The telephone, invented in 1876, converted acoustic sound to electric signals. However, the audio production industry began using the electrical recording system only in 1925. Why was there a delay in using this technology in audio production? The missing piece of technology that prevented the audio production industry from using the electrical recording system earlier was a device that could the electric signal. The device that made this possible was the .

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

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.