Download Image For Larger View
Low Frequency Oscillator
The Low-Frequency Oscillator (LFO) is used as a controller to create certain effects.
Like a regular oscillator, the LFO creates a waveform; however the the frequency is below the range of human hearing-between 0.1 Hz and 20 Hz.
Although we cannot actually hear the LFO directly, we can hear its effect on another module.
When an LFO is set to a sine wave and used to control a VCO, the result is a continuous rise and fall in the pitch of the VCO = Vibrato
When the LFO controls a VCA=Tremolo, a continuous rise and fall in loudness.
LFO can control a filter causing a continuous fluctuation in timber between brighter and duller.
Typically, LFOs are set to either sine waves or triangle waves, but interesting effects can be gained by using other waveforms as well.
Square wave on LFO to modulate the sound source (VCO)=trill effect.
Rate=Determines the frequency of the LFO
Depth=Sets the amount of modulation
Delay=Allows the LFO modulation to be faded in to the audio module over time.
LFO is used to control or change the character of a sound source or modifier=Modulation
Vibrato and tremolo are two of the most common modulation effects.
On an analog synthesizer the keyboard sends out a voltage to the VCO.
The higher the key, the higher the voltage and thus the higher the pitch.
What happens to a waveform as its frequency gets higher?
A feature called key follow or keyboard tracking can also send this control signal to the filter. This will cause the sound to get brighter as the pitch rises or vibrato/tremolo gets faster in much the same way many acoustic instruments do.