Hi Lance, That's certainly true about the way a screened 4-color process photo works, (although with dot gain the inks ARE often physically mixing to make new colors and/or mud other than CMYK), but we're talking about sounds that are completely _outside_ the frequency range of the instruments being used. For example, when you strike two notes at the same fret on a guitar's B and high E strings, then bend the B up, there's a low sound well below the notes being played that drops down in harmonic relation to the bend. [I have a Tele on which this 'gnnaaooomph' (sp?) is particularly pronounced. My Steinberger sort of does it too, but not as clearly, it's almost unnoticable on my Strats and _completely_ inaudible on my 335, so I'd suspect it has to do with the specific overtones that define a particular instrument's timbre, and also on the response characteristics of your amp/speaker(s).] The colors in a process photo are all within a limited frequency range determined by the inks and paper; as you point out, we see colors other than CMY and K in the photo, but NOT those outside of that gamut, like ultraviolet or infrared, which would be more akin (not exactly, either, but it's an analogy after all) to the psychoacoustic effect we're trying to describe. Maybe a closer optical analogy would be the technique commonly used in Op Art where completely opposite colors are juxtaposed in patterns; magenta right next to green, saturated red next to cyan, black next to white, for example. Our visual sensory system gets overloaded by the contrast and it causes all kinds of neat effects. The colors pulsate, have halos of hues that aren't even present, give the illusion of movement, etc. all without psychedelic assistance. To drag it a bit back ON-topic, one way in which this is relevant to looping is in the way this phenonenon (interaction/disruption of harmonic content) varies depending on where the combination is actually happening. When I use a smaller looping rig in which my straight, looped and otherwise delayed signals are combined into one signal to come out of one amp/speaker, it's a very different sound than when using a larger rig where several discrete signals are amplified separately and come out of different speakers placed in different parts of the room and the combinations occur in the air acoustically. Undoubtably much of it can be attributed to harmonic distortion (since the smaller setup usually ends up getting pushed a lot harder!), but there is a real difference in timbre going on there. Cool stuff! Tim At 10:56 AM 10/14/00 -0700, you wrote: >not to drag this even further off-topic, but there does seem to be some >corollary to the world of optical illusions as well; if we see small dots >of >cyan, magenta, yellow and black in certain combinations, other colors >appear >to us, even though they do not "physically" exist. it's not exactly the >same >as hearing overtones of a fundamental which is not present, but similar, i >suppose...