“When I got into and started really playing New Orleans jazz more often, it was me working my way back,” says Don Vappie, on break between classes at Loyola University, where he teaches jazz guitar. “It wasn’t just me going back and saying, ‘Oh this is great music.’ This was me coming from where I grew up playing in funk and Top 40 bands and working my way back and seeing how the stuff that happened before me fit into what...