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 answer is "Diaphragm".

Explanation:

The lack of technology that historically prevented sound processing from using an electromagnetic recording system, that has a device capable of codifying electrical impulses.

answer; i believe the correct answer is layers;

the major difference between the two is the objective and the reward of the game. candy crush has a puzzle theme with the objective of meeting a specific quota of points or objects, you are able to gain access to the next level and compete with peers on the process. on duolingo the objective is rather different, you are given sets of questions for you to answer for you to move to the next level and as for the reward, you are able to learn available language as this is an app developed to teach the user about other languages.