The Korora Audio Spira is a filter modulation pedal built around the Shepard tone, a sonic phenomenon investigated by Roger Shepard in 1964. It uses a bank of resonant bandpass filters, spaced one octave apart, that sweep through the audio spectrum at a constant rate per octave, creating what Delicious Audio describes as "the illusion of a never-ending, layered, overlapping glissando." It was the debut stompbox from Seattle-based builder Korora Audio, announced on July 18, 2018 at a list price of $299123. As of July 13, 2026, Guitar Pedal X listed the price at $2494.
What it does to your sound
The Spira is not a filter pedal in the wah sense. Instead of one sweeping band, it runs a bank of resonant bandpass filters that sweep continuously, and the octave spacing between them is what produces the Shepard tone illusion of a sweep that climbs or falls without ever arriving. Delicious Audio's product page describes the effect as a "never-ending, layered, overlapping glissando"1.
The density switch sets how the filters are spaced:
- Octave spacing: the classic Shepard effect1
- Tritone spacing: doubles the density of the sweeps1
- Alternating octave and tritone: a spacy and unique effect1
In octave mode, each successive filter sweeps one octave below the previous one until the first filter reaches the end of its range, which is what keeps the sweep going indefinitely2.
The controls
Four knobs and two toggle switches cover the effect, with a dedicated footswitch for sweep direction15.
| Control | What it does |
|---|---|
| Rate | Sets the rate of the sweep, from glacially slow through the tremolo range1 |
| Resolution | Shapes the filter bank1 |
| Blend | Total control over the balance and intensity of the effect1 |
| Volume | Helps ensure just the right level when you punch in the effect1 |
| Toggle switches | Modify the shape of the resonant EQ curve and the density of the sweeps1 |
| Left footswitch | Changes the direction of the sweep between rising and descending filters15 |
The Rate knob goes further than a simple speed control. Turned fully to the left, the filter sweep freezes, producing an effect similar to a comb filter or formant filter. Further clockwise, the sweep speeds up into a warbling tremolo effect1.
Power
The Spira runs on standard 9V DC power and draws 180 mA, with a power supply included2. Premier Guitar's review confirms there is no battery compartment, but that a 9-volt adapter comes with the pedal5.
At 180 mA, the Spira draws more current than many pedals on a shared supply. Give it its own outlet on a pedalboard power supply rather than a daisy chain2.
What reviewers said
Players who tried the Spira at Summer NAMM noted the clear attack and note separation, and its responsiveness to dynamics, according to Korora Audio's press release2. Premier Guitar's reviewer came away with a positive overall verdict, calling the tones unique and musically engaging, and finding the pedal fun and inspiring:
"The build quality is excellent. The results are inspiring."
Videos
Korora Audio
Korora Audio
Mike Hermans
Questions
Does the Korora Audio Spira take a battery?
No. According to Premier Guitar's review, the Spira has no battery compartment, but a 9-volt adapter is included in the box. Plan to run it from a pedalboard power supply or the supplied adapter rather than expecting battery power.
Is the Spira true bypass?
Yes. Korora Audio's press release for the pedal describes it as having soft touch true bypass, so when the effect is off the signal passes through without the filter bank in the way.
What is a Shepard tone?
A Shepard tone is a sonic phenomenon investigated by Roger Shepard in 1964: a set of tones spaced an octave apart can create the illusion of a pitch that rises or falls forever. The Spira applies the same idea with resonant bandpass filters, producing a layered, overlapping glissando that seems never to end.
Can the Spira stop the sweep?
Yes. With the Rate knob turned fully to the left, the filter sweep freezes, producing an effect similar to a comb filter or formant filter. Further clockwise, the rate moves through the tremolo range for a warbling effect.
How much current does the Spira draw?
The press release for the pedal lists standard 9V DC power at 180 mA, with a power supply included. That draw is high enough that a battery is not an option and a daisy chain with other pedals may not be.
Sources (5)
- Korora Audio Spira (Shepard Filter Modulation Effect), Delicious Audio, 2020-10-30
- Korora Audio Unveils New Spira Filter Modulation Pedal, Premier Guitar, 2018-07-18
- Korora Audio releases unique filter modulation pedal, Guitar.com, 2018-07-20
- Guitar Pedal X, Guitar Pedal X, 2026-07-13
- Korora Audio Spira Review, Premier Guitar, 2019-01-04