History: What is a microphone preamp?

What is a microphone preamp?

• A device that changes the array of integers back into an analog signal.
  This is the computer sound card's job.
• A device where the air molecules are spaced apart.
  This is rarefaction.
• A device that samples the analog waveform from the microphone.
  This is the converters definition.
• A device that provides electric current to the microphone to operate.
  Good job!