A polymer interlayer comprising a layer comprising a poly(vinyl acetal) resin having a residual hydroxyl content and a residual acetate content, and a plasticizer, wherein the residual hydroxyl content, the residual acetate content and the plasticizer are selected such that the polymer interlayer has at least one glass transition temperature less than about 20° C. and a peak tan delta of greater than 1.33, and a glass panel having a configuration of 2.3-mm glass//interlayer//2.3-mm glass and at 20° C. has a transmission loss, TLw, of greater than 42 decibels as measured by weighted average sound transmission loss at 2000 to 8000 Hz, and a transmission loss, TLc, of greater than 38 decibels at the coincident frequency is disclosed.