here he uses a space robot sound, he does it with his guitar synthesizer.
how to make the sound: you have the normal distortion sound, and then you put a
half step tuned up guitar sound with the first sound, so you play like 2 guitars
you can do this on: Digitech RP 2000 and more, unless you have a guitar synthesizer, so
the riff just repeat it as many times as needed
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|o--/slide on the neck---------------------------------------o|
|o-----------------------------------------------------------o|
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