Think of her as Mauritania's Björk, a Saharan Sade. Noura Mint Seymali melds Arab and North African music with touches of Western pop. Her griot rock entrances with fluttering strings and psychedelic washes of wah wah. We first heard her at the city's World Music Fest. She returns for the Downtown Sound summer series. Ted Sirota's Heavyweight Dub opens with deep grooves.