The LFO is a basic concept for shaping how sounds are voiced, how they move, and how they layer in synthesizers and MIDI instruments. It is your way into deliberately adjusting the changes in a sound that are hard to grasp when you only pick presets.
What it does
Using an LFO lets you shape not only the tone itself but also its change over time and the impression of the performance. Start by moving a single setting little by little and listening for which change you can hear.
Relationship to the synthesizer
On most synthesizers it is used in combination with the oscillator, filter, and amplifier. Names and displays differ between models, but organizing them by role, that is generating, shaping, and changing the sound, makes them easier to understand.
Playing and MIDI
Combined with notes entered from a MIDI keyboard or the piano roll, it lets you create expression and rhythmic variation. Anything that can be automated can also be moved along with the song’s development.
Care when adjusting
Larger values make the effect obvious, but they also change level, placement in the stereo field, and how the part overlaps with other instruments. Compare on and off in the full mix, not just soloed.
Where to start
Pick a preset first, then adjust a single parameter from a state that is already close to the sound you want. Noting your changes and keeping a way back makes it easier to judge.
The basics of checking
Controls differ from instrument to instrument. The shared fundamentals are covered in the software instrument article.
