It's pretty much all in the pedal, but it takes some time to get the feel of it (which means some of the control is in the guitar too, I suppose). As you change pitch, the circuit reacts in a semi-sluggish way, trying to track the frequency (it is PLL-based). There is a lot of overshoot and ripple in the oscillator frequency as it tracks, which gives it that sort of slurring vibrato effect. As the note rings out, eventually the oscillator frequency will return to zero and go silent (like a gating effect).