The Shift-Line Prism-9 is a filter pedal in stompbox form, which Shift-Line calls a "Filter Pad." It runs the guitar through a resonant low-pass filter, five low frequency oscillators (LFOs) that modulate the incoming signal, and a built-in reverb. Shift-Line describes the result as enhancing the guitar signal in a way similar to analog synth processing techniques of the late 70s and early 80s1.
The pedal is discontinued: Shift-Line's product page states plainly that the product is no longer made1.
How it works
At the core of the Prism-9 is a 4-pole resonant low-pass filter (LPF), the same kind of filter architecture found on classic analog synths, followed by a reverb. Five LFOs modulate the incoming signal, so the filter's cutoff moves on its own rather than only under your hand. The bypass is active, which Shift-Line says prevents the click of the footswitch from getting into the reverb space12.
Delicious Audio, covering the pedal's unveiling, reported that it started out as a VA synth prototype and gradually transformed into its current form2. The designer's view of how it responds:
"The Prism-9 is not a reverb in its pure sense: to get a noticeable effect from knob tweaks, you have to play notes"
Classic and Modern modes
The pedal has two switchable global modes, Classic and Modern, which Shift-Line says are comprised of the same elements but arranged differently1.
| Classic mode | Modern mode | |
|---|---|---|
| Filter placement | Before the reverb | After the reverb |
| Filter slope | Fixed at 24 dB/Oct | Auto Fat: 24 dB/Oct; Auto: 12 dB/Oct; Manual: 12 dB/Oct |
| Octave sounds | More | Fewer |
| Max LFO speed in Auto modes | Lower | Higher |
In Modern mode's Manual mode, the RATE/DRIPS knob controls filter resonance, from mild operation up to self-oscillation, with maximum Q at 12 o'clock; from 12 to 5 o'clock it enters fat mode with added octaves2.
Controls
The MODE switch selects among the pedal's three modes: Manual, Auto, or Auto Fat1. The other controls change function depending on which mode you are in.
| Control | What it does |
|---|---|
| MODE switch | Selects Manual, Auto, or Auto Fat1 |
| RANGE | Determines the filter cutoff frequency1 |
| RATE/DRIPS (Auto and Auto Fat) | Controls LFO rate, creating a kind of chorus effect when turned clockwise1 |
| RATE/DRIPS (Classic, Manual) | Controls the depth of the sine LFO: 7 to 12 o'clock is regular mode with depth increasing from 0 to max; 12 to 5 o'clock is fat mode with depth decreasing from max to 01 |
| REVERB | Controls reverb amount and decay1 |
| MIX | Controls wet signal volume; dry signal volume is constant and has no control knobs1 |
Note that there is no dry level control: the dry signal stays at a fixed volume, and only the effect level moves with the MIX knob1.
Power and size
The Prism-9 runs on a regulated 9V supply and draws 70mA nominal, which may reach 100mA1.
Shift-Line says a battery might only last for several hours and should be viewed strictly as an emergency option. Use a corresponding power supply for best results1.
The enclosure measures 111 x 60 x 50 mm (4.37 x 2.36 x 1.97"), small enough to fit in a tight spot on a pedalboard1.
Videos
Chords Of Orion
ShurSoma
Questions
What does the RATE/DRIPS knob do on the Prism-9?
It depends on the mode. In Classic mode's Manual mode it controls the depth of the sine LFO, with regular depth from 7 to 12 o'clock and fat mode from 12 to 5 o'clock. In Auto and Auto Fat modes it sets LFO rate, creating a kind of chorus effect when turned clockwise. In Modern mode's Manual mode it controls filter resonance.
How many LFOs does the Shift-Line Prism-9 have?
Five. Shift-Line describes the pedal as a filter pad with 5 low frequency oscillators (LFOs) that modulate the incoming signal, which is what gives it its moving, synth-like filtered character.
Is there a dry level control on the Prism-9?
No. The MIX knob controls only the wet signal volume. The dry signal volume is constant and has no control knob, so you cannot turn the unprocessed signal up or down independently.
How long will a battery last in the Prism-9?
Shift-Line says a battery might only last for several hours and should be viewed strictly as an emergency option. The pedal draws 70mA nominal and may reach 100mA, so a regulated 9V power supply is recommended for best results.
What size is the Shift-Line Prism-9?
The enclosure measures 111 x 60 x 50 mm, or 4.37 x 2.36 x 1.97 inches, making it a compact pedal that takes up little board space.
Is the Shift-Line Prism-9 still made?
No. Shift-Line's product page marks the Prism-9 as discontinued, so it is no longer in production. It is found on the secondhand market rather than new from the maker.
Sources (2)
- A+ Prism-9, Shift-Line, 2026
- Shift Line A+ Prism-9 Filter Pad, Delicious Audio, 2018-12-13
