trance effect (dj sasha)

I bought Wipeout 3 for PSX a couple months ago, and there is this cool song by dj sasha "expander." I want to know what effect or device he is using to create that trance groove. It's just a looped synth line with these constant changing dynamics; tone, pitch, shit I don't even know. Do any of you?

I never heard that song before, but according to your description of how the effect sounds, it seems like it could be flange, or maybe even like a spring or phaser effect.