The preview season is upon us as comics left, right and mainstream go through the paces on their new shows for next month's Edinburgh Festival. A step up from a dress rehearsal, the preview helps performers fine-tune their laughometers and iron out the non-comedic creases.At the City Arts Centre last Saturday night, two veritable veterans of the Irish comedy scene, Barry Murphy and Kevin Gildea (who were once joined at the hip in the seminal comedy trio Mr Trellis) gave their new shows a run-out before entering the Caledonian cauldron of the Fringe.Murphy's show is a loose, open-ended affair which has him jumping from topic to topic with scant regard for continuity. Kicking off with some very impressive material about school debates (too detailed to go into here) he then vaulted on to some very accomplished stuff about the Eurovision song contest which allowed him to show off his admirable vocal techniques.Murphy's talent has always lain in the originality of his work and his ability to skate and slide through the most unlikeliest of subject matters with aplomb and self-deprecation. It's brave indeed to sacrifice a thematic core or dramatic highlight in your show for a more linear approach.Kevin Gildea is a different proposition altogether: more of a straight stand-up than Murphy in his approach and execution, he engages with the audience on an earthier and more basic level. Sadly missing were the whiplash one-liners of old that identified him as a real comedy talent; these were replaced by more spun-out stories, with a fair whack of his material based on the experience of being Irish in Britain.He hammered home these musings with an extended routine about the genesis of Irish culture, as in describing the origins of traditional dancing. More punch and less jab would have helped the cause, even though he sailed through proceedings with a smile on his, and the audience's, face.