IF THERE'S one word to describe these two musical partnerships, it's "jugalbandi" – an Indian expression that literally means "entwined twins". To be truly jugalbandi, a musical partnership must feature two players on an equal footing, even if they come from different traditions.

Take Martin Hayes and Dennis Cahill, for example. One is an Irish folk music fiddler, the other a Chicago-born jazz guitarist. Together, though, they operate on an unspoken communicative level that, rightly, conjures up comparisons with Grappelli and Reinhardt.

Their sets are long (sometimes lasting up to 20 minutes), but never boring. Indeed, while such lengthy build-ups in intensity might be a test of endurance for those who aren't aficionados, the journey from quiet, simple melodies to loud, intrinsic shredding can be compelling.

Fiddler Alasdair Fraser and cellist Natalie Haas, meanwhile, come from the folk and classical fields respectively. Their pieces segued together with an almost unnatural fluency, the tempo never faltered and the rapport between them was, as one audience member within my earshot put it, "sweet as a nut".

Then, to round off this energy-sapping but highly educational evening, Hayes and Cahill returned to the stage, joining up with Fraser and Haas to form as a technically challenging and visually impressive string quartet.

Or, if you will, as a double jugalbandi.