Here are two things I just figured out about the Earthquaker Interstellar Orbiter and Fairfield Circuitry's Randy's Revenge. I don't usually do gear posts here and maybe they're obvious to everyone else but I see some confusion about the former online and the latter took me a bit of effort to work out.

Parking the Orbiter

The Interstellar Orbiter consists of two resonant filters running in parallel. There is one frequency control (top right) that controls both, and they're set to oscillate in opposite directions so when one sweeps up the other sweeps down and vice versa. The direct signal and the signals from the two filters are blended using the Direct and (two) Mix knobs into the final output.

There's also an LFO that modulates the frequency. This is also shared by both filters and the rate control is at the top left. Usually with an LFO there's also a depth control, but this seems to be missing here; it's not, though.

Each filter has two controls. Resonance does what you expect -- it sets the Q of the filter. But what does "intensity" do? This is the missing depth control. That is, although the two filters are locked together in terms of rate of the LFO, the depth of modulation can be set separately.

This is the "trick" I discovered this week: setting the intensity to zero for both filters turns the Interstellar Orbiter into a parked (and manually sweepable) formant filter. Turning the mix to zero on either of the filters turns it into (of course) just a straightforward resonant filter. Plugging an expression pedal into the EXP input of the frequency control gives you a sort of wah pedal.

(I think the reason some people think this is not possible is that the natural way to do it would be to zero out the rate control, but that doesn't work; it goes fairly slow but won't stop. In fact what Earthquaker gave us here was really cool. You can have one filter oscillating while the other is parked, a very nice option that wouldn't have been possible with the more "obvious" approach.)

Yes, this is a very expensive way to get a wah pedal, but it opens up possibilities for CV control and live knob-twiddling that make this pedal far more flexible than just the diphthong-generator I've seen in YouTube demos.

Incidentally, this is indeed mentioned in the Orbiter's manual but I've seen folks online assert it's not possible and my second-hand Orbiter didn't some with one, so I doubt I'm the only person to be confused by this.

Here's a demo of the Orbiter:

And here's Kid Koala, who worked with Earthquaker on the design of this unit:

Randy's Revenge as a "Proper" Ring Modulator

Randy's Revenge is a glorious ring modulator in pedal form from Fairfield Circuitry. A ring modulator is just a mixer -- it takes in two signals and outputs one that is a blend of the two. The difference is that a normal mixer blends the signals by adding them, whereas a ring mod does it by multiplying them instead. Psychoacoustically, this tends to produce interesting "sum and difference tones".

(Randy's Revenge is not a "true ring modulator" in the sense that the "ring" in question means a ring of diodes providing rectification of the signal. This is a purely passive device and a very old effect, long predating guitar pedals. But it does offer "true multiplication" thanks to the analogue AD633 chip. But that's enough of that.)

Since effects with two inputs tend to be confusing for guitarists, ring mod pedals usually have an on-board sound generator to act as one of the inputs. Randy's Revenge has a very impressive one that offers sine and square waves going from < 1Hz up to some kind of very high pitch (I guess about 14kHz but could be wrong). This means you can plug the guitar into the "other" input and get a range of lovely sounds, which is what I've been doing for the last couple of years.

But maybe you want to use it as a "normal" ring mod, mixing two signals together. The cryptic, one-page "Programmer's Reference Manual" that comes with it suggests this is possible but is a bit hazy on the details.

In fact it can be done. Set the internal dip sqitches to be off-off-on-off-off-on (reading top to bottom, i.e. 1 to 6) and plug a mono sound source into the CV jack and it will override the internal oscillator, instantly unleashing your inner Stockhausen. (Here "mono" means the ring is grounded).

A couple of words of warning. First, it tries to use impedance to "talk over" the oscillator rather than turning it off, which meant in my tests I always had some oscillator bleedthrough. Maxing out the frequency control makes it barely noticable though, and with the right input impedance this might be completely fixable.

Second, it requires a much higher input level than the guitar input (which of course is instrument level). I don't know how far to push this yet so advise proceeding with caution. I think it might be expecting modular synth level (0-5v) but for obvious reasons you should never hit an input with more voltage than it expects so I'll continue to experiment. For what it's worth, I have tried the headphone out of my laptop turned up on full and the output is still very quiet. Proceed with caution but be aware that feeding in another instrument-level signal (such as something coming off your pedalboard) is unlikely to work.

The good news is that if you unplug your second input the pedal goes back to normal behaviour. You just can't now stick an expression pedal in there without opening the back and messing with the dipswitches again. But to be honest I've never found an expression pedal setting I found all that useful anyway, so my unit will probably stay in that configuration. (In fact I suspect it might be possible to use the ring to drive the LPF threshold but I don't feel like opening the box again today; I'm not sure I'd use that functionality anyway since I have plenty of other ways to achieve that sound.)

Here's Knobs demo-ing Randy's Revenge: