ZT Amplifiers put their name on the map four years ago with the compact Lunchbox solid-state amp. Now they continue along the road less traveled with the Extortion Expressive Distortion. For a departure from tonal convention the pedal features an analog overdrive that can be used on its own or enhanced with a digital signal processing (DSP) circuit.

Housed in a white metal chassis, the true-bypass Extortion offers impressive variability with just a few controls. The Level, Tone, and Drive controls are active once the hard-click Bypass button is depressed, and the Spectral DSP is merged with the signal by way of its own dedicated switch. Staring up from the center of the box is a figure fashioned on the howling character in “The Scream,” Edvard Munch’s quintessential work of Expressionist art. So … is the pedal expressive?

ZT’s unique approach to distorted voices is based almost entirely on EQ contouring, which starts with the analog circuit’s Tone control. Rather than sweeping bass and treble like a conventional tone knob, this one functions more like a graphic EQ. Mids are cut to the left of 12 o’clock (where the EQ is flat) and boosted to the right, with different high- and low-frequency settings on independent curves around the dial.

Depending in part on how the tone is set, the quality of the Drive control can be flappy like a Fuzz Face, edgy like an ’80s Marshall, hollow like an overdriven AC30, or more subtle like a soft gain – with a half-dozen variations between each. The boutique analog overdrive that ZT mentions is likely in there with a little tweaking.

Without the DSP engaged, the last stop before the signal heads out to the amp is the Level control. But stomping on the Spectral DSP bypass changes everything, adding a sweepable filter both before and after the analog circuit to create a genuine hybrid overdrive – or, as ZT calls it, “an analog/digital mutant.” The unusual function of this DSP algorithm filters just the distortion without affecting the EQ of the guitar signal. Rotating the Spectral DSP knob counterclockwise essentially broadens the low end of the distortion while a clockwise turn sharpens its high end, so it’s something like the filter in a wah pedal except that it sweeps only the distortion.

By selecting a contour with the Spectral DSP knob, a player can hone in on a specific distortion frequency to lend more thud to a thumping rhythm or more edge to a searing lead. For direct access to the entire range of the Spectral DSP, an expression pedal can be plugged into the pedal’s Control input, allowing for some pretty sick tones (in a good way), from a distorted horn to something akin to ring modulation to more nuanced effects like softened upper frequencies that shave the cutting edge off of high notes. Other stompboxes may provide the flexibility to dial in a variety of distortions, but none enable a player to vary them on the fly quite like this.

While the Spectral DSP gets all the cachet, the pedal’s secret weapon is really the Tone knob. The way the available tone contours interact with the Drive control deserves some time and attention. Once a sound is established between these two parameters, the Spectral DSP provides a good time by again multiplying the variables. After testing the Extortion with a handful of rigs, the strongest tones – with a hard leading edge for attacks and a fat back end – were best suited to metal and thrash, though there’s something here for anyone willing to stray off the beaten path.

There is a squash factor to consider with the Extortion. In more settings than not, it can squeeze and narrow tone like many other distortions do, but some tweaking of the Tone and Spectral DSP controls recovers desired fundamental qualities while distorting different guitars (particularly if the Drive isn’t set too high): a PRS is still creamy, a lightly overdriven Tele still has snap, and a Les Paul on the neck pickup is still nicely rounded. The pedal also provides a host of interesting things to do with a deliberately squashed tone. In the right hands, ZT’s Extortion can expand the available palette of distorted tones and radicalize a player’s sound.

This article originally appeared in VG October 2013 issue. All copyrights are by the author and Vintage Guitar magazine. Unauthorized replication or use is strictly prohibited.