Move the level of a file up and down at a set rate. Slow settings breathe, faster ones pulse, and past about 10 Hz the modulation starts to be heard as a texture rather than as separate events.
Rate
The rate slider covers 0.1 Hz to 20 Hz on a log scale, so the slow end where most musical settings live gets most of the travel.
To line the pulse up with a tempo, divide the beats per minute by 60. At 100 BPM, 1.67 Hz is one pulse per beat and 3.33 Hz is one per eighth note. Nothing here follows a tempo map, so a track that drifts will drift away from the setting.
Depth
Depth is how far the level falls at the bottom of each cycle. At 50% the quiet part of the cycle is half the level of the loud part. At 100% it reaches silence, which is the chopping effect.
The peak of the cycle is always the original level, so raising depth makes the file quieter on average rather than louder.
Shapes
Sine rises and falls smoothly and is the least noticeable at any depth.
Triangle moves at a constant rate in each direction, which gives a more even pulse with a sharper turn at the top and bottom.
Square switches between the two levels. The edges are rounded over roughly 1.5 ms, because a genuine step in a gain curve is a click. That is short enough to still sound abrupt.
Stereo phase and auto-pan
The stereo phase control offsets the modulation between channels, from 0 to 180 degrees.
At 0 both sides move together and the whole image pulses. At 180 they move in opposition, so one channel is loudest exactly when the other is quietest, and the result is an auto-pan. Values in between move the image without fully leaving either side.
Example: a pad that needs motion
Rate 2 Hz, depth 40%, triangle, stereo phase 180 degrees.
The level never drops far enough to break the sustain, and the opposing channels keep the part moving across the field rather than pulsing at the listener.