Korora Audio Spira Review

A unique modulation effect derived from a fascinating audio illusion.



Unique and musically engaging tones. Quality construction. Fun and inspiring.

No battery option.


Korora Audio Spira


Ease of Use:



Fifty-five years ago, Roger Shepard devised a fascinating audio illusion. Shepard—who was not a musician or acoustician, but a renowned cognitive psychologist—created a tone that seemed to rise in pitch. And rise. And rise. It seemed to spiral upward forever: a sonic equivalent to the stripes on an old-fashioned barber pole.

What’s the trick? It starts with a group of ascending synthesized tones separated by octaves. The highest note gradually fades till it drops below the level of the next highest note. This dupes our ears into thinking that the tone never stops climbing.

This “Shepard tone” is widely known among electronic musicians, but not so much among guitarists. Or at least that’s what I thought till I read the Wikipedia entry on the phenomenon, which cites its many uses outside experimental music. It’s been deployed in films, including Dunkirk, where it conveys a sense of ever-escalating tension, and in The Dark Knight, where it provides the sound for the Batpod’s engine. It’s been employed by EDM artists as a rise effect, and by rock bands, including Franz Ferdinand and Godspeed You, Black Emperor. And yeah, that’s a Shepard tone in the final section of “Echoes,” that nightmarish soundscape from Pink Floyd’s Meddle album.

Rise Up!
Korora Audio’s Spira deploys the Shepard phenomenon as a phasing/filtering effect. There’s no pitch shifting involved—your dry signal is unaltered. But the effect path is routed through a complex of band-pass (that is, wah-style) filters with resonant peaks in varying octaves. The filter levels vary, generating a resonant phase-like effect that seems to ascend forever. Trippy!

But as cool at this audio illusion is, it may not be the most exciting thing about the Spira. After all, you’re only likely to perceive the effect strongly when other parts don’t compete with the processed guitar. Strum a sustained chord in isolation, and whoa—Shepard city! But with a more active part, or when heard amidst other instruments, you’ll probably perceive it as simply an unusual phasing effect.

This is a new flavor in phasing/flanging, without the mechanical up/down motion that makes some players hate those effects.

And that’s awesome! This is a profoundly different flavor in phasing/flanging, without the mechanical up/down motion that makes some players hate those effects. You get the texture, thickness, and animation of a good phase shifter, minus the repetitious up/down motion. It’s a fresh, ear-catching sound.

Resonant Evil
That’s the Spira’s core sound. But the pedal’s controls provide many variations on that theme.

A wide-ranging rate knob yields everything from fast flickers to super-slow shifts and a sweep freeze at the slowest rate. The blend knob sets the wet/dry balance. The resonance control regulates the prominence of the filter peaks. Maximum settings stop short of chaotic self-oscillation, but you can definitely get over-the-top whoops. Conversely, you might dial in a dry-heavy blend and low resonance for barely perceptible animation.

These are controls you’d expect to find on any phaser/flanger. But the Spira’s two 3-way toggle switches are more idiosyncratic. One switch sets the steepness/strength of the moving filters, from 6 to 12 to 18 dB per octave. The second toggle specifies the number of filters. One setting replicates the classic one-per-octave effect. Another doubles the density, with two filters per octave, each a tritone apart. The third setting splits the difference. Increasing the number of filters yields thicker, more harmonically complex timbres.

And oh—the Shepard effect works with descending filters as well as rising ones. A dedicated footswitch changes sweep direction. There are also internal controls that determine whether the effect defaults to on or off at power up, and defaults to ramp-up or ramp-down, plus an option for pulsing or non-pulsing LEDs. The Spira has no battery compartment, but a 9-volt adapter is included.

The Verdict
The Spira uses an old trick to create new tones. The ever-rising/ever-falling Shepard phenomenon is fascinating. Meanwhile, the pedal introduces new phase/flange flavors, minus their mechanical seesawing at high-resonance settings. The effects are digitally generated, but never cold-sounding. Spira can produce near-subliminal modulation, shrieking freakouts, and everything in between. The build quality is excellent. The results are inspiring.

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