The BSRI Audio Geometry Stacks is an analog flanger built around a bucket brigade device (BBD) delay, the short-delay circuit that analog flangers use to create their sweeping, comb-filtered sound. BSRI Audio says the pedal "opens up many little modulation universes that can be delicate and subtle or mechanical and extreme"1. Its distinguishing feature is a second footswitch, Extend, which cascades an additional BBD into the modulation path for more dramatic flanging effects1. It sits among the many analog flangers on the site, from the MXR Flanger to the Electro-Harmonix Deluxe Electric Mistress, with its own take on the format. For more on the effect itself, see Flanger Pedals.
The controls
The Geometry Stacks carries five knobs and one toggle, each aimed at a different part of the flanging effect:
| Control | What it does |
|---|---|
| Level | Sets the volume of the modulated signal mixed into the output1 |
| Voice | Active shelving treble boost/cut1 |
| Enhance | Sets the amount of signal returned to the start of the BBD for regeneration1 |
| Width | Sets the range the modulation sweeps, from narrow to wide1 |
| Velocity | Sets the frequency of the modulation, from very slow to very fast1 |
| Polarity (toggle) | Sets the polarity of the modulated signal at the mix stage1 |
Enhance is the regeneration control, and it is the one to treat with care. BSRI Audio warns that "This control can cause self-oscillation at maximum so be careful!"1. Delicious Audio's Paolo De Gregorio, writing when the pedal appeared in May 2026, described it the same way: "Enhance: Regeneration. Feedback. How much signal gets sent back through the bucket brigade. Low settings are rich. High" settings self-oscillate and get loud at the extremes2.
Width and Delay interact in a way worth knowing. Width sets how far the modulation sweeps, and at maximum it sweeps the full range of the Delay control, which then has no effect of its own1. If the Width control is at minimum, the Delay control instead allows for manual sweep of the flanger effect, letting you sweep the flange point by hand1.
The Polarity toggle changes the character of the flanging itself. Down is in phase with the dry signal for classic flanging sounds. Up is out of phase with the dry signal, which BSRI Audio describes as "a unique hollow or tubular sounding effect"1.
Footswitches: Activate and Extend
The Geometry Stacks has two footswitches, which is unusual for a flanger:
- Activate is the true bypass soft-click footswitch that turns the effect on and off1. De Gregorio put it plainly: "Activate: True bypass footswitch. On. Off. Clean."2
- Extend cascades an additional bucket brigade device into the modulation path for more dramatic flanging effects1. In practice, it stacks a second BBD stage into the circuit while you play, so the flanging can be taken deeper than a single-BBD design allows, and then returned to the standard sound with a tap.
At maximum Enhance the pedal can self-oscillate, and high Enhance settings get loud at the extremes, so back the control off before raising it on a live stage12.
Videos
ambienttrash
collector//emitter
Fullpedal Alchemist
Sources (2)
- Geometry Stacks, BSRI Audio
- New Pedals: BSRI Geometry Stacks Flanger, Delicious Audio, 2026-05-18
