History: What does the ratio of a compressor do?

What does the ratio of a compressor do?

• Ratio impacts how quickly the compressor will respond to changes in amplitude.
  That is attack and release.
• We will reduce any amplitude over the ratio.
  That is threshold, not ratio.
• A ratio is a collection of individual compressors for specific frequency ranges.
  That is a multipressor.
• The ratio determines how much we will reduce the amplitudes over the threshold.
  Great work!