Qawwali, the soulful Sufi devotional music of Pakistan and India, no longer enjoys the mainstream attention it did before its greatest practitioner, Nusrat Fateh Ali Khan, died in 1997. There are still loads of fine qawwali artists working today, but none has been able to match Nusrat’s outsize talent and personality; he almost single-handedly popularized pure qawwali in the West but was also willing to experiment, collaborating with the likes of Massive Attack and Bally Sagoo. Rizwan Mujahid Ali Khan and Muazzam Mujahid Ali Khan, the two brothers who lead Rizwan-Muazzam Qawwali, are Nusrat’s nephews, and though their artistry can’t quite match his, last year’s Day of Colours (Real World) is nonetheless terrific. Supported by a traditional vocal chorus, fervent hand claps, frenetic tabla rhythms, and woozy harmonium melodies, they exalt the divine in Punjabi, Farsi, and Urdu. (The florid lyrics, which discuss earthly pleasures, can be interpreted as expressions of conventional love–an element that distinguishes Sufi music from most Islamic music–but the intent is always religious.) Each performance begins at a leisurely gait, but the intensity increases as the song unfolds, cresting with wild vocal improvisations marked by ferocious rhythms and precise melodic ornamentation; the two frequently vocalize in tandem, masterfully and intuitively shadowing each other’s lines. The group isn’t radically advancing the tradition, but opportunities to hear this stuff in the West are rare; I’ve yet to hear a qawwali performance, including this group’s appearance at the Chicago World Music Festival in 1999, that didn’t leave me simultaneously exhilarated and wiped out. Fri 4/15, 8 PM, Old Town School of Folk Music, 4544 N. Lincoln, 773-728-6000 or 866-468-3401, $25, $21 seniors and kids.