We kept moving forward and didn't try to recreate the past .. the approach to each album was radically different every time. Many bands would have some success and, because they were locked into having a single - something we didn't have to worry about - they had to make sure there was something similar on the next album ... that was never the idea with Led Zeppelin .. the goal was to keep that spark of spontaneity at all times.

When I started doing sessions, the guitar was in vogue. I was playing solos every day.

I bet you can't play slide piano.

I can only listen to what I'm working on, at the time. I can't listen to anything else because I don't want to copy it.

I don't want to get too dippy about all this. If you take the view of the scientist and everything is in a state of vibration, then every note is a vibration, which has a certain frequency, and you know that if you put 40 beats into a frequency it's going to be the same note every time. You take that into infrasound and people can be made to be sick, actually killed. Taking it the other way, not to be too depressing, what about euphoria, etc., and what about consciousness being totally... no, I won't go into that one. Time warps.

My vocation is more in composition really than anything else - building up harmonies using the guitar, orchestrating the guitar like an army, a guitar army.

I always felt if we were going in to do an album, there should already be a lot of structure already made up so we could get on with that and see what else happened.