Pseudo stereo effects or ’Stereoizers’ create a stereo signal from a source signal which is possibly (but not necessarily) a mono signal. Actually, many standard effects which are not specifically created to ’stereoize’ such as reverb and chorus will do stereoizing as a side-effect, too. The fact, that various effects have stereo signals as their output even when their input is mono may make you suspect that dedicated stereoizers may also utilize different signal processing algorithms to achieve their goal. And this suspicion is right. A very simple means to stereoize a signal is to delay it a bit (in the range of a few to a few tens of milliseconds) and mix the delayed signal with positive phase to one channel and with negative phase to the other. Note that these added delayed signals will cancel each other out in th mono sum. Spectrally, this will result in comb-filtering both channels with complementary comb-filters. A refinement of this technique is to modulate the delay over time with an LFO. Another refinement would be to filter the delayed signal in order to limit the effect to a certain range of the spectrum - it is often desirable to leave low frequencies untouched (’dry bass’), this could be achieved by highpass-filtering the delayed signal. The delay could also be replaced by a frequency dependent delay (an allpass filter). Another approach would be to apply different (complementary) equalization to the left and right channel or use complementary filter banks. And, of course, one could also combine all these approaches and probably others as well - so, stereoization seems to offer a lot of room for creativity and experimentation.