Guca Festival, Guca, Serbia

Each year in August, a tiny hayrick-ringed town in southern Serbia hosts the wildest, noisiest, rawest and probably most popular music festival you have never heard of. Guca attracts nearly half a million people from the Balkans and beyond to the biggest celebration on the planet of trumpet music. But blow those preconceptions from your horn right away. This is a gypsy-derived style that has four settings: mournful, manic, very manic, and terrifyingly frenzied. It sounds like the music of the id, the expression of that dark space in the soul where sex and war and passion are born and bubble and fester.

The 49th Guca Trumpet Players' Gathering, to give its correct title, is built around the prestigious competitions on the main stages about the town, with 130 bands predominantly from Roma background. None is paid – the annual festival is free, and attracts a large number of European youngsters, predominantly French, dementedly swirling their harem pants and dreadlocks. The majority though, are crew-cut Balkan youths, often in forage caps and with militaristic tattoos, but hugely good-natured. And there are no pink wellies, or Justins and Jemimas, and definitely no Jo Whileys. This is a festival of ragged music, in a rough land not long out of a brutal conflict, and it has the raw energy that left fluffy events such as Glastonbury a long time ago.

Away from the official stages, the real flavour of the place is found in the beer-drenched streets, where 10-piece brass orchestras roam the town searching for those who will pay to become the eye of their musical storm. Closer and closer they press their blaring instruments to their willing victim, who hands over money – hundreds of euros by the small hours – for the privilege of being deafened. Each frenzied cell attracts a leaping, spinning, gyrating crowd. It's impossible to ignore the carnal content of the music. It seems designed for people to graze, and grind, and grope with impunity around complete strangers. I'm sure I'll never again see trumpets played against the parts of the human body in quite the way that I saw here.

Adam Tadic, the large, mournful-eyed festival manager, described the gathering – which began in 1961 as a way of preserving Balkan music in what was an increasingly urbanised Yugoslavia – as "Woodstock for trumpets". If it is Woodstock, then its Jimi Hendrix is Boban Markovic. After winning numerous prizes, Markovic stopped competing in 2001. He and his virtuoso son, Marko, now perform at sell out events around the world. He also contributed the soundtrack to the Emir Kusturica movie Underground.

Cream-clad Boban and red-and-pink Marko mounted a twin-trumpet lead over the tightest horn section in town, a three-man percussion section thrashing out complex rhythms, and there was never a hint of world-music crossover blandness.