From Seymour Duncan:

If you like the smooth, easy-to-dial-in sound of vintage amp tremolo, you'll love the Shape Shifter™ Tap Tremolo. But if you also crave unrestrained versatility and you want to delve into ultra-modern experimental sounds like flutters, shimmers, warbles and even radical "helicopter chops," the Shape Shifter is also your tremolo.

Sonically pure, 100% analog signal path delivers the familiar lush, hypnotic, pulsing tremolo vibes characteristic of ‘50s tube amps. Digital tap control offers incredible control. Shape and Wave controls provide unparalleled versatility.

There are two modes. In Rate mode the tremolo speed varies continuously from one to 20 cycles per second. An LED pulses in time with the tremolo effect for easy Rate setting. In Ratio mode, the speed is established by tapping the Tap Rate switch, allowing for easy synchronization of the tremolo rate with the song tempo. Also, in Ratio mode, the tapped tempo can be expressed in your choice of four tap-to-note ratios: 1:1, 2:1, 3:1, or 4:1 (1/4 notes, 1/8 notes, triplets, or 1/16 notes).

The Wave control allows the tremolo effect to go from the smooth modulation of a sine wave through the sharper characteristics of a triangle wave to the abrupt on/off effect of square wave drive.

Most classic tremolos increase the volume over a certain period if time, say a quarter of a second, and then decrease the volume over a similar period of time. This gives a smooth, even feeling to the tremolo effect. When set to the middle of its range, the Shape Shifter's Shape control does exactly that. But when the Shape control is rotated away from its center position, the relationship between the time spent increasing the volume and the time spent reducing the volume changes. For example, you can dial in one-tenth of a second of volume increase followed by four-tenths of a second of volume decrease, or vice-versa. This adds a very different feel to the tremolo effect. With quick swell and a slow drop, the effect is percussive like a piano. Conversely, with a slow swell and sudden drop, the result is reminiscent of a tape played backwards.