Over its 13 years — 12 more than founder Ira "Dr. Ike" Padnos might have expected — the Ponderosa Stomp has expanded and contracted, relocated and returned; bade farewell to spring and ushered in fall; made a Circle Bar hop from the Rock 'n' Bowl to House of Blues, The Howlin' Wolf and back again. Participants have died and traditions been born. A biennial since 2011, the festival celebrating the unsung heroes of rock, soul, R&B, gospel and swamp pop seems to carry even greater import now, as an every-other-calendar-year occurrence. The setup remains familiar: A Hip Drop 45 rpm DJ marathon kickoff party (9:30 p.m. Thursday at d.b.a.) and three days of a record swap meet and music history seminars at the AC Hotel by Marriott (221 Carondelet St.), followed by two nights of salon-style bookings at Rock 'n' Bowl — literally all night, as the final scheduled gigs, rockabilly godfathers J.M. Van Eaton, 77, and Roy Head, 74, each start at 2:45 a.m. Debuting this year are Mable John of Motown, Stax and Raelettes fame; Muscle Shoals soul man Willie Hightower; and New Orleans singer/songwriter Jimmy "Pistol" Jules, who composed for Etta James and played with Otis Redding and Marvin Gaye. Regulars returning include southpaw guitar-slinger Barbara Lynn (pictured) and Motown heartbreaker Brenda Holloway. For a full schedule and video previews, visit www.ponderosastomp.com. Single tickets $60; two-day pass $110.