Santiago. Production Day.

My ears arrived today, which was a source of much excitement. 'Ears', as they are known in the trade, are the in-ear monitors used by today's modern musician, in order to hear what they're playing on stage. They look like a cross between iPod ear buds, old-school hearing aids and vaguely S&M medical appliances, being made to measure from moulded impressions taken from the wearer's ears.

All of the 360 musicians, backline crew and audio techs have these, connected to radio belt-picks so each person can hear whatever they need to hear. Each band member can have their own mix of the stage sounds, emphasising whatever it is they are doing and eliminating anything they don't particularly need. These clever devices have been around for a couple of decades or more, but have now become a fundamental part of amplified performance. I'd heard that they take a bit of getting used to but I've witnessed many musicians (including David Bowie, whose astonishment was rather charming) trying them out and going from uncertainty to true love within minutes.

I'd meant to get myself a set of these for ages because, when I'm on stage with the band during sound check or rehearsal, I'm the only person who can't hear what's going on. The P.A. is no help as the speakers are extremely directional and miles above your head when you're standing on stage. Consequently, without 'ears' all you hear is drums and Edge's rig going off at vast volume. If Bono talks to me via his mic, I can be standing next to him and not hear a word he's saying which isn't especially helpful. I wander about the stage feeling like Tommy and trying to look like I know what's going on. Recently I've been making do, using a set of regular headphones but there's too much sound-bleed for this to be very effective and besides, the 'aspiring-DJ' look doesn't really work for me.

I had the impressions made in London during the last break. It's the same procedure used for making moulded earplugs, but with more precision. Essentially you have a syringe put in your ear, which squirts out a substance akin to modelling clay and toothpaste, creating a thrillingly violating sensation in your ear canal. This is left to set, then extracted with a satisfying squelch before being sent off to the audiologists.

So, as I said, my 'ears' arrived today and I found a quiet corner to try them out. They're an absolute bugger to get in first time, but I am told that one acquires the technique over time. Trying to remove them is equally exhilarating, as the fit is vacuum-tight for isolation. As you tug to remove one plug, it feels like part of your brain is going to come with it.

Anyhow, having got myself comfortable I fired up iTunes and had a listen. I started gently with some Laurie Anderson and in that moment understood David Bowie's astonishment way back when. Talk about hearing voices from god, it's like the sound is being generated entirely inside your head. I felt like Alice in Wonderland, it was such a fantastic, trippy experience. I worked up to some serious kerrang (a young Scottish garage band that I've been enjoying of late, with the rather wonderful name We Were Promised Jetpacks) and was amazed to find that you can make it feel like the all-encompassing rock experience without it having to be overly loud. It's an extraordinarily weird and wonderful sensation. Kind of like what I've always imagined demon-possession must feel like.

Later in the day, when the backline crew were playing and Joe was cranking the P.A., I sat at front of house isolated in my own little bubble, listening to some Oscar Peterson etudes. This is a whole new world of private audio - I've never looked forward to sound check this much in my life.