A huge audio console occupies center stage in the Playwrights Horizons’ unhurried and precisely observed world premiere of Stereophonic. This makes sense not only because all of the action is set within the close confines of a music studio, but also because it is an apt metaphor for what playwright David Adjmi and songwriter Will Butler have in mind. Their musical drama chronicles a year in the life of a rock band and its tech team as they go about recording a new album. Decibel levels rise and fall as tensions mount, then subside, while the chance for harmony among the bandmates is continually thwarted by their insecurities, jealousies and self-indulgences. It’s a volatile mix.