This weekend’s three-day Minimalism festival at Kings Place comes to an end tonight looking at the cross-over between rock and new music in New York in the Seventies. It seems to me that the collision between popular and high-art music produced some of the most dynamic movements of the 20^th century, not only in New York.

There are many ways of breathing new life into Beethoven. Carlos Kleiber used to do it through imagery. He once famously asked his Viennese double basses to play like monkeys during a rehearsal of Beethoven's Seventh. Riccardo Chailly's tactic for his Barbican Beethoven cycle with the Leipzig Gewandhaus orchestra appears to have been to become, if not monkeyish, then at least a bit of a mischievous teenager. Consequently, his first concert saw him throw out the Classical niceties and fill the hall with impish dash and boyish extremes.

William Glock once claimed that Pierre Boulez could literally vomit at music he believed to be substandard. I wonder what he would have made of my friend, who fled at the interval of the opening concert of the Southbank festival on Friday blaming Boulez's Domaines for setting off a panic attack. Her physical response was certainly a welcome corrective to the nonchalance with which the critical world increasingly greets Boulez's language, many of whom still insist that the days of serialism provoking anger or revulsion are in the distant past. Boulez can still upset.

Earlier this year, conductor Manfred Honeck revealed to me his love of old vinyl: the crackle, the fizz, the lost musical traditions. His performances are marinated in this obsession. The idiosyncrasies of his interpretations hark back to a time when the rules were fewer and the colours brighter. Last night was no different. His Mahler Five steered clear of the sleep-inducing modern fixations with orchestral homogeneity and tastefulness and instead jumped right off the deep end.

Dominated by a focus on contemporary music, this year’s Proms’ Saturday Matinees have also developed something of a heavenward glance as the series has progressed. Last weekend it was the Christian mysticism of Hildegard of Bingen at the fore, with Britten’s Sacred and Profane providing a slippery foothold in the earthly. Yesterday we cast off worldly shackles entirely, gazing beyond the limits of our own humanity in the musical visions of Tippett, Tavener and Sofia Gubaidulina.

Sirs Harrison Birtwistle and Peter Maxwell Davies have now been at each others’ heels for almost 60 years. First, the composers were students together at the Royal Manchester College of Music. Then, once their careers began flourishing they kept rubbing against each other in concert programmes. Inevitable, really: the same organisations commissioned them; they were the Twin Peaks of British Modernism. Even now, for old times’ sake, the pair can’t escape each others’ shadow. Since this Proms Saturday Matinee began with Sir PMD’s unaccompanied motet of 1997, Il rozzo martello, we knew Sir HB couldn’t be far behind. And there he was, roaring and savage in Angel Fighter, a very dramatic cantata of sorts, based on the Genesis story of Jacob wrestling with the Angel, written for the Bachfest Leipzig 2010. This was its British premiere.

Forget almost everything you thought you knew about classical music. Forget the regulations and the rigmarole, the politeness and the prissiness. Forget the preening institutions. Forget the vocal doom-sayers. Classical music is in the throes of an extremely welcome revolution. The entrepreneurial spirit that seized and transformed British art in the 1980s is finally animating and unshackling this most stubborn of art forms. Operas are springing up in warehouses, concerts in bars.

One of the weirdest things about the Proms's "weird concerto" theme is that the concertos so far haven't been all that weird. Piano. Violin. Cello and violin. Cello, piano and violin. Pretty familiar stuff. Finally last night we got something bona fide off the wall: a concerto for string quartet from French rebel Pascal Dusapin. Was it weird enough?