There is something invigorating about hearing Lily Tomlin laugh. It’s an explosive sound, spontaneous and honest. She has spent roughly 45 years making others convulse with joy onstage doing one-woman shows, in films like “All of Me” and television shows like “Laugh-In.” It’s reassuring, uplifting to know she feels that joy, too. She is inhabited by a cast of characters like Ernestine, the one-time phone company operator turned health care specialist, precocious 5½-year-old Edith Ann, and Tess/Trudy, a homeless woman with a strange and beautiful philosophy about humanity. At 73, Tomlin still makes frequent appearances in film (“Admission”) and television (“Malibu County,” “Web Therapy”), and tours with her characters. She brings them to the Cape Cod Melody Tent Thursday.