CAMBRIDGE - Scott Metcalfe's Blue Heron Renaissance Choir finished its season on Saturday with an Iberian anthology to accompany the Museum of Fine Arts' "El Greco to Velásquez" exhibit, focused on the artistic patronage of King Philip III's éminence grise, the Duke of Lerma. Older historians regarded the duke as an unscrupulous mooch; recent revisionists have proposed him as a canny, pro-monarchist political innovator. Regardless, and as the expansive program demonstrated, the duke spent freely on musical adornment.
Douglas Kirk, an expert on music of the duke's court, lent his talents both in programming and as part of the Boston Shawm & Sackbut Ensemble. As Metcalfe and the choir declaimed the plainchant "Vexilla Regis" in an upstage circle, the downstage Ensemble answered with instrumental elaborations by Francisco Guerrero and Juan Navarro - the mellow pungency of cornetts, dulcians, and trombones contrasting with the singers' clarion unisons. (Metcalfe made inventive use of a variety of spatial arrangements.)