1.12 LFOs

Using LFOs

  • An LFO is a low frequency oscillator
  • The frequencies used are below 20Hz, so they are inaudible
  • An LFO changes a parameter of an effect or processor according to another wave
  • Examples might be altering the delay time according to a sine wave. Other geometric waves can be used to change the effect of an LFO (e.g. square/triangle/pulse)


Controls on Modulation Effects

  • Modulation effects have controls related to the rate and the depth of the modulation
  • Rate is how fast the periodic change of the parameter takes place (wave frequency)
  • Depth is how much the parameter is varied (wave amplitude)
  • The combination of both of these parameters can change whether the effect sounds subtle or very obvious


Comb Filtering


  • A comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference.
  • The frequency response of a comb filter consists of a series of regularly spaced notches, giving the appearance of a comb.


Historical Production of Modulation Effects


Leslie Speaker


  • The Leslie speaker uses the Doppler Effect to create modulation, and is sometimes called ‘Rotary’ on effect plugins.
  • This is similar to the changing pitch heard when an ambulance passes you
  • It is a system of rotating speakers used primarily with the Hammond Organ in the 1960s
  • It occurs because the source of a sound changes position, relative to the listener.

The Eagles – Hotel California

The Beatles – Let It Be

Tape-Based Origins of Modulation Effects

  • Modulation effects were originally created by using two tape recorders



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