1. A method of establishing a vocal demeanor for an application having a speech interface that presents speech content according to the vocal demeanor, the method comprising: determining, from input of a user, at least one first attribute of the user's interaction with the application; specifying, based on an evaluation of the at least one first attribute of the user's interaction with the application, a particular voice family to be used by the application in presenting speech to the user via a speech interface, wherein the particular voice family identifies a particular person's voice by describing an overall nature and timbre of the particular person's voice in specific terms; selecting the vocal demeanor for the application using the specified particular voice family that identifies the particular person's voice as a criterion for the selecting, wherein the vocal demeanor that is selected is configured to present speech using the particular voice family that identifies the particular person's voice that was specified based on the evaluation of the at least one first attribute of the user's interaction; and incorporating, by the application, the vocal demeanor into the application by presenting at least some speech content via the application in the voice family.