Gate

An envelope follower measures the signal's amplitude, and that measurement is compared against the threshold. Above it the gate is open and audio passes; below it the gate closes and the output is silence. It is not a filter and it removes nothing from inside a note, it only decides, moment to moment, whether there is a note at all.

Smoothing is the follower's time constant, and it is the one control that decides whether this sounds like a gate or like a fault. Because the same constant governs opening and closing, a setting fast enough to catch a transient is also fast enough to chatter when the signal sits near the threshold, and a setting slow enough to be smooth will let the tail of a note through the gap after it.

The browser preview builds this from four plain nodes and no worklet. A waveshaper rectifies the input, a one-pole lowpass whose cutoff is 1/(2·pi·Smoothing) averages it into an envelope, a second waveshaper maps that envelope through a soft-knee curve, 0 well below the threshold, 1 well above, a smooth ramp across the boundary, and the result is summed into a gain node's parameter. The VCA's own gain sits at zero, so the follower is the only thing that ever opens it.

The knee is what makes this usable rather than a switch, and it is deliberately not a separate control. A hard comparator chatters whenever the signal hovers at the threshold, so the curve ramps across a small band either side of it and the follower's own smoothing does the rest. Everything is audio-rate, which is the part a polling meter cannot do: the gate reacts within a sample of the transient rather than at the next animation frame.