
The missing piece of technology that prevented the audio production industry from using the electrical recording system earlier was a device that could amplify the electric signal. The device that made this possible was the Audion valve
Step-by-step explanation:
The telephone system in the passage is able to convert sound to electronic signals in a crude manner, without amplification. The electrical recording system, whereby a microphone converted sound into amplified electrical signals was, made possible by the invention of the electronic valve, known as the Audion triode vacuum tube by Lee De Forest in 1906. Electrical sound systems were built based on the Audion tube before transistor-based audio equipment became commercially available in the 1950s.