The term low frequency oscillation or "LFO" is used to describe any periodic changes to a signal, where the frequency of these changes is small (slow) enough to be distinct to the human perception.
Anything with frequency up to 10 Hz can be called "low frequency oscillation", since the changes made by such a frequency are slow enough to be noticeable (in audio, noticeable to the human ear). Examples include:
- The change in high-frequency gain in a wah wah effect: A wah wah effect is an equalizer that increases the amplitude of high and then mid and low frequencies in an audio signal. The low frequency oscillation is the periodic movement of the gain across the frequency spectrum.
- Periodic channel pressure and key pressure changes in MIDI, such as when the user of a MIDI keyboard increases and decreases pressure on the keyboard keys. The low frequency oscillation can be implemented similarly to a wah wah effect or can include small changes in the pitch.
- Any other tremolo, such as when a guitar player uses the mechanical tremolo on the electric guitar. The low frequency oscillation is the periodic change in pitch produced by the tremolo.