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:
- The low-pass filter (LPF) cuts off the high frequencies.
- The band-pass filter (BPF) cuts off the low and high frequencies.
- 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!
The second filter group and mod section are functionally identical to the first ones, but their impact on the sound is dramatically different. By using both filter groups at once or only one of them, you can achieve substantial variations in sound; even more so if you throw modulation into the mix.
The shelving HPF is the final touch to the signal chain. It prevents the Prism II from destroying your lows by reducing the impact of resonant peaks in the lower frequency range.
Following all the processing, the resulting signal goes into the output mix section, where it is mixed with the dry signal via the MIX knob. In Kill Dry mode, the MIX knob acts as the output volume control.