For me, energy is about dynamics and timing. Though there are probably some exceptions out there, music is basically about establishing a beat and playing to that. If it was a computer which played everything, it could establish a beat and calculate exactly where it would be so everything was perfectly on time. Live musicians has to relate to each other... And that's where it gets both tricky, and fun - and where the essence of what is usually called "feel" begins.
Pretty much every musician out there have a flawed sense of time. That's just a consequence of us being human and not machines. Many bassplayers a just a tiny bit too slow, many guitarplayers too eager and get ahead. But as long as that difference is tiny, your human ears won't hear it as out of time, but it will instead give the music a certain feel. Hopefully, this feel proves to be mesmirizing. Really talented/formally instructed musicians can perhaps control this, for self taught rock musicians it's mostly about throwing things together and arriving at a sound... And that's why you have these legendary units, reasonable talented musicians who together sounded incredible. They just happened to click.
With Iron Maiden, it's a bit unusual in that the bassplayer is the eager one... For me, the feel begins and ends with how everyone reacts to the driving bass. With Clive, the band was steady, with Nicko it's more like someone riding a bike and juggling while looking just a bit unsteady. It's certainly an "on one's toes"-feel. But it rarely goes from that to sounding bad, the bicycling juggler keeps making it. To me, being able to recreate that feeling night after night is the reason this band has been able to build a musical empire over the last 40 years.
In a way i get his point, but at the same time i never really thought about the energy level on Maiden records before. I guess the only ones where i hear a significant lack of energy are TXF and VXI, in those records they clearly lost something on that department.
I disagree wholeheartedly. May I enlighten you with a listen to the interlude in "Judgement of Heaven"? Right after the solos, there's a passage where the guitars play a unison melody over a very clear bass & drum backing. Nevermind the melody for now, listen to how Steve locks in with Nicko. It sounds like they could tear the planet apart with that groove.
Could it have been more powerfully mixed, as in (for example) more compressed to stand out more? Sure. But something would have been lost with that too. As it stands,
The X Factor is a very fine example of the band's dynamics and musicianship. Can't say Kevin Shirley really managed to capture that, for all his talk about recording live (and whatever they sounded like originally, the 1998 CD remasters does not sound very good either).