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    The modulation you hear in "Long Tube Trio" is not electronic. The Long Tube is a 9.5 foot x 1.5 inch aluminium tube which I perform with by singing into it. I first started laying the tube while working at The Exploratorium in 1990. I had discovered a phenomenon whcih occurs in a tube which is open at one end where certain pitches are cancelled out, unable to sound. I found out that singing into the tube physically modulated my vocal cords, producing a number of interesting sounds. The physicist's explanation for this is that sound waves travel down the tube to its open end and return 180 degrees out of phase, trying to cancel out the closed end of the tube (i.e. my vocal cords -- it's a weird senesation, as if someone were touching your throat.)

    The other explanation offered has to do with impedence mismatchi, both between the different diameters of the tube and my throat, as well as the difference in air pressure between the inside of the tube and the outside world.

    The pitches that are unable to sounds are the ones that I concentrate on while singing. In the 9.5 foot long tube, those putches are the harmonics above roughly an "A" 55hz fundamental.