Improvisation is the key to the power and passion of Persian classical music. But as in the Indian tradition, Iranian musicians follow a complex set of scales, rhythms, and phrases that dictates the repertoire. Rather than being constrained by these rules, the Masters of Persian Music — Kayhan Kalhor (on kamancheh, or spiked fiddle), Hossein Alizadeh (on tar, or long-necked lute), Mohammad Reza Shajarian (vocals), and his son Homayoun (on tombak, or hand drum) — use this common language as a starting point to draw from. Curiously, the musicians' shared vocabulary stems from the poetic meter of the vocalists, who commanded greater respect than instrumentalists in ancient times. This preference may seem like an unfair cultural bias, but it makes perfect sense when you glimpse the translated verses of classic poems like Baba Taher's millennium-old “Saz Va Avaz,” which world-renowned singer Shajarian renders on his collaborative album with Kalhor, Night Silence Desert: “May I die so these teary eyes you shall not see/ My wailing blazing with flames you shall not see/ So wholly shall I roast from your fiery love/ That mine ashes you shall not see!” Clearly, this culture takes its passion seriously. Add the Persian song form ghazal — a mystical union of the sensual and spiritual — and you've got a deeply evocative sound that will make the auditorium walls sweat.