lfo

An LFO is a kind of oscillator whose frequency parameter is restricted to the sub-audible band (conventionally 0.01-20 Hz): same construct, same two operating mechanisms (sustained periodic output from steady power), one narrowed parameter range. Nearest kind (Law 11e): there is no middle rung between 'low-frequency oscillator' and 'oscillator' — the LFO is the oscillator with the low-frequency constraint. Pinned sense (Law 11d): the is-a relation, not a dependency — an LFO stops being an LFO only when it stops oscillating, which is its identity as a kind of oscillator. specific->general direction (Law 9).

An LFO is built to serve modulation: its sole purpose is to generate a low-frequency control signal that modulates (varies over time) parameters of other audio elements — filter cutoff, amplitude, pitch. The LFO exists by design to make modulation possible in synthesis systems.

Removal test (Laws 2b/8b): remove the LFO and the periodic pitch variation disappears — without the low-frequency oscillator modulating the source's pitch there is only static pitch, not vibrato. The LFO definition names exactly this use: 'pitch (vibrato)' alongside 'amplitude (tremolo)', 'gain (ring modulation)', 'delay time (flanger)'. This is the pitch-domain twin of the ALREADY ACCEPTED tremolo DEPENDS_ON lfo edge — same pattern, different pair, completing the LFO's four named uses. Not merely 'sayable about' (ambient): the LFO is the operative component generating the effect's defining parameter variation. Direction tested: vibrato (dependent) → lfo (dependency).

Removal test (Laws 8a/8b): the phaser definition states 'An LFO modulates the all-pass filter parameters, sweeping the notches through the spectrum.' Without the LFO, the phaser reduces to a static all-pass phase-shift — no sweeping, no comb-filter swoosh. The LFO is constitutive to the phaser's operation, not optional. Pinned sense: LFO as the modulator driving the phaser's time-varying notches. Direction: phaser (dependent) → lfo (dependency).

Removal test (Laws 8a/8b): chorus definition states it 'applies a low-frequency oscillator to vary the pitch (typically ±5–20 cents) and delay time (typically 15–40 ms) of each copy.' Without the LFO, chorus has no modulation — the copies are static, producing no thickening or shimmering effect. The LFO is constitutive to chorus operation. Pinned sense: LFO as the modulator varying pitch and delay time in the chorus algorithm. Direction: chorus (dependent) → lfo (dependency).

Flanger uses LFO to modulate the delay time of its feedback loop — this oscillation IS the flanging effect. Remove the LFO and the flanger stops producing its characteristic sweeping sound. The removal test passes: without lfo operating now, flanger ceases its function.

Tremolo cannot operate without an LFO: its defining mechanism IS an LFO generating a periodic waveform that modulates amplitude. Remove the LFO — the periodic amplitude variation that constitutes tremolo disappears. The LFO is the signal source that tremolo depends on for its core operation, not merely a tool it optionally uses.