Filtering an LFO with a lowpass filter smooths abrupt transitions and removes click artifacts

A square-wave LFO (e.g., for panning between two channels) produces instantaneous jumps in value, which can generate audible clicks or pops because the signal path cannot handle infinite-rate changes. Inserting a lowpass filter between the LFO and its destination smooths these transitions: the filter rounds off the sharp corners, converting step changes into gliding movements. The filter cutoff sets the smoothing time — lower cutoff means slower, smoother transitions. This technique is general: any parameter change that clicks can be smoothed with a one-pole lowpass filter (onepole~ in Max) or a line~ envelope segment.

Examples

Square LFO at 0.5 Hz driving a stereo pan in Max: add onepole~ 20 (20 Hz cutoff) after the LFO. The pan now glides between left and right instead of snapping instantly.

Assessment

Describe two synthesis scenarios where a one-pole lowpass filter would be used for smoothing rather than as a tone filter, and explain why smoothing is needed in each case.