Two digital delays with analog control voltage. These are Music From Outer Space modules based on the PT2399 echo processor IC.
With two delays you can get “thru-zero flanging.” For a typical single delay “flanger” effect, there is just a source signal and a delayed version of the same source. With two playback devices it is possible for the devices to switch back and forth between which is the delayed device. When flanging noise slowly, the “thru-zero” point where the delayed device becomes the leading device gives me the subjective feeling of “going somewhere,” reminiscent of the Doppler effect.