A interesting audio illusion can be made by playing 8 or 10 octave notes together, then going up to the next half step and playing them again, and so on increasing pitch by a half step each tile. PLUS: The amplitudes of each note are reduced at the upper and lower ends. (A Gaussian shaped amplitude envelope works well, possibly even a linear function.) To add clarity: follow one note, say a low bass note, as it increases in pitch. It begins at the lowest volume and increases in volume until it reaches about middle C in pitch, then it starts decreasing in volume. It sounds like an increasing pitch but it always remains at mid scale - like an Escher stairway that keeps going around on itself.

I would like to make this illusion but don't have the tools. If any eager beaver wants to try this and send me an AIFF copy, it would be appreciated, but I would me satisfied if someone could point me to a free software package or two where I could do my own.

Thanks bikerbillyboy

I tried this once with my Nord modular. It was impossible to get the pitches to line up accurately, but what I got sounded pretty cool. I also did something like this on a Commodore 64 for a psychology school project, but only had 3 oscillators so it wasn't convincing. You might want to try C sound or something like that.

By the way, the name of the effect is "Shepard tones", named after Roger Shepard. So you might be able to search for information on it. Good luck,
John

John, thanks much for the reference to Shepard Tones. Lots of finds from Google. Haven't looked at them all yet. Interesting, though, that Shepard gets the credit. Sometime not long after 1966 when I moved to NASA (in MD), Hamming of Bell Labs gave us a lecture about the power of the computer for use in the future. He said we would probably do experiments in the computer rather than in the laboratory. (I saw Cray computers being used extensively to simulate atomic explosions - maybe still are.) Hamming's book on numerical methods was a classic at that time. To get to the point, Hamming played that illusion. The impression stays with me. Shepard gets the credit.

Bill

Brian May did something similar with a Guitar line on the beginning and end of Queen's 'A Day At The Races', way back when.