Delay Effects

Delay Effects

• One capability of computers that we haven't talked about much is the ability to store a signal and give back a delayed copy of it

• This is pretty much unobtanium for analog systems. Digital delay is crazily cheap and good

• Amount of delay determines effect

  • Small delay (< 10ms): Phase cancellation, localization

  • Moderate delay (10-100ms): "Ensemble" effect (example)

  • Moderate to long delay (50-500ms): Reverb and echo effects

• Multiple delay effects can be combined; delayed signal can be chained with other effects

• Usually feed delayed signal back into input for reverb / echo effects

• Wet/dry is a big thing with delay effects, e.g. echo — how much reverb signal to feed through (wet) vs original signal (dry)

Ring Buffer

• Delay data structure is a queue of samples: typical implementation is a ring buffer

  len = 100
  buffer = [0]*len
  head = 0
  tail = 0
  empty = True
  
  def queue(s):
      assert empty or head != tail
      buffer[tail] = s
      tail = (tail + 1) % len
      empty = False
  
  def dequeue():
      assert not empty
      s = buffer[head]
      head = (head + 1) % len
      empty = head == tail
      return s
  

Effect: Reverb and Room Effects

• Idea: Signal + delayed copy simulating resonance and bouncing

• Typically longish delays (100ms+)

• Typically delayed copy is filtered and damped

• Output-to-input copy is pretty standard

• Really fancy 3D sound modeling is a thing: leads into general acoustics (study of physical sound)