- 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
- 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
- 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