Warthur The improvised space rock piece Moonloop is a tentpole of Porcupine Tree's The Sky Moves Sideways, but whilst that album has come out in varying configurations over the years, both the original 1CD and later 2CD releases of it only include a fraction of the full 40 minute workout.

Transmission IV presents the full, unedited improvisation. Originally a fan club release, it trickled out in a few more limited editions over the years. Now, benefitting from the remastering job Steven Wilson did for the Delirium Years boxed set, it is now available in that box - or, for those for whom that's a bit too rich a prospect, as a downloadable release.

The Sky Moves Sideways marked the point when Porcupine Tree coalesced from being a Steven Wilson personal project into being a true band prospect, and the Moonloop improvisation finds Wilson and the band's newly-minted rhythm section of Colid Edwin and Chris Maitland working on feeling out their chemistry and really gelling as a group. No doubt a necessary exercise at this stage of the band's evolution, it's also a great little listen, exploring Floydian space territory using more modern equipment.

As with the Voyage 34 EP, this is very much an ambient space rock voyage, so don't expect tight songwriting or compositional structures. (In fact, expect less: this is, after all, an improv.) But if you want to hear the band putting themselves through their paces, it's pretty solid, and if you are very keen on the Sky Moves Sideways sound then it's a no-brainer.