History: What does the "Q" parameter do?

What does the "Q" parameter do?

• Q is the frequency or frequencies where the filtering will begin to occur.
  That is cutoff.
• Q is the amount of amplitude that we will impact.
  That is gain.
• Q is not a filtering parameter.
  Not correct.
• Q determines how smooth the transition is from unfiltered to filtered content.
  Yay!