You cant play that scale on a ordinary guitar.
Read this from a Guitar World interview:
Or just read this copy of the part about the scale:
GW: Leaving metaphysics aside, Sex And Religion is a harmonically adventurous album. You seem to be using modes that one doesn’t usually hear in rock and roll.
Vai: That’s another thing that I can’t help. You’re going to hear modes in there that you never heard on any other record or any other type of music, simply because I made them up out of synthetic scales. Like the end of “Deep Down Into The Pain” – that really weird birth sequence. What’s happening is that a child is coming out of the womb, you know? He’s hearing the voice of divinity and asking questions and all this weird stuff. But what you hear in the background is this wild music based on a scale I devised.
GW: A new scale?
Vai: Yeah, I call it the “Xavian” scale. What I did was take the 12-tone tow and make sampled notes of it on the keyboard. Then what I like to do is experiment with different temperaments. [Ed. Note – The 12-note European tempered scale is only one way of dividing up the frequency range between octaves. Different systems exist in other cultures and in the work of composers like LaMonte Young and Wendy Carlos. Some modern synthesizers offer alternate temperaments.]
I have this book where I keep all these different scales, where I divided the octave up into different steps – like maybe 9 or 10 equal steps. I call these scales “fractals.” At the end of “Deep Down Into The Pain” I used a scale that’s based on dividing the octave into 16 equal steps, instead of the 12 steps of the conventional tempered scale. So each half-step within that is not quite a conventional half-step – it’s 60 microsteps as opposed to 100 microsteps. Instead of calling it a half-step, I call it a “quasar.” Then the “whole step” is 120 microsteps, instead of 200 microsteps. Instead of calling it a whole step, I call that a “nova.” All these different intervals create the Xavian scale, a 10-note scale that I extracted from this 16-note row. You take this scale and play chords with it and it’s like divine dissonance, because all the intervals are twisted.
Every six notes or so, you run across a tempered interval. But for the most part, there are not tempered intervals, so you get a whole structure of harmonics that is just eerie and unique. You know how every chord conjures up a different mood? Even to the most casual listener, a major ninth chord will create a different feeling than a minor ninth, or a major ninth with a sharp 11th. Imagine the twisted world of emotions you can open up from the Xavian scale! We human beings are so shaped by music in our evolution. I think that as more people get into experimenting with these fractals, a whole different emotional state of mind will result – one that is probably on a par with the way our evolution is going anyway. But I don’t think you’ll ever hear Metallica jamming on the Xavian scale.
GW: If they read this, maybe they’ll get into it.
Vai: I’ll lend Kirk my 16-fret guitar. You can’t do this stuff on a conventional fretted instrument. I have a guitar that has 16 frets to the octave. Steve Ripley built it for me years ago. He also built me one with 24 divisions to the octave.
GW: So you’ve been experimenting with this for some time?
Vai: Oh, yeah. He built me those guitars about eight years ago.
GW: Are there any other recordings of your with Xavian scales or the like on them?
Vai: No. But there are a couple of weird things. There’s a song called “Chronic Insomnia” on Flexable Leftovers, where I recorded eight different passes of the same melody. Each time I just tweaked the tape speed a little bit, so I ended up with a melody where each note spans and entire half-step. It’s a very dense, eerie-sounding thing. Incidentally, I’m probably going to be remixing Flexable Leftovers and all my other stuff from that period and putting it all onto one disc.