The witching hour seems an appropriately freewheeling time for the joyously disorienting sounds emanating from WLRN-FM's (91.3) The Modern School of Modern Jazz. Every Saturday from midnight until 2:00 a.m. Sunday morning, Steve Malagodi guides his listeners through this oasis of avant-garde tunes, wading waist-high into a world of free jazz otherwise considered too deep for South Florida's ears. Although it's no surprise commercial radio fears to tread these challenging waters, it's a relief this show wasn't lost in LRN's recent purge of high-quality local programming. For more than a decade Malagodi has been spinning a mélange of honking saxophones, whispering cymbals, and shuddering drums, making him Miami's source for everything from classic heavyweights Ornette Coleman and Roscoe Mitchell to today's Young Turks. Beyond that his on-air patter never gets mired in the academic aspects. Instead he presents the music with an eagerness as impassioned as the artists he plays. It's an enthusiasm that's infectious.