History: What is sound quantification?

What is sound quantification?

• The process of changing the array of integers back into an analog signal.
  This is the computer sound card's job.
• The process of creating changes in pressure in the air to create sound.
  This is the speaker's job.
• The process of measuring the continuous analog signal at regular intervals and converting the samples to integers representing the amplitude.
  Yes!
• The process of providing electric current to the microphone to operate.
  This is a preamp's job.