Shift Line A+ Prism-9

What a filter pad pedal is

The Prism-9 was presented at launch as "a unique, complex, fully-featured effect that embraces analog synthesis techn"iques¹. Where a conventional filter pedal sweeps a tone control over your signal, a filter pad pedal sustains and shapes the guitar into a bed of sound. The Prism-9's circuit combines a resonant low-pass filter, pitch shifting and a room reverb¹, and the maker positions it as an original design meant to contribute to the world of existing modulation effects such as phaser, chorus and tremolo¹.

Delicious Audio, covering the launch, noted that Shift Line pedals have some kind of cultish reputation in the US¹, and summed up the pedal's intent:

The controls

The Prism-9 keeps its control set small, but each knob changes behavior depending on the mode you are in.

The RATE knob is the one that repays close reading, because it does three different jobs:

• Auto and Auto Fat modes: the RATE knob controls LFO rate, creating what the maker calls a kind of chorus effect when turned clockwise¹.
• Classic Manual mode: the trapezoid LFO is disengaged, and the knob controls the depth of the sine LFO, a mode the maker calls DRIPS. From 7 to 12 o'clock it sets regular mode depth from 0 to max; from 12 to 5 o'clock it runs fat mode, with depth going from max back to 0¹.
• Modern Manual mode: the LFO is disengaged, and the knob controls filter resonance, from mild operation up to self-oscillation, with maximum Q at 12 o'clock. From 12 to 5 o'clock you get fat mode with added octaves²¹.

Classic and Modern modes

The pedal has two switchable global modes, "classic" and "modern," which are comprised of the same elements but in different arrangements². The differences are structural, not just tonal:

Because the filter sits before the reverb in Classic mode, the reverb tail is not filtered; in Modern mode the filter comes after the reverb, so the reverb itself is swept by the filter. That ordering difference is the heart of the two modes' character¹².

For bass players, the designer's view is that "The Modern mode seems to work better with bass guitar (although you might like the Classic one, too)"¹.

Power and bypass

The Prism-9 runs on a 9V regulated supply². Its current draw may reach 100mA, so a battery might only last for several hours and should be viewed strictly as an emergency option²¹. For best results, use a corresponding PSU¹.

The bypass is active rather than true bypass: Shift Line says this prevents the click of the footswitch from getting into the reverb space²¹. In practice that means the pedal's circuitry stays in the signal path when bypassed, trading true-bypass purity for quiet switching and a reverb tail that decays naturally.

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