History: What are the common parameters of tremolo?

What are the common parameters of tremolo?

• Amplitude and frequency.
  Close, but think about what a tremolo does.
• Wet/dry mix, delay time, depth, & rate.
  You may see delay time and wet/dry mix on some tremolo effects, but I wouldn't say they are common.
• Rate and depth.
  Correct!
• Phase and spectrum.
  This is not correct.