Korora Audio releases unique filter modulation pedal

If you’ve watched Christopher Nolan’s Dunkirk, you’d remember Hans Zimmer’s astounding soundtrack. In particular, its leitmotif: a droning, electronic pulse that seems to escalate in pitch to infinity, creating tension that never resolves. That’s known as the “Shepard Tone,” and Korora Audio’s new pedal, the Spira, aims to deliver that effect along with other strange sounds.

The Shepard Tone is a type of overlapping glissando. In layman terms, it’s an auditory illusion of a tone whose pitch seems to infinitely ascend or descend, but actually never changes. To produce this effect, the Spira uses the sweep of up to 24 parallel resonant bandpass filters.

There are three modes you can set the filter sweeps to: octave, tritone and a bonus one. In the octave mode, each filter sweeps one octave below the previous one. This continues until the first filter reaches the end of its sweep, and then it starts again an octave below the previous one. This causes the filter to infinitely sweep forward.

In the tritone mode, the number of filters is doubled and spaced half an octave apart. And the bonus mode is a mix between the other two modes, with filters spaced alternately at an octave and half an octave apart.

The pedal has four knob controls: “Rate,” “Resonance,” “Blend,” “Volume.” With the “Rate” set low, the Spira produces the aforementioned Shepard Tone. On the other hand, with the same control set high, it achieves a tremolo modulation that isn’t unlike a flanger or phaser. The “Resonance” knob either deepens or softens the intensity of the effect, and the “Blend” moderates how pronounced it is in your mix.

Finally, you also have the option to set the Spira’s filter rolloff at six dB, 12 dB or 18 dB. Combined with the other controls, this can greatly alter your sound.

It’s all very trippy, but it makes for cool sci-fi/horror effects—especially if you chain it up after a fuzz or distortion.

Listen to the Spira here:

The Spira lists for $299. More information at kororaaudio.com.