As an LFO crosses into the audio range it stops being perceptible parameter movement and starts creating sidebands

A low-frequency oscillator (LFO), also called a control oscillator, runs below audio rate (typically under ~20–30 Hz) and its output is routed to a control parameter rather than to the audio output: oscillator frequency (vibrato), amplitude (tremolo), filter cutoff (wah-like or ‘breathing’ motion), pulse width, or panning. Its waveform sets the modulation shape (smooth sine vs. stepped square), its rate sets the speed, and its depth sets how far the target parameter swings. The key boundary condition: when the LFO’s rate rises past roughly 20 Hz into the audio range, the ear can no longer track individual cycles as movement — instead the modulation begins generating new spectral components (sidebands), i.e. amplitude modulation (AM) sidebands or FM. So the very same oscillator routed to the same target is a slow ‘wobble’ at low rates and a source of new timbre/pitch content at audio rates; there is a continuous transition, not a separate mechanism. This is why ‘LFO’ names a role (control-rate modulator) more than a fixed frequency band.

Examples

Sine LFO at 5 Hz on filter cutoff: slow organic sweep; at 0.2 Hz: a meditative slow breath; sped to a ‘wobble bass’ around 5 Hz. LFO at ~80–220 Hz on amplitude/cutoff: AM sidebands appear as new pitches around the carrier rather than perceptible wobble. Vibrato = sine LFO ~6 Hz, ±50 cents on a 440 Hz carrier.

Assessment

For a 440 Hz carrier with a 6 Hz sine LFO at ±50 cents depth, give the resulting pitch range and state which target you’d change to get tremolo instead. Then explain what happens sonically, and why, as the LFO rate is raised past ~20 Hz into the audio range.