On the face of it, this year's Guinness Jazz Festival was much the same as its recent predecessors. There were the usual massive crowds, spread among four core venues and the numerous watering holes on the fringe. The jazz, artistically speaking the festival's raison d'etre, was generally good. And there was the usual solid reassurance of the main sponsor's commitment to the future.

But there are also signs of an ongoing evolution in the nature of the event that suggest we could see the gradual emergence of a different kind of festival over the next few years. One is the increased willingness of Guinness to accept associate sponsorship on board - a significant crack in the monolithic edifice of the dominance which has made the Jazz Festival synonymous with the Guinness branding alone.

At the moment, one can only guess what this will mean. But if space continues to be created for more sponsors to keep the ship afloat - especially if they are local - that will add to the pressures that are shaping the festival this year and every other.

Some of these are financial. The concentration of big names into Saturday and Sunday, - instead of over three or even four days, as happened in the past - is one sign of that.

But there are other pressures at work, too. The two-faced nature of the programming is evident in the core venues. Audiences primarily interested in the jazz are well catered for at the Everyman Palace Theatre and the Triskel. The place for the modish - epitomised in Courtney Pine's hip-hop and veteran singer Jimmy Scott, disinterred from the graveyard of obscurity and raised to cult status - is now the Opera House.

And nowhere is the split personality of the festival so clear as at the Metropole Ryan, where much needed refurbishment has replaced the faded tat of the past. There is good jazz to be heard there as well as forgettable stuff, but most of the rooms are too small and, with bars adjacent, fans there for the music have to compete with the drinking classes.

If more venues were used to separate and accommodate the dual audience, there would be more opportunity to programme more imaginatively for both sides. But this would also mean the festival would have to respond more effectively to the local community's needs, deepening its roots there while preserving the international cachet the event has built for itself.

That cachet was resoundingly underlined by, among other things, Sunday night's headline concert at the Everyman. Two of the music's most celebrated young Turks, Stefon Harris and Joshua Redman, brought their bands in for a concert of the highest quality. Harris, on vibes and marimba, is the best thing to happen to both in jazz for decades, while Redman has caught the eye as a major figure among young jazz saxophonists, particularly tenors.

Of the two, Harris and his band - Orrin Evans (piano), Eric Revis (bass) and Rodney Green (drums) - had a greater sense of discovery about their work. An inventive treatment of Summertime based on a simple eight-note motif, the witty process of discovering Blue Monk and his development, from that, of There Is No Greater Love, all show Harris as a voice from whom much is expected. Moreover, his Epilogue, a heartfelt, insinuatingly beautiful valediction to the great vibist, Milt Jackson, who died last year, was one of the moments of the festival.

Redman, hugely impressive on tenor, soprano and alto, also had a marvellous band - Aaron Goldberg (piano), Reuben Rogers (one of the bass players of the festival) and Gregory Hutchinson (drums). They did mostly originals, though there was a comparatively straight ahead response to the Parker blues, Cheryl, and an amazing, if overlong, dissection of Eleanor Rigby. If there was a criticism of their work, it was the sense that their level of interplay is now such that they have an answer to every question they ask of each other.

Nevertheless, Redman's work had a feel of a musical imagination at work, in contrast to Bob Berg earlier at the Everyman. Playing a Horace Silver/Art Blakey hard bop style, Berg's tenor was like an aggressive compendium of virtuoso, updated hard bop cliches switched on at will. Both he and his equally virtuosic and aggressively expressed trumpeter, Randy Brecker, were eclipsed by their rhythm section - Kevin Hays (piano), Doug Weiss (bass) and the truly wonderful Adam Nussbaum (drums).

Sharing the bill with them, singer Kurt Elling reinforced the good impression he made at Vicar Street in Dublin earlier this year. So did his gifted trio, led by his longtime pianist, Laurence Hobgood - enough said.

The previous day's fare at the Everyman was more mixed. Violinist Regina Carter's group - Vana Gierig (piano), Chris Lightcap (bass), Alvester Garnett (drums) and a superb Cuban percussionist, Mayra Casales - initially seemed a well-drilled outfit turning out a highly professional show. But on their final two numbers - a modal piece of rhythmic exoticism called Mandingo, and Mojito, an original by trombonist Steve Turre - they hit a groove that was almost hallucinatory.

Things could have been anti-climactic after that. But former Basie alumnus and tenor and flute legend, Frank Wess, stepping in for pianist Jacky Terrasson's group, hit a mainstream groove of his own with his quartet on the second half of the concert.

Saturday night at the Everyman, featuring veteran harmonica player Toots Thielemans and his group, and pianist Ahmad Jamal's trio with tenor saxophonist George Coleman, was ecstatically received by a capacity audience. For me, it was a disappointment. Thielemans, who played as if he was milking the audience for sympathy (he closed with a solo rendition of Danny Boy), was a fussy leader and, to these ears, the band seemed lacking in relaxation. But Stardust, with just harmonica and piano and Thieleman's own chords, was gorgeous.

Jamal, as respected by aficionados as he is loved by the punters, is a personal blind spot, and Saturday did nothing to change that. His trio is good at what it does; it swings superbly, locks as a unit and makes constant use of contrast to motor its performances. But there's a wearying sameness to the approach regardless of the material, underlined when Coleman was finally brought on: they simply weren't flexible enough to change to suit the needs of an extra horn.

Programme clashes meant much of what was on in the Metropole - and in the Triskel - could not be covered, but there was a chance to savour an excellently grooving set by guitarist Tommy Halferty with the Guilfoyle brothers, Ronan and Conor, as well as pianist Jim Doherty sitting in with Cork altoist Len McCarthy's band. (There was some belated acknowledgement of the contribution Irish musicians have made, and continue to make, to the Festival when a surprise new honour was announced, the Guinness Irish Jazz Award. It went, deservedly, to Ronan Guilfoyle, and might have gone some way to making amends for the shabby treatment of Irish jazz musicians in the programme brochure - except that as of noon yesterday Guinness had not informed Guilfoyle himself of the honour.)

A less packed Friday night did provide an opportunity to hear a nice mainstream Norwegian tenor, Bodil Niska, and her blend of Ben Webster and Stan Getz; she was fronting a group which included the fine veteran Scandinavian pianist, Egil Kapstad.

But the huge crowds at the Metropole on Saturday and Sunday defeated attempts to hear Organ Summit, with Jimmy McGriff and Dr Lonnie Smith at the Hammond. And it was disappointing to miss the fine tenor, Joel Frahm, with Kyle Eastwood's group, as well as, earlier, Louis Stewart with Gene Bertoncini.

Overall, though, this was musically a very satisfying festival, with enough in terms of quality to underline its continued importance in the year's arts calendar. But a substantial re-evaluation of its programming and relationship with the community it serves is essential for its continued good health and development.