Robert Glasper and Christian McBride spell quality at Sofia’s A to JazZ Festival

In high summer heat, with the backdrop of the Vitosha mountain, the atmosphere in the city's southern park is easy, friendly and relaxed and the three evenings of music on the outdoor stage are offered to the audience completely free, courtesy of their public funders and an array of commercial sponsors. The result is an open air event but without the usual barriers, fences or heavy security and, despite the presence of the various alcohol brand sponsors, a peaceful, good natured 'picnic in the park' vibe with an audience of families and friends of all ages.

Musically, the programme pointed in many directions, both geographically and in terms of its relation to jazz. On Friday night Sweden's Dirty Loops powered through their headliner set of distorted cover versions with a lot more punk-inflected energy than jazz-inflected meaning. The evening had opened with Bulgaria's National Academy of Music Big Band, playing a standard repertoire with a starred first level of ability (a tribute to the discipline of Bulgarian music education) and a drums plus two percussion rhythm section which kept the ensemble breathtakingly tight throughout. Fast pace and driving rhythm characterised much of the festival. Austria's FunkXpress showed just how much they'd learned from their compatriot mentor Joe Zawinul although without his flights of invention. Bulgaria's RomaNero somehow mixed latin rhythms in between the unmistakeable sounds of Roma wedding band music and ancient folk melodies; their countrymen in Jazzanita took contemporary jazz as their homeground but still managed to give much of their set a strong inflection of those frenetic wedding dances.

Local pop stars Angel Kovachev and Dorothy Takev were both, to be honest, more A to X-Factor than A to JazZ, but the Czech/Italian/Bulgarian piano trio of Uvira, Bruno and Hafizi (above) brought the programme back firmly to the jazz of today as they opened on Sunday with a set that featured more reflective music than was heard for most of the rest of the weekend. From neighbouring Slovakia, trumpeter Lukas Oravec and his quartet also gave the Sunday evening audience a set of well-played but workmanlike straight-ahead contemporary jazz; on the Friday, Spanish sextet Mastretta had ranged cheerfully around a mix of earlier, jollier jazz styles.

In truth it was the two American headliners who put the fire and adventure in this A to Z compendium. On Saturday night Robert Glasper (top) proved his band Experiment is just that. What can we do with so many facets of music now available to us? Hell, let's find out in the true spirit of improvisation! The whole set was that kind of roller-coaster exploration in which every member of this remarkable outfit (including bassist Burniss Travis and Glasper on keyboards and Fender Rhodes) pushed the music out and up, with a camaraderie of delight at each other's invention – such as, just for two instances among so many, Casey Benjamin's wild, free saxophone solos, which simply scorched the night air, and Justin Tyson's drumming, which more than justified the use of 'drumkilla' in his email address.

Christian McBride's quartet (a starry combination of the bassist himself, Nasheed Waits on drums, Markus Strickland on tenor and bass clarinet and trumpeter Josh Evans) closed the festival on Sunday night with a masterly exposition of what's at the heart and soul of jazz – freedom, more adventure, empathy, dynamic range, immense skill and (something that eluded several of the other bands at the festival) giving the music space to breathe. Their penultimate number – the simplest of blues - drew some of the most exquisite soloing and interplay and brought the audience to an emotional peak as they cheered with delight for more.

– Story and photos – Robert Beard