A Low Frequency Oscillator, LFO usually short, is a low-frequency oscillator, which is used in electronic musical instruments and effects processors for modulation sound-shaping components. It generates a low-frequency waveform (usually sinusoidal, triangle, square, sawtooth, or other well ) is thus often in the range below 10 Hz, and even for the earring imperceptible.
Falls below the lower limit of hearing the LFO frequency in the listening area creating a complex, stationary sound: a mixture of harmonic and inharmonic partials, which is the ratio of the two frequencies and their amplitudes dependent. The partials arise in the known from the ring modulator manner by the formation of sum and difference frequencies: the modulation frequency B is the fundamental frequency of the sound A both added and subtracted from it. It is a Ringmodulationsperfektionierung.
A particular advantage of this sound synthesis method relates to the relatively easy creation of dynamic sound spectra. If the overlay with the modulation signal is not continuous but is controlled in their chronological sequence, the generated sound is slowly changing. The timing of the sound change can be realized by assigning proprietary envelopes for modulation or carrier frequency. Sudden changes in sound between different stationary states in themselves sound can be achieved are by at specified times modulation frequencies by potentiometer and switch, or automatically ( by a sequencer) on or off.
A special case occurs when sound and modulation frequencies even results previously performed amplitude modulations. This is called different modulation levels. With these very complex sound results can be generated, which are mathematically very difficult to calculate.
By linking multiple modulation levels, it is possible with moderate effort, the structure of the resulting sounds vorherzuberechnen. This arrangement of the modulation is an essential part of musical planning and thus comparable in many respects traditional scores.
Some LFOs have their own envelope, the modulation depth is controlled. So you can adjust the rise and fall of a modulation effect, such as the slow swelling of the vibrato of a violin.
In some synthesizers, assigning the LFO comes at a sound-shaping component means a fixed predetermined shortcuts or a modulation matrix. It is also possible to use a VCO as LFO to use ( see the old Moog synthesizers).
Examples of use: