well an lfo (low-freq operator) goes at a certain rate, usually measured in Hz. If your LFO is independent of tempo, you can set it to any rate you like. Many synths and samplers will allow you to sync the lfo to tempo, meaning that the LFO's rate is no longer independent, instead it will be a fraction or multiple of the MIDI tempo. So a free lfo would have settings like 10 Hz or 6.3 Hz, but a tempo-synced lfo would have settings of like 1/1, 1/8, or 2/1, referring to how many cycles per beat. This is useful for rhythmic modulation effects.
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