Named both for the radioactive particle detector and the sci-fi designs of H. R. Giger, Geiger sits between the generative and controlled to produce clicks, honks, and otherworldly but organic wails. While you have a great deal of control over the patch, the outcome itself can be quite difficult to predict, the confluence of many interactions between modulation sources and sound sources.
The basic composition of the patch is not too complex: there are two voices, composed of two sawtooth oscillators and a resonant bandpass filter. Each voice can be brought into the mix, but the most exciting outcomes happen when listening to the outputs derived from interactions between the two voices, via the ring modulator output and the XOR bit modulator output. Here, the variety of modulations and discrepancys in oscillator and filter frequencies and intensities produce all manner of noisy, digital-organic rumbles, rhythms, and roars. There are two LFOs and two shift registers which control the modulation within the patch, and a great deal of cross-modulation between them, to encourage evolving and shifting tonalities.
Finally, a high-pass and low-pass filter pair allow you to shape the output, while a plate reverb provides space, where no one can hear your screams (if the volume’s turned down, I guess).
It’s a lot of fun to play with! If you’re into this sort of thing! And if not, then it’s probably not a lot of fun to play with!
There are (mostly, except where noted) identical voices on the left and right side:
Osc 1 freq — this sets the frequency of both oscillators, but it always sets the frequency of oscillator 1
Osc 2 offset — this is an offset that can be introduced between the oscillator 1 frequency and oscillator 2’s frequency; because the oscillators exist less for harmonic purposes and more as sort of “event initiators” or exciters, inharmonic ratios can often produce better (weirder) results than harmonic ones
LFO 1 depth — this directs LFO 1 (a triangle LFO) to oscillator 1, exclusively
LFO 2 depth — this directs a square wave LFO to oscillator 2, exclusively
RNG depth — this is actually a shift register. For voice 1, the shift register is 5 notes or values long (its product is unquantized). The shift register for voice 2 derives its values from the first shift register, so their outputs are somewhat related, and it is 7 notes or values long. There is a pixel below each RNG depth control to show the present condition of each shift register (before attenuation/inversion)
Bandpass frequency — sets the frequency of the bandpass filter
In the bottom right corner are two controls for modulating each filter.
RNG to filter 1 — this sets the depth that the right side’s shift register modulates the left side’s filter frequency
RNG to filter 2 — this sets the depth that the left side’s shift register modulates the right side’s filter frequency
Resonance — sets the resonance of the bandpass filter; you will want to watch your levels, as more resonance introduces more gain into the circuit, but the patch comes alive when one or both resonances is set above ~.4000
Down the middle are controls for the modulation sources:
LFO 1 rate — this sets the base rate of the triangle LFO (there is a pixel beside it to show the output of this LFO)
LFO 1 to LFO 2 — sets the amount that LFO 1 modulates the rate of LFO 2
LFO 1 to RNG — sets the amount that LFO 1 modulates the rate of the random number generator which produces the shift registers
LFO 2 rate — this sets the base rate of the square wave LFO (there is a pixel beside it to the show the output of this LFO)
RNG rate — this sets a base clock for the shift registers
RNG change rate — this sets a secondary probability for how likely a shift register is to cycle on a given clock; lower change rates will result in more occasions where a value is held for longer than a single clock cycle while at a value of 1, the shift registers will cycle with each clock beat
RNG to LFO 1 — sets the amount that a separate random value (not derived from the shift registers) modulates the rate of LFO 1
RNG to LFO 2 — sets the amount that a separate random value (same as in the previous control) modulates the rate of LFO 2
In the bottom left corner is a mixer:
Vox 1 level — sets the level for voice 1
Vox 2 level — sets the level for voice 2
On their own, the voices can be interesting, but I mostly use them to fill out space/spectra, complementing the next two outputs.
Ring level — this sets the level for the multiplication of the two voices, and its product, influenced by both voices, tends to be more interesting (and unpredictable) than the two individual voices on their own. All the usual expectations of ring modulation apply here, metallic, klangorous tones, sometimes a bit of distortion, atonalities, etc..
XOR level — much like the ring modulator, this produces outcomes based on exclusive-OR operations of the two voices. It shares some similarities to the ring level, but it tends to be noisier and more distorted (the LPF can do a lot to tame/shape it)
There are also controls for the FM amount between the two voices.
Vox 1 to vox 2 FM and vox 2 to vox 1 FM — set the depths of how much each voice FMs the other; these are taken post-bandpass filter
Finally, in the bottom right corner are the “effects.”
HPF freq — sets the high-pass filter frequency and can be used to shape the low end
LPF freq — sets the low-pass filter frequency and can be used to shape the high end
Reverb decay and mix — do what you would expect