Prism II: Signal Path
The signal path for each of the two channels looks like this:
The incoming signal goes into the three-channel pitch shifting section (octave down, fifth up, octave up). Each of the
three channels has its own low-pass filter (LPF) and can be mixed in with the dry signal; the dry signal can also be
excluded from the mix in Kill Dry mode. Marked with a dotted blue line in the schematic, the pitch shifting section is
additive: it adds new “colors” to the incoming signal. The output of this section goes into the first filter.
All the four filters are identical, each one consisting of a splitter, three filter channels and a mixer. The processed
signal can be mixed with the dry one via the cross-mixing section (filter output can also be subtracted from the dry
signal at a desired ratio).
Each of the three filter channels has a 12dB/Oct slope and controllable resonance:
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The low-pass filter (LPF) cuts off the high frequencies.
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The band-pass filter (BPF) cuts off the low and high frequencies.
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The high-pass filter (HPF) cuts off the low frequencies.
Each of the filters can be offset from the frequency set by the BASE knob. Additionally, each filter has a ratio by
which it is affected by the DEPTH knob. This allows the filters to move in and out of sync, and also in opposite
directions. Combined with the cross-mix, these filter interactions can result in numerous sonic flavors ranging from
classic “wah” sounds to complex notch filtering and even phasing. Since each of the two channels has its own set of
four filters, the Prism II has a very broad sonic palette.
After the two filter blocks, the signal goes into the modulation section.
The mod section has its own LFO which runs independently from the main rate settings. This way, the signal “has a
mind of its own” and doesn’t just follow the main LFO. Depending on the cross-mix section settings, the modulation
blocks can allow you to achieve simple 2-voice chorus effects, vibrato, mild flanging, or anything in between. There
are two modulation blocks, and each one can have different settings.
Following the pitch shifting section, the two filters and the first mod block, the signal goes into the reverb section.
That’s where the real fun starts! Interface-wise, the whole section is represented by a single knob which controls
reverb decay. Each patch has its own dry/reverb mix, but reverb decay can be controlled over a very wide range of
values. When the knob is fully CCW, the reverb section is effectively disengaged; turning the knob fully CW results in
multiple overtones and slowly decaying reflections. The reverb section can be viewed as an envelope generator in a
virtual synth: it allows the attack, hold and release stages to be controlled simultaneously. The resulting sound
greatly depends on which filter blocks (pre/post-reverb) are engaged. Yes, there are two more filters after the reverb
block!
