Review: ISP Theta Pro DSP

isp, waller, buck waller, isp technologies, guitar effects, multieffects, multi-effectors
Image placeholder title

The latest addition to ISP Technologies’ Theta guitar systems is one spicy little multieffects pedal. Enclosed in a stunning Ferrari red chassis that’s as tough as the Hulk in anger mode, the Theta Pro DSP ($1,298 street) is a tremendous evolution from the company’s Theta Preamp pedal in both capability and processing power. You get two preamp stages (Clean and Distort), Pre- and Post-EQ (both parametric), onboard Decimator noise reduction, direct-recording features (via the unit’s Intelligent Speaker), a Wah (controlled via an optional expression pedal), a volume-pedal input, a Boost switch (up to +10dB), tap tempo, and six effects (Phaser, Tremolo, Chorus, Flanger, Delay, Reverb).


I always hit new gear sans manual, and the Theta Pro DSP offers pretty effortless operation for anyone who has previously worked with effects menus. I had trouble saving presets initially, as the STORE switch doesn’t save your work until you click the 2nd switch first. You also can’t call up a specific preset’s parameters for editing until you depress the Recall 1 switch. I had to peek at the manual for those—otherwise, everything is easy to dial in by spinning the unit’s Function, Param, and Value knobs. My only regret is there’s no onboard tuner, which meant I had to bring a separate tuner on gigs. It would have been awesome to just plop down “Big Red” and be 100-percent ready to rock.

The chassis and all switches/knobs are robust enough to survive gig abuse, and the large, bright LCD is extremely readable—even if, like me, you’re usually at the mercy of reading glasses. The front row of footswitches is set up to facilitate Song Mode, where you can recall up to four different presets within a tune. That’s definitely smart and appropriate, but for those who prefer working effects on the fly, it may be a tad awkward to click the top row’s effects switches without looking down.

Image placeholder title


Like most multieffectors, the Theta Pro DSP offers preset tones, but I barely listened to them, preferring to mess everything up to my taste. Both preamps—Clean and Distort—provide a wonderful amount of tonesculpting power. I could craft vibey clean tones with aggressive shimmer or bell-like timbres, or more transparent sounds that spotlighted chosen effects. Distort offers Vintage and Theta choices, with Theta being more “metal belligerent” and Vintage allowing more organic and rock-approved grit, grind, and crunch.

Tested with Vox AC30, Fender Champ, and Mesa/Boogie Stiletto amps, I was able to conjure just about any tone I needed, from searing leads to ballsy rhythms, with some lo-fi horrors and brutally saturated textures thrown in the mix. The sounds were all inspiring and fun to play, and every one of my sonic explorations was rewarded with something surprising or darn good. Everyone has their own ideas about what constitutes a “good-sounding” effect, but I found every onboard effect here was useable and commensurate with some boutique flavors.


This is one of the hippest and righteous- sounding direct-recording devices I’ve ever used. Every preset sounded truly realistic—just as if I dropped a Shure SM57 in front of an amp. The speaker-simulator options are fantastic (4x12 Greenback, 1x12 Creamback, 1x12 Deluxe, 4x10 B-man, 2x12 Twin, Lowpass Filter)—though heavy on the American tones—and I loved the Mic Position feature that emulated offaxis and edge-of-cone placement.


Price-wise, the Theta Pro DSP is near the top end of multieffects pedals, and ISP took a minimalist approach to its features, putting the money into tone development, rather than offering lots of different effects types, MIDI, and other options (see “Maker’s Insights”). I don’t use MIDI, so that wasn’t a bummer, and everything I needed as far as effects and gain staging was readily available—excepting my obsession with reverse delay (hey, I’m a psychedelia nerd). So, are the sounds worth $1,300? Absolutely. Just like the Ferrari racers its red finish evokes, this is one badass machine.

Kudos Great sounds. Gig tough. Big LCD. Easy operation (once you peek at the manual).

Concerns No onboard tuner.


By Buck Waller,
ISP Technologies

The first goal of the Theta Pro DSP was tone. We wanted flexibility with preand post-EQ, and not just Bass Mid, and Treble, but full parametric EQ. The available gain had to be huge, and it had to work with both clean and high-gain sounds. Second, in conferring with pro players at NAMM, they asked for an easy-to-use device that was not based on digital- amp models. Third, we wanted zero aliasing (which can often sound like a nonharmonically-related subharmonic that appears in the background when you bend a high note)—especially at high gain. Our oversampled clipping algorithm ensures this doesn’t occur. Fourth, we wanted the Theta Pro DSP to be the most realistic direct-recording unit available. I know we don’t have some bells and whistles in version 1.0 of the Theta Pro DSP that some competitive units offer—such as full MIDI and a computer interface—but we have, in our opinion, the most important feature: the sound.