THIS is exactly what it says on the tin: a film about the hugely influential US indie rock band The Pixies, who revolutionised the alternative music scene in the late 1980s and early 1990s (Kurt Cobain confessed to "ripping off" their "loud quiet loud" sonic dynamic for Nirvana's seminal track Smells Like Teen Spirit). Though the band split up in 1993 - singer Charles Thompson (then called Black Francis and now recording as Frank Black) announced the split during a live British radio interview before informing the rest of the band - their music never went away and, when they decided to get back together in 2004, they found themselves playing sold-out gigs that were rapturously received by critics and fans.

It's this reunion tour that directors Steven Cantor and Matthew Galkin document with their film, in the process providing a fascinating insight into the workings of one of the most credible and celebrated bands in the history of rock. Though there was an undeniable commercial imperative behind the reunion (particularly for drummer Dave Lovering, who became a magician to supplement his dwindling royalty cheques), what comes across most clearly is a band trying to get to grips with what made them so special. Their first rehearsal for the tour is a hair-prickling moment as they realise that despite their differences, everything clicks. They're also genuinely humbled by the reverential response they receive from their first warm-up shows.

As the tour progresses, however, we get an insight into what caused the original split. Kim Deal insists on bringing along her sister Kelly (they were also in the band The Breeders together) to keep her off drugs and alcohol. Lovering, whose father is dying of cancer, starts using sedatives and alcohol to help him cope, which leads to onstage bust-ups. Guitarist Joey Santiago increasingly feels the pull of home life, while Thompson tries to decide if he wants to be sucked back into the maelstrom of being in a creative band (he repeatedly dodges questions about recording new material as The Pixies).

They're brutally honest about the fact that they're not really friends. Unlike Metallica they don't see any need to involve a therapist either, because they've essentially realised that when they're on stage everything falls into place, which seems to be enough.

That makes them tough to warm to as people (although the sight of Kim Deal knitting on the tour bus is quite sweet), but just hearing a few bars of Debaser, Where is My Mind? or Wave of Mutilation - originally recorded in this very city - is enough to remind any music fan why The Pixies will always matter.

• Loudquietloud: A Film About the Pixies, tonight 10pm, 25 August 9pm, Cameo; 27 August 12.20pm, Filmhouse;