equipment question

And the open-ended modulations they're doing are a lot like the ones on analog synths (and their software replicas), with their subtractive synthesis, multiple oscillators, resonant filters, noise generators, and so on. It's very easy to make amelodic noises and drones with them, and then modulate and control them in a million different ways.

So I dunno if I can answer your question specifically, but I'm pretty sure the thing you're looking for lies in that direction -- things like ring modulators and resonant filters in particular have a lot to do with the sounds you're talking about.

http://www.jazzmagazine.com/Musique/oreille/images34/merzbowint2.jpg

J.

For instance, a ring modulator just takes a signal and multiplies the frequency (I think multiplies) by that of another signal. One thing changes the other. So you might plug an instrument into one, and the unit might modulates the instrument signal based on something else -- perhaps a frequency that it's creating internally, like a sine wave. (And it might have knobs to let you control what kind of sine wave.) So it creates a much more complicated sound, and one that can sound disharmonic or noisy or bad if you want it to.

You can get something like that as a stand-alone box. They're also built in to lots of other devices, like complicated analog-style synthesizers. You know those old analog synths, like Moogs, with all the input jacks and patch cords hanging everywhere? Those work entirely on the "one thing modulates another" principle. The basic sounds they "create" are just sine waves (or square waves, or sawtooth waves, or random noise) -- most everything else you get out of them is by specifying that this sine wave will be affected by that square wave, this wave here will affect the pitch or volume (or whatever) of that wave there ... on and on until you have a sound that's really complex, and, if you want it, really noisy and jacked-up and weird. The basic "one thing modulates another" pieces, the circuits and units, can be used for any sound you want.

Hopefully that makes more sense. The other thing I mentioned was resonant filters: those just process sounds by cutting out different parts of the frequency spectrum, almost like an extreme form of EQ. But you can control and change what they're cutting, which creates interesting effects, and you can control their "resonance," which is how much they're emphasizing the frequencies right around the part you cut. That sounds overly technical, but the point is that the "resonance" part creates a sound that's used often by the artists you're talking about.