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)

Last modified: Tuesday, 28 April 2020, 1:05 PM